1) Sulphate reducing bacteria that can only oxidize their substrate into acetate. i.e, desulfobacter strain, desulfovibrio strain, desulfobacterium strain, desulfosarcina strain, desulfotomaculum strain. 2) Sulphate reducing bacteria that can oxidize their substrate completely to carbon dioxide. i.e. , Desulfobulbus strain, desulfomonas strain, desulfovibrio strain. 3) Dissimilatory sulphate & Bisulphate reduction. i.e, Desulfovibrio vulgaris, desulfotomaculum strain, desulfovibrio gigas, desulfovibrio desulfuricans, desulfomicrobium, desulfomonile, desulfuramonas, desulfurella, sulfurospirillum, etc. 4) Chemotrophic aerobic sulfur oxidation. i.e., thiobacillus thioparus and thiobacillus strain, pseudomonas strain. etc. 5) phototrophic anaerobic oxidation of sulfur compounds : chromatiaceae, rhodospirillaceae,etc.