species of budding phototrophic purple bacteria

enriched from a hot spring environment using conditions that favor growth of anoxygenic photo-trophs able to use N 2 as the sole nitrogen source for growth. Phototrophic growth rate of the bud-ding bacterium is optimal at ca. 40°C, and the maximum ~owth temperature is ca. 46°C. R. cryptolactis requires vitamin Bi2, nicotinic acid, and p-aminobenzoic acid for.optimal growth in synthetic media, and has restricted capacities in respect o pl'ototrophic carbon and nitrogen nutri-tion. Molecular nitrogen, NH~', and urea can serve as nitrogen sources; pyruvate and lactate as carbon sources. Utilization of lactate, however, is depen-dent on the presence of bicarbonate, suggesting a linkage between laeta!e photometabolism and op-eration of the Calvin reductive pentose cycle. The photopigments of R. cryptolactis, including baeterioehlorophyll a, are housed in lamellar stacks parallel to and underlying the cell mere