Confocal laser scanning microscopy as a tool to determine cyanobacteria biomass in microbial mats

We have developed a method based on confocal laser scanning microscopy for detection and quantification of cyanobacteria from the Ebro Delta microbial mats. Cyanobacteria play a major role as primary producers in microbial mats; it is difficult, however, to apply classical methods to estimate their biomass because they establish strong interactions with detritic particles. The protocol described here allows the localization of individual cells or filaments with micrometre precision without the need to either manipulate or stain the samples. This method is suitable for studying biomass ' in situ ' in microbial mats.     

Optimization of growth operational conditions for CO2 biofixation by native Synechocystis sp.

BACKGROUND: A fundamental step in assessing the viability of a CO₂ biofixation system based on microalgae is to identify the maximum CO₂ biofixation yield that can be achieved for this microorganism when it is cultivated under optimum operational growth conditions. Response surface methodology was applied to determine optimum culture conditions for CO₂ biofixation by a recently isolated freshwater cyanobacterium Synechocystis sp. The strain was cultivated in a 1 L bubble column photobioreactor, in semicontinuous mode. RESULTS: Statistical analysis showed that temperature (from 22 to 39 °C), pH (from 7.2 to 8.8) and light intensity (from 928 to 2272 µE m^?2 s^?1), in addition to some of their interactions, had a significant effect on CO₂ biofixation. An optimum CO₂ biofixation rate of 2.07 gCO₂ L^?1culture day^?1 was found within the experimental region, at an average light intensity 686 µE m^?2 s^?1, pH 7.2 and temperature 35.3 °C. CONCLUSIONS: Based on these results, it is concluded that Synechocystis sp. presents a good tolerance to both high temperature and light intensity, characteristics which facilitate its application in outdoor CO₂ biofixation systems. Copyright © 2011 Society of Chemical Industry     

Production of Antioxidants by Anabaena PCC 7119 and Evaluation of Their Protecting Activity Against Oxidation of Soybean Oil

The objective of this work was to study the occurrence of antioxidant compounds in the cyanobacterium Anabaena PCC 7119, as part of our research on new antioxidants for use in food preservation. Anabaena PCC 7119 was grown under light intensities of 100 (I), 200 (II) and 300 (III) μMoles of photons/m².seg. Biomass was obtained in the exponential and stationary phases and was extracted with methanol. Extracts were fractionated on a charcoal column and the fractions were tested for antioxidant activity using thin layer chromatography β-carotene bleach test. The higher biomass production was obtained with light intensity II. Antioxidant activity was found in the extracts of all growth phases for light intensities I, and II but not for III. The ability of the extracts to prevent soybean oil oxidation was also tested. Biomass extracts obtained from both exponential and stationary phases under conditions I and II displayed antioxidant and synergistic activities in soybean oil. Moreover, when tested in oil used in frying potatoes, the extracts displayed heat stability. The extract obtained from biomass III did not show such activities suggesting that excess light decreased the production of antioxidant compounds. Our results demonstrate the potential of biotechnology of cyanobacteria in the production of new antioxidants for food preservation.     

Redundant pathways of sunscreen biosynthesis in a cyanobacterium

Route of the sun block: according to empirical evidence, sun-screening mycosporine-like amino acids (MAAs) in Eukarya originate from the shikimic acid pathway, whereas in cyanobacteria, biosynthesis of the MAA shinorine reportedly occurs through the pentose phosphate pathway. However, gene deletion shows that the cyanobacterium Anabaena variabilis ATCC 29143 does not biosynthesise shinorine exclusively by this route.     

Alum and Lime-Alum Removal of Toxic and Nontoxic Phytoplankton from the Nile River Water: Laboratory Study

No phytoplankton should be present in treated drinking water because of its potential for bad odor and toxins that may pose hazards to animals and humans upon consumption. This study describes the efficiency of alum and lime-alum treatments for removing phytoplankton from the Nile river water used as a source of drinking water in Egypt. The results showed that alum could not precipitate all phosphate nor coagulate bloom forming cyanobacteria present in the water sample. On the other hand, lime-alum treatment precipitated much more phosphate than alum, and coagulated all phytoplankton present in the water samples including those that could not be coagulated by alum. Furthermore, lime-alum treatment did not change the pH of the water during all the experiment period. Hence, it is suggested that lime-alum be used instead of alum during water treatment processes in Egypt.     

Risk‐based approach for assessing the effectiveness of flow management in controlling cyanobacterial blooms in rivers

Cyanobacterial blooms present significant water quality problems worldwide. Flow management is considered to be one of the most promising approaches for combating the cyanobacterial bloom problem in rivers. In this paper, a new method for evaluating the effectiveness of flow management strategies in reducing the risk of cyanobacterial blooms is developed and applied to the River Murray at Morgan, South Australia. As stratification has been shown to be a necessary condition for significant growth of certain cyanobacteria species, the method uses estimates of the probability that stratification events of various durations will occur in conjunction with estimates of population growth during stratified conditions to determine the probability that blooms of various magnitudes will occur. The results of the case study indicate that the probability that blooms of the cyanobacterium Anabaena circinalis exceeding 15 000 cells/ml will occur in any given year under summer entitlement flow conditions is 11.7%, which is in excellent agreement with results obtained using a Poisson–Bayesian approach applied to 17 years of historical data of cell densities of Anabaena circinalis at the study site. The results obtained also indicate that increasing inflows into South Australia by 10 000 Ml/day, which is the maximum achievable increase given current operational constraints, would not have a significant impact on the occurrence of blooms exceeding 15 000 cells/ml. An additional flow of 19 900 Ml/day into South Australia would be required to reduce the probability of occurrence of blooms exceeding 15 000 cells/ml to 0.01%. Copyright © 2004 John Wiley & Sons, Ltd.     

Planktonic interactions with an austral bias: Implications for biomanipulation

The conceptual model of trophic structure in a typical north temperate lake that underlies attempts at biological manipulation to improve water quality is reviewed in relation to the trophic structure and community composition of planktonic food webs in New Zealand and Australian lakes. New Zealand's relatively simple food webs are characterized by an absence of obligate piscivores and few vertebrate and invertebrate planktivores; manipulation of fish stock to improve water quality has not been attempted. The largest crustacean zooplankton in Australasia, and potentially the most effective grazers of phytoplankton, are Daphnia carinata and calanoid copepods (Boeckella spp.). Their potential capacities to remove algae and colonial cyanobacteria (Microcystis, filamentous forms) from waterways are discussed in relation to colony size and concentration, toxicity, selectivity, and digestibility. The potential of D. carinata to suppress rates of increase in phytoplankton biomass may be lowered by its sensitivity to crowding and starvation, and its susceptibility to predation by fish. Decisions to use biomanipulation as a management tool to improve water quality should be based on the results of a whole lake study and take into consideration relevant obligations to preserve the biodiversity of native species, and curb the spread and dominance of exotic species. Programmes that are based on reductions in biomass of planktivorous fish should be complemented by control of nutrient loads (integrated management).     

Modelling suppression of cyanobacterial blooms by flow management in a lowland river

Growth and dominance of the cyanobacterium Anabaena circinalis in weir pools of the Barwon–Darling River, Australia, are related to persistent vertical thermal stratification between October and March, when discharge is low. We determined critical velocities and discharges required to suppress bloom formation at three sites, and modelled the occurrence of sub‐critical discharges in order to predict the frequency of blooms under different management scenarios. Our model suggests that the frequency of blooms was about double that expected under near‐natural flows (without major impoundment or water extraction) for 1990–2000. Flow management, through Environmental Water Provisions that limit water extraction when river levels are low, has been in place since July 2000. Our model suggests that these provisions are unlikely to have had an effect on bloom frequency for 2000–2003. In the longer term, however, they could reduce bloom frequency at some sites by up to one‐third. Copyright © 2006 John Wiley & Sons, Ltd.