Diversity of <i>Bradyrhizobium</i> in Non-Leguminous Sorghum Plants: <i>B. ottawaense</i> Isolates Unique in Genes for N<sub>2</sub>O Reductase and Lack of the Type VI Secretion System
Sawa Wasai-Hara, Shintaro Hara, Takashi Morikawa, Masayuki Sugawara, Hideto Takami, Junich Yoneda, Tsuyoshi Tokunaga, Kiwamu Minamisawa
Abstract
Diverse members of Bradyrhizobium diazoefficiens, B. japonicum, and B. ottawaense were isolated from the roots of field-grown sorghum plants in Fukushima, and classified into “Rhizobia” with nodulated soybeans, “Free-living diazotrophs”, and “Non-diazotrophs” by nitrogen fixation and nodulation assays. Genome analyses revealed that B. ottawaense members possessed genes for N2O reduction, but lacked those for the Type VI secretion system (T6SS). T6SS is a new bacterial weapon against microbial competitors. Since T6SS-possessing B. diazoefficiens and B. japonicum have mainly been isolated from soybean nodules in Japan, T6SS-lacking B. ottawaense members may be a cryptic lineage of soybean bradyrhizobia in Japan.