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Chapter 41 : Sulfur Cycling
Microorganisms of the S cycle are extremely diverse. The anaerobic sulfate-reducing bacteria (SRB), which are unique physiologically and genetically, are represented by several genera, most of which were discovered in the last 20 years. Chemolithotrophic S oxidation is mediated aerobically by colorless S bacteria, some purple S bacteria, and SRB. For enumeration, isolation, and rate measurements, it is important to process samples quickly after they are obtained and to maintain samples near ambient temperatures. Rates of SO4 2- reduction have become routine measurements in studies of the biogeochemistry of anoxic aquatic environments. SRB are readily isolated from many environments, including freshwater and salt water, soils, oil-bearing shales and strata, intestinal contents, sewage, and paper mill effluent. In recent years, molecular methods based on PCR, gene cloning, and hybridization probes have been developed to examine natural populations of bacteria directly without cultivation. Fluorescence in situ hybridization (FISH) is widely used for detection, identification, and quantification of microorganisms in the environment; the analysis of sulfur-oxidizing bacteria gives particularly interesting examples for FISH applications. Sulfide is produced from degradation of sulfur-containing organic matter and by dissimilatory sulfate reduction. Microbial metabolism of sulfide competes with chemical oxidation, either by O2 or Fe2+. Cultivation and enumeration of sulfur oxidizers are most successful in CO3 2- buffered media. High-performance liquid chromatography with fluorometric detection can also be used to measure oxidized and reduced S species.
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- Denaturing Gradient Gel Electrophoresis