Pelodictyon phaeoclathratiforme BU-1

Pelodictyon phaeoclathhratiforme is a green sulfur bacterium frequently observed in stratified freshwater lakes where light reaches sulfide-containing water layers; it frequently represents the dominant green sulfur bacterium in this habitat. BU 1, the type strain, was isolated from water samples of Buchensee, Germany in 1989. This lake is meromictic, that is the surface and deep waters do not mix; BU 1 was isolated from 9 m deep water. Like all green sulfur bacteria, this species is strictly anaerobic and obligately phototrophic. Photosynthetic pigments comprise mainly bacteriochlorophyll e and isorenieratene/b -isorenieratene plus small amounts of bacteriochlorophyll a. It is actually a brown color. P.phaeoclathratiforme forms net-like microcolonies and has intracellular gas vesicles. Ternary fission, which leads to the formation of ring-shaped and branched colonies, is observed at growth-limiting light intensities. Gas vesicles are proteinaceous hollow rigid structures which occur only in prokaryotic cells which are impermeable to liquid but permeable to gases. Because of their gas content, gas vesicles decrease the density of the cell and may provide neutral or even positive buoyancy if present in sufficient amounts. Like ternary fission, gas vesicles are exclusively observed in cells grown at light intensities below 5 umol photons m-2 s-1. Unlike some cyanobacteria, cells of P.phaeoclathratiforme do not attain positive buoyancy and thus are unlikely to rise to the lake surface and to leave their habitat. The capability of buoyant density regulation offers one explanation for the dominance of P.phaeoclathratiforme in many stratified lakes (modified from http://genome.jgi-psf.org/finished_microbes/pelph/pelph.home.html). (HAMAP: PELPB)