Isolation and Physiological Characterization of Autotrophic Sulphur Bacteria Oxidizing Dimethyl Disulphide as Sole Source of Energy

Abstract

The isolation of a number of strains of bacteria able to grow on dimethyl disulphide and dimethyl sulphide as sole source of energy is described. The isolates came from diverse habitats, including soil, peat, marine mud and a freshwater pond. The isolates were morphologically and physiologically best described as thiobacilli, capable of growth as Calvin cycle autotrophs on inorganic sulphur compounds, methylated sulphides or thiocyanate. They could not grow heterotrophically or methylotrophically. One isolate (E6) was examined in detail. Substrate oxidation kinetics indicated that methanethiol, sulphide, formaldehyde and formate, but not dimethyl sulphide, could be implicated as intermediates in dimethyl disulphide metabolism. Apparent K s values for the oxidation of dimethyl disulphide and methanethiol were 2.5 and 3·2 μm respectively. Growth yields in chemostat culture on dimethyl disulphide with and without thiosulphate indicated that energy conservation was probably coupled to the oxidation of formaldehyde and sulphide (derived from dimethyl disulphide via methanethiol) to CO2 and sulphate. Maximum growth yield (Y max) on dimethyl disulphide was 17 g cell-carbon per mol of dimethyl disulphide. At one dilution rate (0·078 h−1), the biomass of a culture limited by dimethyl disulphide increased when thiosulphate was also supplied, indicating a thiosulphate-dependent yield of 2·45 g cell-carbon mol−1. This is the first demonstration of the isolation of organisms into pure culture that are capable of growth on dimethyl disulphide as sole energy substrate, and of degrading it completely to CO2 and sulphate.