Effect of H2S on heterotrophic substrate uptake, extracellular enzyme activity and growth of brackish water bacteria

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Abstract
In some parts of the Baltic Sea, establishment of anoxia, H2S accumulation and reaeration of the water column are common processes which have a bearing on the heterotrophic microbial community. The influence of these conditions on natural aerobic populations was studied in 24 h batch cultures. Measured parameters were: saprophyte number and total number of bacteria, active bacteria (leucine microautoradiography), heterotrophic substrate uptake (14C labelled glucose, leucine, lactate) extracellular enzyme activity (.beta.-glucosidase, peptidase) and growth of bacteria (3H-methyl thymidine incorporation). Anoxia established by N2 had a minor effect on these parameters and values approximated those from the oxic control within the incubation period. Addition of H2S led immediately to a strong but variable reduction in all the activity measurements and recovery was weak when H2S conditions were maintained over the experimental period. Re-aeration after after 12 h of H2S incubation caused a progressive increase of the activity measurements which then by far exceeded those from the continuously oxic control. An exception was peptidase, which recovered only slowly after H2S depletion. Short-term application of H2S caused clear changes in the metabolic and community structure of the originally aerobic bacterial population, which were also documented by a reduction of the spectrum of morphological cell characters. Cells which survived H2S stress developed vigorously after H2S depletion. Values of bacterial production calculated from increases in active bacterial numbers and from thymidine uptake showed the same tendency; however, their absolute values differed considerably. This discrepancy may indicate that after H2S stress many of the surviving cells were reactivated, but only a fraction of these started reproduction.