Identification and characterization of Rhodopseudomonas spp., a purple, non-sulfur bacterium from microbial mats

A species of facultative photo-organotrophic, purple, non-sulfur bacterium was isolated from mixed-species microbial mats, characterized and examined for metal tolerance and bioremediation potential. Contributing mats were na tural consortia of microbes, dominated by cyanobacteria and containing seve ral species of bacteria arranged in a laminar structure, stabilized within a gel matrix. Constructed microbial mats were used for bioremediation of he avy metals and organic chemical pollutants. Purple, non-sulfur bacteria are characteristically found in lower strata of intact mats, but their contrib uting function in mats survival and function by mediating the chemical envi ronment has not been explored. The gram-negative rod-shaped bacterium, repo rted here, produced a dark red culture under phototrophic conditions, repro duced by budding and formed a lamellar intracytoplasmic membrane (ICM) syst em parallel to cytoplasmic membrane, which contained bacteriochlorophyll a and carotenoids. This strain was found to have multiple metal resistances a nd to be effective in the reductive removal of Cr(VI) and the degradation o f 2,4,6-trichlorophenol. Based on the results obtained from morphology, nut rient requirements, major bacteriochlorophyll content, GC content, random a mplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) profile and 1 6S-rDNA phylogenetic analysis, this member of the microbial mats may be ide ntified as a new strain of the genus Rhodopseudomonas. (C) 2001 Elsevier Sc ience Ireland Ltd. All rights reserved.