Exam 2 Study Guide (Page 11)

Can be measured by: Chemical assay Measure concentrations of precursors and products of reaction (i.e., lactate fermentation) Direct measure of these compounds Less sensitive Radioisotope Measure of photoautotrophy--amount of CO2 incorporated during photosynthesis Use radiolabel CO2 and measure its uptake More sensitive FISH-MAR Incorporate both radioactivity (activity) and FISH (identity) for analysis of sample Powerful technique that can be used from either a microbial community or pure culture Microelectrodes Can measure pH, O2, N2O, CO2, H2, or H2S Used extensively in study for microbial activity in nature Microbial mats Layered microbial communities Anoxygenic phototrophic bacteria on top, chemoorganotrophs in lower layers (sulfate-reducing) Microbe mats are often developed in hot springs and marine intertidal zones Stable Isotopes Many elements can exist as different isotopes due to present of different neuron number Stable isotopes are not radioactive and are metabolized differently by microbes Most useful is carbon (CO2) and sulfur (SO42-); C12 mostly and C13; S32 and some S34 Isotopic Fractionation: Cells preferentially use the lighter isotope Can use to trace microbe transformation in nature (like labeling) Determine the biological history of a sample Calculate the ratio of C13:C12 to determine whether sample was made from biological vs. geological origin; samples that are lighter come from biological sources Methane is light = methanogenic Archaea Calculate the ratio of S34:S32 for monitoring the sulfate-reducing bacteria in nature Igneous rock, lunar sulfides are heavy; sedimentary sulfide is lighter Microbial Ecosystem Biodiversity: The types of microbes that are present Microbial activity: Microorganisms metabolism and their metabolic products Microbial ecosystem involves: Microbial interaction Transfer of nutrients to one another, to larger organisms and to the atmosphere Balance nutrient cycles: exchange of carbon, nitrogen, phosphorus, sulfur, iron and magnesium