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 °C (optimum 30 °C). It tolerated NaCl up to 1 % (w/v) (optimum 0.5 %). C_18 : 1ω7c and/or C_18 : 1ω6c (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).