Rhizobium lemnae sp nov., a bacterial endophyte of Lemna aequinoctialis

Bacterial strain L6-16(T) was isolated from Lemna aequinoctialis. Cells were Gram-stain-negative, rod-shaped and motile with monopolar flagella. The phylogenetic analysis of its nearly complete 16S rRNA gene sequence revealed that strain L6-16(T) was a member of the genus Rhizobium. Its closest relative was Rhizobium tarimense PL-41(T) with a 16S rRNA gene sequence similarity value of 98.3 %. Sequence similarity analysis of the housekeeping recA and atpD genes showed low levels of sequence similarity (<93.9 %) between strain L6-16(T) and other species of the genus Rhizobium. Strain L6-16(T) was able to grow between pH 5 and 11 (optimum 7.0) and at temperatures ranging from 20 to 41 degrees C (optimum 30 degrees C). It tolerated NaCl up to 1 % (w/v) (optimum 0.5 %). C-18:1 omega 7c and/or C-18:1 omega 6c (summed feature 8; 79.5%) were found as predominant cellular fatty acids. The DNA G+C content of strain L6-16(T) was 58.1 mol% (T-m). Based on low levels of DNA DNA relatedness, strain L6-16(T) was distinct from members of phylogenetically related species including R. tarimense PL-41(T) (38.3 +/- 0.8%), Rhizobium rosettiformans W3(T) (6.9 +/- 0.4%) and Rhizobium pseudoryzae J3-A127(T) (12.3 +/- 0.6 %). Strain L6-16(T) was unable to nodulate the roots of Phaseolus vulgaris, and nodC and nifH genes were not detected. The results obtained from phylogenetic analyses, phenotypic characterization and DNA-DNA hybridization indicated that strain L6-16(T) represents a novel species of the genus Rhizobium, for which the name Rhizobium lemnae sp. nov. is proposed. The type strain is L6-16(T) (=NBRC 109339(T) =BCC 55143(T)).