Changes during Long-term Growth

Growth rate and concentrations of sulfates, sulfides, proteins and glucosamine were analyzed during long-term (over 60 days) incubation of Desulfotomaculum acetoxidans DSM 771. To imitate natural conditions, incubation was done in obligate anaerobic conditions in three series, without stirring or shaking. In the first 2–3 days of incubation (lag phase), only a decrease of the sulfate level occurred. Between days 2 and 7 of incubation (logarithmic increase phase, log phase) the growth rate and levels of proteins and glucosamine increased significantly. Simultaneously the amount of dissimilated hydrogen sulfide began to increase. Hydrogen sulfide content in parallel samples treated with lysozyme was much higher. Between days 7 and 18 a plateau ascribed to the stationary phase was observed. After 2 weeks of incubation a certain reduction of the measured substances was observed, but from days 20 to 24 the growth rate again increased (‘post-stationary’ phase). The high coefficients of correlation (for individual series 0.6735; 0.7245; 0.8217) between proteins and sulfide levels and control tests done with standards (albumin and Na2S) suggest that H2S and probably sulfides react with proteins and presumably with peptidoglycan. This could explain cumulation of sulfide and its decrease in the post-stationary phase.