Isolation and characterization of the N₂-fixing marine photosynthetic bacterium<i>Rhodopseudomonas marina</i>, variety<i>agilis</i>

Abstract

Rhodopseudomonas marina/agilis was enriched from a natural microbial mat by using conditions that favor growth of anoxygenic photoheterotrophs able to fix N2 rapidly. The isolated bacterium grows more readily on fructose or mannitol than on organic acid carbon sources, requires preformed biotin and thiamine as growth factors, and is extraordinarily motile; growth occurs up to a temperature of approx. 44°C. The photosynthetic pigments of R. marina/agilis are housed in intracytoplasmic lamellar membranes which show the in vivo absorbance characteristics of bacteriochlorophyll a and carotenoids of the normal spirilloxanthin series. In common with other non-sulfur purple bacteria, R. marina/agilis can also grow as an aerobic heterotroph in darkness. Under these conditions, photopigment synthesis is severely repressed. R. marina/agilis requires 1–5% NaCl for optimal growth, and cells grown on N2 showed nitrogenase activity of >1000 nmol acetylene reduced h/mg dry wt.