Phylogeny and photoheterotrophy in the acidophilic phototrophic purple bacterium Rhodoblastus acidophilus
Norbert Pfennig isolated the first acidophilic purple bacterium over 40 years ago and named the organism Rhodopseudomonas acidophila (now Rhodoblastus acidophilus). Since the original work of Pfennig, no systematic study has been conducted on the phylogeny and carbon nutrition of a collection of strains of Rbl. acidophilus. We have isolated six new strains of Rbl. acidophilus from a Canadian peat bog. These strains, three of the original Pfennig strains and two additional putative R. acidophilus strains isolated several years ago in this laboratory, were characterized as to their pigments, phylogeny, and carbon sources supporting photoheterotrophic growth. Phototrophic cultures were either purple or orange in color, and the color of a particular strain was linked to phylogeny. As for the Pfennig strains of Rbl. acidophilus, all new strains grew photoheterotrophically at pH 5 on a variety of organic and fatty acids. However, in addition to methanol and ethanol, the new strains as well as the Pfennig strains grew on several other primary alcohols, results not reported in the original species description. Our work shows that some phylogenetic and physiological diversity exists within the species Rbl. acidophilus and supports the observation that few species of acidophilic purple bacteria appear to exist in nature.
KeywordsPurple nonsulfur bacteria Acidophiles Rhodoblastus acidophilus
This work was supported in part by grant 0950550 from the United States National Science Foundation. We thank Dr. Brian Benscoter (now of Florida Atlantic University) and Dr. Dale Vitt (Southern Illinois University) for the Canadian bog sample. We also thank Deborah O. Jung for help in preparing Figs. 1 and 2 and formatting the tables, and for helpful comments on the manuscript.
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