BS 375 Lecture Notes - Sulfolobus, Phototroph, Sulfur Dioxide
15 Jan 2023
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N2 fixation by free-living bacteria: aerobic bacterial species: azotobacter, anaerobic bacterial species: clostridium. Symbiosis with legume crops e. g. gram, lentil, beans. Symbiosis with non-legume crops: alder tree infected with actinomycetes frankia sp. According to an estimate 5-10 times more nitrogen is fixed symbiotically than non-symbiotically in free living bacteria. It makes about 1% of dry weight of a bacterial cell. Sulfur (s) is the 10th most abundant element in earth"s crust. Sulfur is the major form assimilated by microbes and plants. Sulfur is cycled between oxidation states of sulfates and sulfides. Sulfur is released through volcanic activity of so2 and h2s then becomes dissolved in water. Sulfur originates from rocks, oceans, lakes and swamps. Sulfur exists in the elemental form and as hydrogen sulfide gas, sulfate, and thiosulfate. Plants and many microbes can assimilate only so4 and animals require an organic source - amino acids: cystine, cysteine, and methionine. Bacteria convert environmental sulfurous compounds into useful substrates.
