Obligately phototrophic Chloroflexus: primary production in anaerobic hot spring microbial mats

Microbial mats which lack cyanobacteria occur at 50° to 65° C in the sulfide-containing Mammoth Springs of Yellowstone National Park. The principal organisms within these mats are filamentous bacteria which resemble Chloroflexus aurantiacus. The incorporation of [¹⁴C]-HCO ₃ ^- into mat material depended upon both light and sulfide, and was not inhibited when complete natural light was replaced with far-red and infra-red radiation. [¹⁴C]-acetate was incorporated in a light-dependent reaction which was stimulated by, but did not require, sulfide. In situ experiments with microelectrodes demonstrated net sulfide uptake by the mat in the light, and net sulfide production by the mat in the dark, suggesting the operation of a sulfur cycle.Filamentous phototrophic bacteria isolated from the mat were incapable of sustained growth in the presence of O₂.Simultaneous exposure of cultures to light and O₂ caused degradation of bacteriochlorophyll c. The stimulation of light-dependent [¹⁴C]-HCO ₃ ^- -uptake by sulfide was more pronounced in these isolates than in strains of Chloroflexus aurantiacus.     

通过C27/C29甾烷和有机碳同位素来判断早古生代和前寒武纪的烃源岩的生物来源

在早古生代与前寒武纪的石油与源岩中,经常出现令人困惑的C29甾烷优势,而在有机地球化学中C29甾烷优势被认为是陆相有机质输入的标志。作者通过对比文献中各种海相藻类的热模拟产物分析,提出了早古生代与前寒武纪的石油与源岩中C29甾烷优势主要来源于浮游绿藻的观点,并通过C27甾烷/C29甾烷的比值提出了区分早古生代及前寒武纪石油源岩沉积环境的方法,对中国南方前寒武纪和早寒武世黑色岩系的有机地球化学分析也支持上述推断。此外,本文还提出了用有机碳同位素来进一步区分C29甾烷优势生物来源的方法。     

Pyrolysis of precambrian kerogens: Constraints and capabilities

Summary Precambrian kerogens are currently considered to be the primary candidates for the search of biochemical fossils. Degradation of kerogens by relatively mild pyrolysis techniques, such as under high vacuum, can liberate indicative structural moieties which were incorporated in, and perhaps shielded by, these solid and highly condensed, basically aromatic substances. It is necessary to observe analytical constraints (sample size and shape, temperature, pressure, time, etc.) in order to prevent an overabundant yield of secondary pyrolyzates (inter- and intramolecular rearrangements) which can prevent kerogen characterization. Potential biochemical fossils have been found in Precambrian kerogens. Demonstratable syngenetic biochemical fossils are expected after kerogen diagenesis and catagenesis is understood in sufficient detail, and when pyrolysis is augmented by multiple, improved analytical techniques.Dedicated to the Memory of H.C. Urey (1893–1981)     

DISTRIBUTION OF THE GENUS CYCLOTELLA IN RELATION TO pH IN PRECAMBRIAN SHIELD LAKES: IMPLICATIONS FOR DIATOM-INFERRED pH1

Recent research on relationships between diatoms and pH suggests that the genus Cyclotella exhibits a strong relationship with lake acidity, being almost totally absent below pH 5.5. This decline has been used as an indicator of lake acidification in paleolimnological studies. In this study C. stelligera V.H. and C. kützingiana Thwaites were abundant in Precambrian Shield lakes with pH as low as 4.5. Cyclotella comta (Ehr.) Kütz. was found in lakes of pH < 5.5, but maximum abundance was observed in lakes of pH > 5.5. Cyclotella michiganiana Skv. was found in lakes of pH < 6.0. These results indicate that the use of C. stelligera, C. kützingiana, and possibly C. comta, in paleolimnological investigations of lake acidification, should be approached with caution. These taxa may exhibit a decline in abundance with decreasing lakewater pH, but this is partially a morphometric effect not necessarily related to anthropogenic acidification.     

Stromatoporoid-grade and other sponge fossils from the upper Krol Formation of the Lesser Himalaya (India) Implications for the biotic evolution around the Precambrian-Cambrian boundary interval

Summary A study of fossils in thin sections of a sample from the uppermost Krol E Member in the Mussoorie Hills of the Lesser Himalaya, India, proves the existence of morphologically differentiated calcified sponges within the Precambrian-Cambrian boundary time interval. The sponges, described as Mussooriella kroli n.g., n.sp. and Maldeotaina composita n.g., n.sp. indicate the presence of different organization grades at the Precambrian-Cambrian interval. Mussooriella had a calcareous skeleton consisting of skeletal elements composed of an inner laminated part and a distinct peripheral layer with knobs. Maldeotaina is characterized by a stromatoporoid-grade growth pattern following a thalamid-grade pattern. The stromatoporoidgrade part of the skeletons reminds strongly on skeletal elements common in labechiid Ordovician and younger stromatoporoids. Maldeotaina also shows criteria of Early Cambrian fossils, originally described as stromatoporoids and later excluded from this group and transferred to archaeocyaths. These similarities point to an Early Cambrian age of the fossil-bearing horizon in the topmost Krol E Member. Growth cavities with crypts indicate that the sponges might have contributed to the formation of small metazoan reefs-like structures. Although the study is based on limited material and many interpretations are still tentative, a thorough documentation of the preliminary results seems reliable considering the high potential of the fossils of the upper Krol Formation important source in understanding of early metazoan differentiation.