Genetic Recombination in Rhodopseudomonas capsulata

Abstract

A system for genetic exchange in Rhodopseudomonas capsulata has been discovered. Each genetic marker thus far examined can be transferred, and many strains of Rps. capsulata can participate in genetic exchange. The mechanism of gene transfer seems unlike that of any previously described bacterial system, since genes can be transferred by cell-free filtrates, but the vector is resistant to deoxyribonuclease and has a sedimentation constant of about 70 S.Nonsulfur purple photosynthetic bacteria manifest a remarkable range of metabolic plasticity, especially in regard to alternative modes of energy conversion. Certain species, particularly of the genus Rhodopseudomonas, grow rapidly, and in recent years such organisms have been increasingly used in studies on energy conservation processes, membrane formation, and metabolic regulation (1-3). Although biochemical mutants have been used in some of these researches, genetic approaches to elucidation of mechanisms have not been possible hitherto owing to our ignorance of genetic exchange processes in the nonsulfur purple bacteria. This report describes the discovery of a genetic recombination system in Rhodopseudomonas capsulata. The genetic transfer appears to be mediated by a novel vector. MATERIALS AND METHODSRhodopseudomonas capsulata, strain "St Louis," and the strains derived from it (Z-1, MI, and M5) have all been described (4); Rps. capsulata, strain KB1 was obtained from S. (n) Kaplan. Strains B6, B10, and H9 were isolated from pond and soil samples by standard enrichment techniques.The latter three isolates have been tentatively identified as Rps. capsulata on the basis of pigmentation, cell morphology, and especially the characteristic "zig-zag" arrangement of cells in chains.The medium used throughout was composed of 0.3% Bactopeptone and 0.3% Bacto yeast extract in deionized water; for preparation of solid media, either 0.6 or 1.2% Bacto-agar was used.Photosynthetic growth was achieved in screw-cap tubes filled to capacity; these were incubated at 350 and illuminated by a bank of three 60-watt lumiline bulbs (General Electric) at a distance of about three inches (7.62 cm). First, a rifampicin-resistant mutant and a streptomycinresistant mutant were selected from each strain. Media were inoculated with pairs of strains to be tested, one member of each pair bearing the streptomycin-resistance marker, the other, refampicin-resistance. After several generations of mixed growth, the frequency of simultaneous resistance to streptomycin and rifampicin was determined and compared to the same frequency measured in singly inoculated control cultures. This procedure revealed a pair of strains, H9 and B10, that consistently gave significantly more rifampicinand streptomycin-resistant colony-forming units (CFU) than would be expected from the frequency of doubly resistant colony-forming units in the control cultures (Table 1)

Global occurrence and heterogeneity of the Roseobacter-clade species Ruegeria mobilis

“…Gene transfer agents have first been described in Rhodobacteraceae (Marrs, 1974) and are widespread within the family (Biers et al, 2008;Huang et al, 2011;Thole et al, 2012). This specific gene transfer agent has been found in all to-date sequenced Roseobacter genome sequences, but strain HTCC1062 (Zhao et al, 2009).…”

Gene transfer agent (GTA) genes reveal diverse and dynamic Roseobacter and Rhodobacter populations in the Chesapeake Bay

“…An unusual bacteriophage-like vehicle of genetic exchange known as a gene transfer agent (GTA) was first reported in the purple non-sulfur bacterium Rhodobacter capsulatus (Marrs, 1974). GTA is a small phage-like particle released by the bacteria, and each particle contains a random ca.…”

Combined actions of multiple hairpin loop structures and sites of rate-limiting endonucleolytic cleavage determine differential degradation rates of individual segments within polycistronic puf operon mRNA

“…Consistent with this notion is the finding that all strains containing plasmids that have internal deletions in the RC-coding region synthesize RNA species about 350 to 400 bp longer than the puf mRNA species terminated at the hairpin loops 3' to pugX. A discrete band longer than 2.7 kb was not observed with the 350-bp ApaI-KpnI fragment probe in RNA isolated from wild-type R. capsulatus B10 (16) (Fig. 4).…”