Occurrence of Salt, pH, and Temperature-tolerant, Phosphate-solubilizing Bacteria in Alkaline Soils

An ecological survey was conducted to characterize 4800 bacterial strains isolated from the root-free soil, rhizosphere, and rhizoplane of Prosopis juliflora growing in alkaline soils. Of the 4800 bacteria, 857 strains were able to solubilize phosphate on plates. The incidence of phosphate-solubilizing bacteria (PSB) in the rhizoplane was highest, followed by rhizosphere and root-free soil. Eighteen bacterial strains out of 857 PSB were able to produce halo at 30°C in a plate assay in the presence of 5% salt (NaCl) and solubilize tricalcium phosphate in National Botanical Research Institute's phosphate growth medium (NBRIP) broth, in the presence of various salts, pHs, and temperatures. Among the various bacteria tested, NBRI4 and NBRI7 did not produced halo in a plate assay at 30°C in the absence of salt. Contrary to indirect measurement of phosphate solubilization by plate assay, the direct measurement of phosphate solubilization in NBRIP broth assay always resulted in reliable results. The phosphate solubilization ability of NBRI4 was higher than in the control in the presence of salts (NaCl, CaCl₂, and KCl) at 30°C. Phosphate solubilization further increased in the presence of salts at 37°C as compared with 30°C. At 37°C, CaCl₂ reduced phosphate solubilization ability of NBRI4 compared with the control. The results indicated the role of calcium salt in the phosphate solubilization ability of NBRI4. Received: 9 March 1999 / Accepted: 16 April 1999     

Comparing temperature sensitivity of bacterial growth in Antarctic marine water and soil

The western Antarctic Peninsula is an extreme low temperature environment that is warming rapidly due to global change. Little is known, however, on the temperature sensitivity of growth of microbial communities in Antarctic soils and in the surrounding oceanic waters. This is the first study that directly compares temperature adaptation of adjacent marine and terrestrial bacteria in a polar environment. The bacterial communities in the ocean were adapted to lower temperatures than those from nearby soil, with cardinal temperatures for growth in the ocean being the lowest so far reported for microbial communities. This was reflected in lower minimum (T_min) and optimum temperatures (T_opt) for growth in water (?17 and +20°C, respectively) than in soil (?11 and +27°C), with lower sensitivity to changes in temperature (Q₁₀; 0–10°C interval) in Antarctic water (2.7) than in soil (3.9). This is likely due to the more stable low temperature conditions of Antarctic waters than soils, and the fact that maximum in situ temperatures in water are lower than in soils, at least in summer. Importantly, the thermally stable environment of Antarctic marine water makes it feasible to create a single temperature response curve for bacterial communities. This would thus allow for calculations of temperature‐corrected growth rates, and thereby quantifying the influence of factors other than temperature on observed growth rates, as well as predicting the effects of future temperature increases on Antarctic marine bacteria.     

CYANOBACTERIAL DOMINANCE OF POLAR FRESHWATER ECOSYSTEMS: ARE HIGH-LATITUDE MAT-FORMERS ADAPTED TO LOW TEMPERATURE?1

Although it is generally believed that cyanobacteria have high temperature optima for growth (> 20° C), mat-foming cyanobacteria are dominant in many types of lakes, streams, and ponds in the Arctic and Antarctic. We studied the effect of temperature on growth (μ) and relative pigment composition of 27 isolates of cyanobacteria (mat-forming Oscillatoriaceae) from the Arctic, subarctic, and Antarctic to investigate whether they are a) adapted to the low temperature (i.e. psychrophilic) or b) tolerant of the low temperature of the polar regions (i.e. psychrotrophic). We also derived a parabolic function that describes both the rise and the decline of cyanobacterial growth rates with increasing temperature. The cyanobacteria were cultured at seven different temperatures (5°-35° C at 5° C intervals), with continuous illumination of 225 μmol photons.m⁻².s⁻¹. The parabolic function fits the μ-temperature data with 90% confidence for 75% of the isolates. Among the 27 isolates of cyanobacteria studied, the temperature optima (T_opt) for growth ranged from 15° to 35° C, with an average of 19.9° C. These results imply that most polar cyanobacteria are psychrotrophs, not psychrophiles. The cyanobacteria grew over a wide temperature range (typically 20° C) but growth rates were low men at T_opt (average μ_max of 0.23 ± 0.069 d⁻¹). Extremely slow growth rates at low temperature and the high temperature for optimal growth imply that the cyanobacteria are not adapted genetically to cold temperatures, which characterize their ambient environment. Other competitive advantages such as tolerance to desiccation, freeze—thaw cycles, and bright, continuous solar radiation may contribute to their dominance in polar aquatic ecosystems.     

Phosphate solubilization potential and modeling of stress tolerance of rhizobacteria from rice paddy soil in northern Iran

The purposes of this study were to evaluate the phosphate solubilization activity of bacteria isolated from the rhizosphere of rice paddy soil in northern Iran, and to study the effect of temperature, NaCl and pH on the growth of these isolates by modeling. Three of the most effective strains from a total of 300 isolates were identified and a phylogenetic analysis was carried out by 16S rDNA sequencing. The isolates were identified as Pantoea ananatis (M36), Rahnella aquatilis (M100) and Enterobacter sp. (M183). These isolates showed multiple plant growth-promoting attributes such as phosphate solubilization activity and indole-3-acetic acid (IAA) production. The M36, M100 and M183 isolates were able to solubilize 172, 263 and 254 µg ml^?1 of Ca₃(PO₄)₂ after 5 days of growth at 28 °C and pH 7.5, and to produce 8.0, 2.0 and 3.0 μg ml^?1 of IAA when supplemented with l-tryptophan (1 mg ml^?1) for 72 h, at 28 °C and pH 7.0, respectively. The solubilization of insoluble phosphate was associated with a drop in the pH of the culture medium and there was an inverse relationship between pH and solubilized P (r = ?0.98, P < 0.0952). There were no significant differences among isolates in terms of acidity tolerance based on their confidence limits as assessed by segmented model analysis and all isolates were able to grow at pH 4.3–11 (with optimum at 7.0–7.5). Based on a sigmoidal trend of a three-parameter logistic model, the salt concentration required for 50 % inhibition was 8.15, 6.30 and 8.23 % NaCl for M36, M100 and M183 isolates, respectively. Moreover, the minimum and maximum growth temperatures estimated by the segmented model were 5.0 and 42.75 °C for M36, 12.76 and 40.32 °C for M100, and 10.63 and 43.66 °C for M183. The three selected isolates could be deployed as inoculants to promote plant growth in an agricultural environment.     

Thermophilic bacteria that tolerate a wide temperature and pH range colonize the Soldhar (95 °C) and Ringigad (80 °C) hot springs of Uttarakhand,India

Twenty-eight bacterial cultures, isolated from hot springs in Uttarakhand, were characterized with particular reference to their wide temperature and pH tolerance and production of enzymes in the thermophilic range. All the bacterial isolates were observed as Gram-positive or variable rods in varied arrangement. Bacterial isolates exhibited tolerance to a wide temperature range (20–80 °C), from mesophilic (+11° to +45 °C) to thermophilic (+46 ° to +75 °C); few almost reached the hyperthermophilic range (+76 °C). The isolates also tolerated a wide pH range (4–14) and moderate salt concentration. The optimum growth of the bacterial isolates was observed at 55 °C and 7 pH. Out of 28 isolates, 25 produced lipase, 25 amylase, 24 cellulase, 22 protease and 13 xylanase at 55 and 65 °C. Tolerance to a wide temperature and pH range and the production of enzymes in a thermophilic temperature range can be considered as indicators of ecological competence of these bacterial isolates for colonizing the high temperature environment. On the basis of 16S rDNA similarity, 20 bacterial isolates belonged to Bacillus licheniformis, five to Paenibacillus ehimensis and one each to Bacillus sonorensis, B. tequilensis, and Staphylococcus epidermidis. Besides variation in phenotypic characters, strains of B. licheniformis and P. ehimensis showed varying 16S rDNA similarity between 97–99 % and 95–99 %, respectively. Consideration of temperature preferences in classifying microorganisms on the basis of their minimum, maximum, and optimum growth requirements is also discussed. The study has ecological relevance in the context of colonization of high temperature environments by thermophilic bacteria.     

Temperature controls on aquatic bacterial production and community dynamics in arctic lakes and streams

The impact of temperature on bacterial activity and community composition was investigated in arctic lakes and streams in northern Alaska. Aquatic bacterial communities incubated at different temperatures had different rates of production, as measured by ¹⁴C‐leucine uptake, indicating that populations within the communities had different temperature optima. Samples from Toolik Lake inlet and outlet were collected at water temperatures of 14.2°C and 15.9°C, respectively, and subsamples incubated at temperatures ranging from 6°C to 20°C. After 5 days, productivity rates varied from 0.5 to ～13.7 µg C l^?1 day^?1 and two distinct activity optima appeared at 12°C and 20°C. At these optima, activity was 2‐ to 11‐fold higher than at other incubation temperatures. The presence of two temperature optima indicates psychrophilic and psychrotolerant bacteria dominate under different conditions. Community fingerprinting via denaturant gradient gel electrophoresis (DGGE) of 16S rRNA genes showed strong shifts in the composition of communities driven more by temperature than by differences in dissolved organic matter source; e.g. four and seven unique operational taxonomic units (OTUs) were found only at 2°C and 25°C, respectively, and not found at other incubation temperatures after 5 days. The impact of temperature on bacteria is complex, influencing both bacterial productivity and community composition. Path analysis of measurements of 24 streams and lakes sampled across a catchment 12 times in 4 years indicates variable timing and strength of correlation between temperature and bacterial production, possibly due to bacterial community differences between sites. As indicated by both field and laboratory experiments, shifts in dominant community members can occur on ecologically relevant time scales (days), and have important implications for understanding the relationship of bacterial diversity and function.     

Novel P-Solubilizers from Calcium Bound Phosphate Rich Pine Forest of Lower Himalaya

Phosphorus, an essential element for life, is continuously depleting from soils and thus demands sustainable management particularly in agriculture and forestry. Inorganic P constitutes the major proportion as tricalcium phosphate in soils of lower Himalayan region of Pakistan. We sampled these soils and screened for P-solubilizing microbes. A range of culturable microbial community (bacteria and fungi) was isolated and molecularly characterized which make the P available from mineral phosphates. There was an increase in abundance of phosphate solubilizing bacteria (PSB) at a 6-inch depth of the pine rhizosphere compared to the surface soil samples. Moreover, the isolates from lower Himalaya have higher abundance and better efficiency to solubilize the inorganic P than the ones from non-Himalaya. Most likely the P-solubilization done by our P-solubilizing microbes is via acidification as we observed the decrease in pH of the medium of microbial growth. Furthermore, the majority of isolated PSB belong to gammaproteobacterial class of Gram negative bacteria. Most interestingly, 13% of our isolated PSB were psychrotolerant (physiologically active at cold environment, i.e., 4°C) and able to solubilize inorganic P as efficiently as at ambient temperature. This study is unique in reporting the P-solubilizing microbes, particularly the psychrotolerant bacterial strains, of Lower Himalaya. Therefore the isolated bacterial and fungal strains have potential and may serve as biofertilizers in the region to increase the P availability in soils.     

Temperature adaptation of soil bacterial communities along an Antarctic climate gradient: predicting responses to climate warming

Soil microorganisms, the central drivers of terrestrial Antarctic ecosystems, are being confronted with increasing temperatures as parts of the continent experience considerable warming. Here we determined short‐term temperature dependencies of Antarctic soil bacterial community growth rates, using the leucine incorporation technique, in order to predict future changes in temperature sensitivity of resident soil bacterial communities. Soil samples were collected along a climate gradient consisting of locations on the Antarctic Peninsula (Anchorage Island, 67 °34′S, 68 °08′W), Signy Island (60 °43′S, 45 °38′W) and the Falkland Islands (51 °76′S 59 °03′W). At each location, experimental plots were subjected to warming by open top chambers (OTCs) and paired with control plots on vegetated and fell‐field habitats. The bacterial communities were adapted to the mean annual temperature of their environment, as shown by a significant correlation between the mean annual soil temperature and the minimum temperature for bacterial growth (T_min). Every 1 °C rise in soil temperature was estimated to increase T_min by 0.24–0.38 °C. The optimum temperature for bacterial growth varied less and did not have as clear a relationship with soil temperature. Temperature sensitivity, indicated by Q₁₀ values, increased with mean annual soil temperature, suggesting that bacterial communities from colder regions were less temperature sensitive than those from the warmer regions. The OTC warming (generally <1 °C temperature increases) over 3 years had no effects on temperature relationship of the soil bacterial community. We estimate that the predicted temperature increase of 2.6 °C for the Antarctic Peninsula would increase T_min by 0.6–1 °C and Q₁₀ (0–10 °C) by 0.5 units.     

Photosynthetic capacity and leaf nitrogen decline along a controlled climate gradient in provenances of two widely distributed Eucalyptus species

Climate is an important factor limiting tree distributions and adaptation to different thermal environments may influence how tree populations respond to climate warming. Given the current rate of warming, it has been hypothesized that tree populations in warmer, more thermally stable climates may have limited capacity to respond physiologically to warming compared to populations from cooler, more seasonal climates. We determined in a controlled environment how several provenances of widely distributed Eucalyptus tereticornis and E. grandis adjusted their photosynthetic capacity to +3.5°C warming along their native distribution range (~16–38°S) and whether climate of seed origin of the provenances influenced their response to different growth temperatures. We also tested how temperature optima (T_opt) of photosynthesis and J_max responded to higher growth temperatures. Our results showed increased photosynthesis rates at a standardized temperature with warming in temperate provenances, while rates in tropical provenances were reduced by about 40% compared to their temperate counterparts. Temperature optima of photosynthesis increased as provenances were exposed to warmer growth temperatures. Both species had ~30% reduced photosynthetic capacity in tropical and subtropical provenances related to reduced leaf nitrogen and leaf Rubisco content compared to temperate provenances. Tropical provenances operated closer to their thermal optimum and came within 3% of the T_opt of J_max during the daily temperature maxima. Hence, further warming may negatively affect C uptake and tree growth in warmer climates, whereas eucalypts in cooler climates may benefit from moderate warming.     

The effect of temperature on the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) tail meat during storage

Aims: The aim of this study was to update and extend our knowledge of the bacterial load and microbial composition in Norway lobster (Nephrops norvegicus) under commercially relevant storage conditions to optimize handling procedures. Methods and Results: Total viable counts were performed at different storage temperatures (0, 4, 8, 10, 12 or 16°C) and after different storage times (1–7 days). Storage at 16°C was found to be most detrimental, and storage at 0°C was found to be optimal. 16S‐rRNA sequencing was utilized to determine the composition of the bacteria within the microflora. In this way, Photobacterium isolates, especially Photobacterium phosphoreum, were identified as the main specific spoilage organisms. The abilities to reduce trimethylamineoxide (TMAO) and to produce H₂S were analysed in a selection of bacterial isolates. The higher the incubation temperature during storage, the more isolates were found to reduce TMAO and produce H₂S. Conclusions: Nephrops norvegicus possesses an unusually high initial microbial load when fresh. Storage temperature is the most crucial factor affecting microbial growth, microbial activity and spoilage potential in N. norvegicus produce. Spoilage can be attributed mainly to P. phosphoreum. Significance and Impact of the Study: This study presents significant new findings with regard to the progression and causative agents of spoilage in N. norvegicus. Based on the results, we can recommend that N. norvegicus tails should be stored in a 0°C environment immediately after catch. Stored this way, the growth and spoilage activity of the microflora may be reduced significantly and an extension of shelf life might be attained.     

Diversity of cellulolytic bacteria in landfill

Nine of 37 cellulolytic bacterial isolates obtained from landfill waste could be easily differentiated on the basis of gross morphological characteristics. Four isolates were selected for further characterization and on the basis of initial results appear to be previously unidentified cellulolytic species of bacteria. An aerotolerant anaerobic, cellulolytic Clostridium and three obligately anaerobic cellulolytic Eubacterium isolates are described. The Clostridium has an unusually high pH optimum for growth of 7.7. The optimum temperature for growth is 50°C. The pH growth optimum of each of the Eubacterium isolates is around pH 7.0 while temperature optima are 37° 45° and 50°C for LFI, LF4 and LF5 respectively. Most isolates had growth optima in the thermophilic range. The ease with which apparently previously unidentified species could be isolated is a reflection of the unique and highly variable, heterogeneous environment within landfill waste.     

Bacterial metabolism in small temperate streams under contemporary and future climates

1. We examined the detailed temperature dependence (0–40 °C) of bacterial metabolism associated with fine sediment particles from three Danish lowland streams to test if temperature dependence varied between sites, seasons and quality of organic matter and to evaluate possible consequences of global warming. 2. A modified Arrhenius model with reversible denaturation at high temperatures could account for the temperature dependence of bacterial metabolism and the beginning of saturation above 35 °C and it was superior to the unmodified Arrhenius model. Both models overestimated respiration rates at very low temperatures (<5 °C), whereas Ratkowsky's model – the square root of respiration – provided an excellent linear fit between 0 and 30 °C. 3. There were no indications of differences in temperature dependence among samples dominated by slowly or easily degradable organic substrates. Optimum temperature, apparent minimum temperature, Q₁₀‐values for 0–40 °C and activation energies of bacterial respiration were independent of season, stream site and degradability of organic matter. 4. Q₁₀‐values of bacterial respiration declined significantly with temperature (e.g. 3.31 for 5–15 °C and 1.43 for 25–35 °C) and were independent of site and season. Q₁₀‐values of bacterial production behaved similarly, but were significantly lower than Q₁₀‐values of respiration implying that bacterial growth efficiency declined with temperature. 5. A regional warming scenario for 2071–2100 (IPCC A2) predicted that mean annual temperatures will increase by 3.5 °C in the air and 2.2–4.3 °C in the streams compared with the control scenario for 1961–1990. Temperature is expected to rise more in cool groundwater‐fed forest springs than in open, summer‐warm streams. Mean annual bacterial respiration is estimated to increase by 26–63% and production by 18–41% among streams assuming that established metabolism–temperature relationships and organic substrate availability remain the same. To improve predictions of future ecosystem behaviour, we further require coupled models of temperature, hydrology, organic production and decomposition.     

TEMPERATURE-GROWTH RESPONSES OF ALGAL ISOLATES FROM ANTARCTIC OASES1

Thirty-five taxa (128 clonal cultures) of Antarctic algae isolated from various habitats were assayed for growth over a range of 2–34°C. Isolates, all unialgal and two axenic, varied markedly in their temperature-growth responses. Only four taxa belonging to either the Chlamydomonadaceae or Ulotrichaceae were obligately cold-adapted and incapable of growth at ≥20°C. All isolates grew at temperatures ranging from 7.5 to 18°C, and a few were incapable of growth at ≤5°C. Over one-third of the isolates grew at 30°C, but none grew at 34°C. Percentages of cold-adapted clones correlated well with the more stable low temperature habitats. Four chlamydomonad isolates displayed optimum temperatures for growth near their maximum temperatures for growth, both temperatures being well above those of the native habitats. This temperature-growth response suggests a closer relationship to algae from more moderate thermal regions than one might have supposed. However, the ability to grow at low temperatures and the inability to grow at 34°C suggest that these Antarctic algae are cold temperature adapted. Growth capability at low in situ temperatures is considered more useful ecologically than physiologically-defined categories for algae based on their maximum temperature for growth.     

CHARACTERIZATION OF PSYCHROPHILIC OSCILLATORIANS (CYANOBACTERIA) FROM ANTARCTIC MELTWATER PONDS

Oscillatorian cyanobacteria dominate benthic microbial mat communities in many polar freshwater ecosystems. Capable of growth at low temperatures, all benthic polar oscillatorians characterized to date are psychrotolerant (growth optima > 15° C) as opposed to psychrophilic (growth optima ≤ 15° C). Here, psychrophilic oscillatorians isolated from meltwater ponds on Antarctica's McMurdo Ice Shelf are described. Growth and photosynthetic rates were investigated at multiple temperatures, and compared with those of a psychrotolerant isolate from the same region. Two isolates showed a growth maximum at 8° C, with rates of 0.12 and 0.08 doublings·d ^{? 1}, respectively. Neither displayed detectable growth at 24° C. The psychrotolerant isolate showed almost imperceptible growth at 4° C and a rate of 0.9 doublings·d ^{? 1} at its optimal temperature of ～23° C. In both photosynthesis versus irradiance and photosynthesis versus temperature experiments, exponentially growing cultures were acclimated for 14 days at 3, 8, 12, 20, and 24° C under saturating light intensity, and [¹⁴C] photoincorporation rates were measured. Psychrophilic isolates acclimated at 8° C showed greatest photosynthetic rates; those acclimated at 3° C were capable of active photosynthesis, but photoincorporation was not detected in cells acclimated at 20 and 24° C, because these isolates were not viable after 14 days at those temperatures. The psychrotolerant isolate, conversely, displayed maximum photosynthetic rates at 24° C, though photoincorporation was actively occurring at 3° C. Within acclimation temperature treatments, short‐term photosynthetic rates increased with increasing incubation temperature for both psychrophilic and psychrotolerant isolates. These results indicate the importance of temperature acclimation before assays when determining optimal physiological temperatures. All isolates displayed photosynthetic saturation at low light levels (<128 μmol·m ^{? 2}·s ^{? 1}) but were not photoinhibited at the highest light treatment (233 μmol·m ^{? 2}·s ^{? 1}). Field studies examining the impact of temperature on photosynthetic responses of intact benthic mats, under natural solar irradiance, showed the mat communities to be actively photosynthesizing from 2 to 20° C, with maximum photoincorporation at 20° C, as well as capable of a rapid response to an increase in temperature. The rarity of psychrophilic cyanobacteria, relative to psychrotolerant strains, may be due to their extremely slow growth rates and inability to take advantage of occasional excursions to higher temperatures. We suggest an evolutionary scenario in which psychrophilic strains, or their most recent common ancestor, lost the ability to grow at higher temperatures while maintaining a broad tolerance for fluctuations in other physical and chemical parameters that define shallow meltwater Antarctic ecosystems.     

ECOTYPIC VARIATION IN CYSTOCLONIUM PURPUREUM (RHODOPHYTA) SYNCHRONIZES LIFE HISTORY EVENTS IN DIFFERENT REGIONS1

Temperature and daylength responses were determined in culture for isolates of the red alga Cystoclonium purpureum (Hudson) Batters from Nova Scotia (NS, Canada), Helgoland (HE, Germany), and Roscoff (RO, France). Most isolates survived temperatures of –1.5°/–2° to 23°C, whereas 25°C was lethal. Only the RO-gametophytes died at 23°C. Optimal growth conditions were 10°–20°C in both long and short days for the NS isolates and 8°–15°C and 8°–18°C at daylengths of >12 h for the RO and HE isolates, respectively. Tetrasporophytes and gametophytes of the NS isolate reproduced at 10°–20°C in long and short days within 5 months. At lower temperatures reproduction was limited or slow. The European isolates formed tetrasporangia at 10°–20°C (HE) or 5°–l8°C(RO), spermatangia at 5°–15°C (HE) or 5°–20°C (RO), and carpospores at 5°–15°C(HE) or 10°–15°C (RO). Short days either blocked or delayed reproduction of the European isolates. The phenology of C. purpureum was studied at Helgoland and Roscoff, where similar seasonal patterns were observed. In early spring, growth was rapid and plants started to form reproductive structures. In summer, tetra-and carpospores were shed followed by degeneration of the upright axes while branched holdfasts persisted. New upright axes and juvenile plants were formed in autumn, but these remained small during the winter months. Published data indicate that the seasonal pattern at Nova Scotia is similar, although the onset of growth and reproduction is delayed until the end of spring. These observations correspond well with the results of the experiments. The life history of C. purpureum is regulated by temperature and daylength. In the eastern Atlantic, the limiting effect of short days confines growth and reproduction to spring and summer. In the western Atlantic, low winter temperatures alone bring about the same seasonal pattern. After plants have reproduced, uprights degenerate in spite of continuing favorable conditions.     

Characterization of Viable Bacteria from Siberian Permafrost by 16S rDNA Sequencing

Abstract Viable bacteria were found in permafrost core samples from the Kolyma-Indigirka lowland of northeast Siberia. The samples were obtained at different depths; the deepest was about 3 million years old. The average temperature of the permafrost is −10°C. Twenty-nine bacterial isolates were characterized by 16S rDNA sequencing and phylogenetic analysis, cell morphology, Gram staining, endospore formation, and growth at 30°C. The majority of the bacterial isolates were rod shaped and grew well at 30°C; but two of them did not grow at or above 28°C, and had optimum growth temperatures around 20°C. Thirty percent of the isolates could form endospores. Phylogenetic analysis revealed that the isolates fell into four categories: high-GC Gram-positive bacteria, β-proteobacteria, γ-proteobacteria, and low-GC Gram-positive bacteria. Most high-GC Gram-positive bacteria and β-proteobacteria, and all γ-proteobacteria, came from samples with an estimated age of 1.8–3.0 million years (Olyor suite). Most low-GC Gram-positive bacteria came from samples with an estimated age of 5,000–8,000 years (Alas suite). Received: 11 April 1996 Accepted: 8 May 1996     

Isolation of sulfate‐reducing bacteria from deep sediment layers of the pacific ocean

Bacterial populations exist at great depths in marine sediments, but little is known about the type and characteristics of organisms in this unique bacterial environment. Cascadia Margin sediments from the Pacific Ocean have deep bacterial activity and bacterial populations, which are stimulated around a gas hydrate zone (215–225 m below sea floor [mbsf]). Bacterial sulfate reduction is the dominant anaerobic process within these sediments, and the depth distribution of sulfate‐reducing activity corresponds with distributions of viable sulfate‐reducing bacteria (SRB). Anaerobically stored sediments from this site were used to isolate sulfate‐reducing bacteria using a temperature‐gradient system, elevated pressure and temperatures, different media, and a range of growth substrates. A variety of enrichments on lactate were obtained from 0.5 and 222 mbsf, with surprisingly more rapid growth from the deeper sediments. The temperature range of enrichments producing strong growth from 222 mbsf was markedly wider than those from the near surface sediment (15–45°C and 9–19°C, respectively). This presumably reflects a temperature increase in deeper sediments. Only a few of these enrichments were successfully isolated due to very slow or no growth on subculture, despite the use of a wide range of different media and growth conditions. Psychrophilic and mesophilic sulfate‐reducing isolates were obtained from 0.5 m depth. As the minimum growth temperature of the mesophile (probably a Desulfotomaculum sp.) was above the in situ temperature of 3°C, it must have been present in the sediment as spores. A larger number of isolates (23) was obtained from 222 mbsf, and these barophilic SRB were closely related (based on 16S rRNA gene analysis), but not identical to, Desulfovibrio profundus, recently isolated from deep sediments from the Japan Sea. Bacteria related to D. profundus may be widespread in deep marine sediments.     

Psychrotrophic Bacteria Isolated from a Constantly Warm Tropical Environment

Psychrotrophic bacteria are known to occur in temperate, constantly cold, and artificially cooled environments. This is the first report of their occurrence in a constantly warm (ca. 24°–35°C) tropical environment. Soil samples taken from two sites along the southeastern coastal zone of Jamaica yielded growth of psychotrophic bacteria after 3–4 weeks of enrichment culture in 1/30 strength tryptic soy broth, 20 mg L⁻¹ cycloheximide at 2°C. Growth of individual isolates at 2°C was confirmed. Isolates include aerobic and fermentative Gram-negative rods and sporeforming (Bacillus sp.) and non-sporeforming (Aureobacterium sp.) Gram-positive rods. We determined the effect of temperature on growth rate in four isolates. Strain Y1 has an unusually wide temperature range for growth, 2°–44°C, resembling that of Listeria monocytogenes. In strain R1 the optimum temperature for growth occurred unusually near the maximum temperature for growth. Strains R2 and Y2 displayed cardinal temperatures typical of known psychotrophs but appear to have evolved enhanced growth potential near the optimum temperature in response to a constantly warm environment. Received: 30 April 1997 / Accepted: 9 August 1997     

Rock phosphate solubilization by psychrotolerant Pseudomonas spp. and their effect on lentil growth and nutrient uptake under polyhouse conditions

Psychrotolerant Pseudomonas isolates (RT5RP2 and RT6RP) isolated from the rhizoplane of wild grass at 3,100 and 3,800 m above mean sea level, respectively, from Rudraprayag district of Uttarakhand (India), were found to solubilize Udaipur rock phosphate (URP). Both isolates grew at temperatures ranging from 4 to 30 °C. Kinetics of phosphate solubilization by the bacterial strains showed a nonlinear regression of the rate of P solubilization, which fitted best in the power model, and showed a declining trend across three different temperatures. Under pot culture conditions, bacterization of lentil seeds (cv. VL Masoor 507) with the psychrotolerant Pseudomonas strains when combined with URP as a sole source of phosphorus resulting in significant enhancement in P uptake of the plants, compared to the application of rock phosphate alone.