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Appl. Environ. Microbiol., Sep 1996, 3251-3258, Vol 62, No. 9
J Overmann, JT Beatty and KJ Hall
In meromictic Mahoney Lake, British Columbia, Canada, the heterotrophic
bacterial production in the mixolimnion exceeded concomitant primary
production by a factor of 7. Bacterial growth rates were correlated neither
to primary production nor to the amount of chlorophyll a. Both results
indicate an uncoupling of bacteria and phytoplankton. In the chemocline of
the lake, an extremely dense population of the purple sulfur bacterium
Amoebobacter purpureus is present year round. We investigated whether
anoxygenic phototrophs are significant for the growth of aerobic
bacterioplankton in the overlaying water. Bacterial growth rates in the
mixolimnion were limited by inorganic phosphorus or nitrogen most of the
time, and the biomass of heterotrophic bacteria did not increase until, in
autumn, 86% of the cells of A. purpureus appeared in the mixolimnion
because of their reduced buoyant density. The increase in heterotrophic
bacterial biomass, soluble phosphorus concentrations below the detection
limit, and an extraordinarily high activity of alkaline phosphatase in the
mixolimnion indicate a rapid liberation of organically bound phosphorus
from A. purpureus cells accompanied by a simultaneous incorporation into
heterotrophic bacterioplankton. High concentrations of allochthonously
derived dissolved organic carbon (mean, 60 mg of C(middot)liter(sup-1))
were measured in the lake water. In Mahoney Lake, liberation of phosphorus
from upwelling purple sulfur bacteria and degradation of allochthonous
dissolved organic carbon as an additional carbon source render
heterotrophic bacterial production largely independent of the
photosynthesis of phytoplankton. A recycling of inorganic nutrients via
phototrophic bacteria also appears to be relevant in other lakes with
anoxic bottom waters.
Copyright © 1996, American Society for Microbiology
Purple Sulfur Bacteria Control the Growth of Aerobic Heterotrophic Bacterioplankton in a Meromictic Salt Lake
Department of Microbiology and Immunology and Westwater Research Centre, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z3
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