Competitive development of Thiocapsa roseopersicina and Chlorobium phaebacteroides in Lake Kinneret

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Abstract
The beginning of the bloom of Chlorobium phaeobacteroides in Lake Kinneret is accompanied by the occurrence of cells of Thiocapsa roseopersicina, which subsequently disappear. It was found that Thiocapsa requires relatively high light intensities (50–100 μE∙m−2∙s−1) for growth which proved to be higher than that for Chlorobium. Acetate played an important role in the growth of Thiocapsa only when the organisms were exposed to light intensities which were not optimal for photosynthesis. Optimum total sulfide concentrations for growth of Thiocapsa were found to be in the range of 1–3 mM. Considering the differential uptake of the reduced sulfur components H2S and HS−, a preference for HS− is suggested. It seems further likely that H2S inhibits growth at concentrations above 1 mM, independent of the pH. Compared with Chlorobium, favourable conditions for Thiocapsa at the beginning of the bloom period are due to low in situ concentrations of H2S, which prevent rapid development of Chlorobium.