ABSTRACT
Nearly complete and short partial 16S rRNA sequences were derived from PCR-amplified ribosomal DNAs of Bradyrhizobium japonicum USDA 136 and USDA 110 and five strains of bacteriochlorophyll-synthesizing bacteria isolated from stem nodules of Aeschynomene indica and other Aeschynomene species growing in different geographic regions, including India, The Philippines and North America. We confirmed that the five stem-nodulating strains examined synthesize bacteriochlorophyll a, and the absorption spectra of methanol-extracted cells contained a major absorbance peak at 770 nm. Strains isolated on different continents and from different Aeschynomene species were found to be phylogenetically homogeneous and exhibited levels of sequence similarity of more than 99%. The bacteriochlorophyll-synthesizing rhizobia, Bradyrhizobium japonicum, Blastobacter denitrificans, Afipia felis, and Rhodopseudomonas palustris exhibited levels of sequence similarity of 97% or greater and belong to a distinct line of descent within the alpha-2 subdivision of the Proteobacteria. Variable regions between positions 995 and 1045 provide potential target sites for design of a probe that is able to distinguish the photosynthetic rhizobia from closely related taxa.
ABSTRACT
Rhizobium strain BTAi 1, which nodulates both stems and roots of Aeschynomene indica L., formed bacteriochlorophyll and photosynthetic reaction centers resembling those of purple photosynthetic bacteria when grown aerobically ex planta under a light-dark cycle. Bacteriochlorophyll formation was not observed under continuous dark or light growth conditions. The amount of pigment formed was similar to that previously found in aerobic photosynthetic bacteria. Stem nodules appear to fix nitrogen photosynthetically, as illumination of A. indica stem nodules with near-infrared light resulted in an enhanced rate of acetylene reduction. Near-infrared light did not enhance acetylene reduction when either A. indica or soybean root nodules were illuminated. The BTAi 1 isolate can be differentiated from members of the family Rhodospirillaceae by several criteria.
Subject(s)
Nitrogen Fixation , Photosynthesis , Adenosine Diphosphate/pharmacology , Adenosine Triphosphate/physiology , Ammonia/physiology , Bacteria/enzymology , Bacteria/growth & development , Bacteria/metabolism , Cell-Free System , Ecology , Enzyme Repression , Ferredoxins/analysis , Flavoproteins/analysis , Nitrates/physiology , Oxidation-Reduction , Oxidoreductases/metabolism , Oxygen/physiology , Plant Proteins/analysisABSTRACT
Purified outer segments of bovine rods exhibit phosphodiesterase activity against adenosine and guanosine cyclic 3',5'-monophosphates (cyclic AMP and cyclic GMP). The enzyme hydrolyzed cyclic GMP more rapidly than cyclic AMP at low substrate concentrations. The presence of high phosphodiesterase activity in this highly specialized organelle suggests that this enzyme may function in control of cyclic nucleotide concentration during visual excitation or adaptation.
