Fatty Acids, Antibiotic Resistance, and Deoxyribonucleic Acid Homology Groups of Bradyrhizobium japonicum

Abstract

The fatty acid compositions and multiple antibiotic resistance patterns of 32 strains of Bradyrhizobium japonicum correlated with two major deoxyribonucleic acid homology groups. In group I, the fatty acid composition was 1.3% 16:l cis9 acid, 3.6% 16:lC acid, 8.8% 16:O acid, 1.2% 19:0 cyclopropane acid, and 81.2% 18:l acid. Group I1 contained 0.5% 16:lC acid, 11.1% 16:O acid, 0.8% 17:O cyclopropane acid, 24.7% 19:O cyclopropane acid, and 62.3% 18:l acid. Group I strains were susceptible to rifampin (500 pglml), tetracycline (100 pglml), streptomycin (100 pg/ml), chloramphenicol (500 pg/ml), erythromycin (250 pglml), carbenicillin (500 pg/ml), and nalidixic acid (50 pg/ml), whereas group I1 strains were resistant to these antibiotics. Both groups were resistant to trimethoprim (50 pg/ml) and vancomycin (100 pglml).Bradyrhizobium japonicum (Jordan 1982) (formerly Rhizobium japonicum) is the slow-growing symbiont of soybeans. This species is comprised of two highly divergent taxonomic groups which should be phenotypically distinguishable. The deoxyribonucleic acid (DNA)-DNA hybridization studies of Hollis et al. (8) established DNA homology groups I, Ia, and 11. These groups were characterized with respect to acidic extracellular polysaccharide composition and phenotypic ex planta nitrogenase expression. Groups I and Ia were reported to be quite distinct from DNA homology group I1 according to both of these criteria (9). Using some of the same strains, Stanley et al. (21) characterized the DNA nucleotide sequence divergences in and proximal to known symbiotic genes and concluded that strains of B . japonicum comprise two symbiotic genotypes (sTI and sTII) consistent with separate species designations.Whole-cell fatty acid profiles of strains grown under standardized conditions have been used for identification (1, 4,18) and classification of many bacteria (10, 17), but not in the genus Bradyrhizobium. Pankhurst et al. (20) correlated rifampin resistance in some slow-growing rhizobial strains with in vitro nitrogenase activity. This observation, together with that of Huber et al. (9) that only DNA homology group I1 strains express nitrogenase in vitro, suggested to us that patterns of antibiotic resistance might also distinguish the groups. In this paper we report that whole-cell fatty acid profiles correlate with DNA homology groups I and I1 of Hollis et al. (8) and that patterns of high-level resistance to antibiotics distinguish the two DNA homology groups. MATERIALS AND METHODSBacterial strains. All USDA strains were obtained from H. H. Keyser and D.Weber, U. S. Department of Agriculture (USDA), Beltsville, Md.; strain ATCC 10324 was obtained from the American Type Culture Collection, Rockville, Md.; strains 5631, 5633, D193, D209, THA6, and 8' were obtained from G. H. Elkan, North Carolina State University, Raleigh; and strains 61A.50 and 61A76 were obtained from S. Smith, Nitragin Co., Milwaukee, Wis. Strains that exhibit rifampin resistance and tetracycline resistance were purified by streaking onto a mediu...

The Genus Nocardiopsis Represents a Phylogenetically Coherent Taxon and a Distinct Actinomycete Lineage: Proposal of Nocardiopsaceae fam. nov.

“…Fatty acid methyl esters were obtained from wet biomass (ca. 40 mg) by saponification, methylation, and extraction (15). The fatty acid methyl ester mixtures were separated by using a model 5898A microbial identification system apparatus (Microbial ID, Newark, Del.).…”

Edaphobacter modestus gen. nov., sp. nov., and Edaphobacter aggregans sp. nov., acidobacteria isolated from alpine and forest soils

“…Forty milligrams (wet weight) of cells was scraped from Petri dishes and fatty acid methyl esters were extracted using the method of Miller (1982) and Kuykendall et al (1988). Analyses were performed by the Deutsche Sammlung von Mikroorganismen und Zellkulturen (DSMZ).…”

Paenibacillus segetis sp. nov., isolated from soil of a tropical rainforest

“…Polar lipids were extracted and examined on 10Â10 cm TLC Silica gel 60 F 254 plates (Merck) (Minnikin et al, 1984;Ruan, 2006). Total cellular fatty acid methyl esters were prepared and determined by using GC/ MS (model GC-2010; Shi-madzu) (Kuykendall et al, 1988). Isoprenoid quinones were purified (Xu et al, 2007) by TLC and analysed by HPLC (Komagata & Suzuki, 1987).…”