PubMed · 11966818
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David C White. 2002. Microbial community analysis.. https://doi.org/10.1046/j.1462-2920.2002.t01-2-00257.x
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Flagellated bacteria, such as Escherichia coli, swim by rotating thin helical filaments, each driven at its base by a reversible rotary motor, powered by an ion flux. A motor is about 45 nm in diameter and is assembled from about 20 different kinds of parts. It develops maximum torque at stall but can spin several hundred Hz. Its direction of rotation is controlled by a sensory system that enables cells to accumulate in regions deemed more favorable. We know a great deal about motor structure, genetics, assembly, and function, but we do not really understand how it works. We need more crystal structures. All of this is reviewed, but the emphasis is on function.
Biomarkers in geological samples on Earth are products derived from biochemical precursors (i.e., natural products) by reductive and oxidative alteration processes (e.g., cholestanes from cholesterol). Generally, lipids, pigments, and some biomembranes are preserved best over longer geological times, and labile compounds such as amino acids, sugars, etc. are useful biomarkers for recent times. Thus, the detailed characterization of biomarker composition permits the assessment of the major contributing species of extinct and/or extant life. Nonbiomarkers and abiogenic organic compounds are also discussed. In the case of the early Earth, work has progressed to elucidate biomarker structures and carbon isotopic signals preserved in ancient sedimentary rocks. In addition, the combination of bacterial biochemistry with the organic geochemistry of contemporary and ancient hydrothermal ecosystems permits the modeling of the nature, behavior, and preservation potential of primitive microbial communities. This approach entails combined molecular and isotopic analyses to characterize lipids and biopolymers produced by cultured bacteria (representative of ancient strains) and to test a variety of culture conditions that affect their biosynthesis processes. In regards to Mars, the biomarkers from lipids and biopolymers would be expected to be preserved best if life flourished there during its early history (3.5-4 x 10(9) years ago). Both oxidized and reduced products would be expected. This is based on the inference that hydrothermal activity occurred during that time, with the concomitant preservation of biochemically-derived carbonaceous matter. Known biomarkers (i.e., as elucidated for early terrestrial samples and for primitive terrestrial microbiota) as well as novel, potentially unknown compounds, should be characterized.
A laboratory experiment was performed to test whether differences in nutrient and energy demands between picophytoplankton and heterotrophic bacteria can explain the apparent inverse biomass relationship between these organisms in lakes along gradients of organic carbon and nutrients. Growth rates and final yield of cells were analyzed in crossed gradients of glucose and phosphate. Concentrations of phosphate (10, 25, and 60 microg P L(-1)) and glucose (0, 0.3, and 3 mg C L(-1)) were used in all possible combinations giving 9 different treatments. Heterotrophic bacteria had higher maximum growth rates in all treatments and became larger than picophytoplankton in many treatments. The variance in abundance of heterotrophic bacteria between treatments could almost completely be explained by the combined effects of glucose and P. In treatments where carbon limitation slowed down the growth of heterotrophic bacteria, picophytoplankton became abundant and these organisms showed a positive response to P in combination with a negative response to glucose. The negative effect of glucose on picophytoplankton is suggested to be indirect and caused by competition with bacteria that are favored by organic C. The results suggest that competition for phosphate between phytoplankton and bacteria is not size-dependent, that heterotrophic bacteria are superior competitors for P, and that organic C produced by picophytoplankton was of minor importance for heterotrophic bacteria.