Rhizobium paknamense sp nov., isolated from lesser duckweeds (Lemna aequinoctialis)

A Gram-stain-negative, rod-shaped bacterium was isolated and designated strain L6-8(T) during a study of endophytic bacterial communities in lesser duckweed (Lemna aequinoctialis). Cells of strain L6-8(T) were motile with peritrichous flagella. The analysis of the nearly complete 16S rRNA gene sequence indicated that strain L6-8(T) was phylogenetically related to species of the genus Rhizobium. Its closest relatives were Rhizobium borbori DN316(T) (97.6 %), Rhizobium oryzae Alt 505(T) (97.3 %) and Rhizobium pseudoryzae J3-A1 27(T) (97.0 %). The sequence similarity analysis of housekeeping genes recA, glnll, atpD and gyrB showed low levels of sequence similarity (<91.5 %) between strain L6-8(T) and other species of the genus Rhizobium with validly published names. The pH range for growth was 4.0-9.0 (optimum 6.0-7.0), and the temperature range for growth was 20-45 degrees C (optimum 30 degrees C). Strain L6-8(T) tolerated NaCl up to 2 % (w/v) (optimum 1 % NaCl). The predominant components of cellular fatty acids were C-19:0 cyclo omega 8c (31.32 %), summed feature 8 (C-18:1 omega 7c and/or C-18:1 omega 6c; 25.39 %) and C-16:0 (12.03 %). The DNA G + C content of strain L6-8(T) was 60.4 mol% (T-m). nodC and nifH were not amplified in strain L6-8(T). DNA-DNA relatedness between strain L6-8(T) and R. borbori DN316(T), R. oryzae Alt505(T) and R. pseudoryzae J3-A127(T). was between 11.2 and 18.3 %. Based on the sequence similarity analyses, phenotypic, biochemical and physiological characteristics and DNA-DNA hybridization, strain L6-8(T) could be readily distinguished from its closest relatives and represents a novel species of the genus Rhizobium, for which the name Rhizobium paknamense sp. nov. is proposed. The type strain is L6-8(T) (=NBRC 109338(T)=BCC 55142(T)).