Photosynthetic activity and population dynamics of Amoebobacter purpureus in a meromictic saline lake

Abstract

A dense population of the purple sulfur bacterium Amoebobacter purpureus in the chemocline of meromictic Mahoney Lake (British Columbia, Canada) underwent consistent changes in biomass over a two year study period. The integrated amount of bacteriochlorophyll reached maxima in August and declined markedly during early fall. Bacteriochlorophyll was only Weakly correlated with the light intensity and water temperature in the chemocline. In the summer, bacterial photosynthesis was limited by sulfide availability. During this period the intracellular sulfur concentration of A. purpureus cells decreased. A minimum concentration was measured at the top of the bacterial layer in August, when specific photosynthetic rates of A. purpureus indicated that only 14% of the cells were photosynthetically active. With the exception of a time period between August and September, the specific growth rates calculated from CO 2 fixation rates of A. purpureus were similar to growth rates calculated from actual biomass changes in the bacterial layer. Between August and September 86% of the A. purpureus biomass disappeared from the chemocline and were deposited on the littoral sediment of Mahoney Lake or degraded within the mixolimnion. This rise of cells to the lake surface was not mediated by an increase in the specific gas vesicle content which remained constant between April and November. The upwelling phenomenon was related to the low sulfur content of A. purpureus cells and a low resistance of surface water layers against vertical mixing by wind.

Grazing of the copepod Diaptomus connexus on purple sulphur bacteria in a meromictic salt lake

“…During the study period, the production of heterotrophic bacteria exceeded that of phytoplankton and of A. purpureus (Overmann et al, 1996a; Table 1). We used the productivity values and the carbon transfer efficiency values published previously (Overmann et al, 1994;1996a;1999) to calculate the carbon flows between the various microbial compartments in Mahoney Lake ( Table 2, Data are shown for an experiment conducted in August 1993. Time 0 denotes the start of distillation of 14 CO 2 after removal of copepods from the mesocosm.…”

“…Physiologically, this has been attributed to the high sensitivity of crustacean zooplankters to toxic hydrogen sulphide (Mazumder and Dickman, 1989;. In Mahoney Lake, however, 86% of the biomass of A. purpureus entered the mixolimnion by upwelling of cell aggregates during the autumn (Overmann et al, 1994) and led to an input of 31.5 g C m ¹2 of readily degradable biomass ( Table 2, Fig. 3), which exceeded phytoplankton biomass by a factor of 130.…”

“…Data compiled or calculated from Overmann et al (1994;1996a;1999). All values are weighted for the decrease in volume of water strata with depth.…”

“…The biomass and production values of the various microorganisms were determined by standard methods as described previously (Overmann et al, 1994;1996a;1999). Production of phytoplankton was measured as carbon fixation using NaH 14 CO 3 , and the production of heterotrophic bacterioplankton by [ 3 H]-thymidine incorporation (corrected for incorporation into non-DNA macromolecules; Overmann et al, 1996a).…”

“…14 CO 2 fixation and [ 3 H]-thymidine incorporation in different size fractions were determined by filtration of lake water through 0.2 and 3 m pore size polycarbonate filters after in situ incubation of water samples. Production of A. purpureus was measured as carbon fixation using NaH 14 CO 3 and was similar to the net growth rates of the population in the chemocline (Overmann et al, 1994). The biomass of A. purpureus entering the oxic water layers by upwelling was quantified from the biomass loss from the chemocline (Overmann et al, 1994), corrected for growth during the upwelling event.…”