Photosynthetic bacteria in meromictic lakes and stratified fjords of the Vestfold Hills, Antarctica

Abstract

Thirteen meromictic lakes and two permanently stratified fjords in the Vestfold Hills, Antarctica, were surveyed in 1983 for photosynthetic bacteria. Burton Lake and Ellis Fjord were sampled throughout the year to determine seasonal variations. Physical and chemical parameters were recorded and related to the species present. The dominant species in waters with salinities of ≤100.7 g kg^–1 were Chlorobium vibrioforme and Chlorobium limicola with populations at the O₂-H₂S interface in the range 0.3 to 6.7 × 10⁶ ml^–1. Neither of these species was found at higher salinities. Thiocapsa roseopersicina and a Chromatium sp. were found in low numbers (<10⁵ ml^–1) in most of the same waters as the Chlorobium spp. These bacterial phototrophs developed in a narrow band below the O₂-H₂S interface where both light and H₂S were available. Very low numbers (<10² ml^–1) of Rhodopseudomonas palustris were found in both oxic and anoxic waters having salinity ≤148 g kg^–1. The dominance of the Chlorobium spp. is ascribed to their more efficient maintenance metabolism during the darkness, their faster growth at low light intensities (<1 μE m^–2 s^–1) and the lack of selective filtering of incident light. The Chlorobium spp. grew well at −2°C, but not −5°C in hypersaline waters. The concentration of H₂S had no apparent effect on the development of the bacterial flora. Viable cells were found to depths of 100 m in Ellis Fjord indicating that viability in total darkness could have been maintained for periods of the order of 1700 days.