Phylogenomic analysis of Rhizobiaceae strains from the Cerrado biome, Brazil, reveals a novel genus, Brasilibacterium gen. nov., and three novel species: Brasilibacterium cachoeirinhense sp. nov., Brasilibacterium lagoinhense sp. nov., and Martinezella lalimensis sp. nov.

Rhizobiaceae is one of the most representative families, encompassing rhizobial species, valuable allies in the sustainable production of legumes such as cowpea (Vigna unguiculata). Interestingly, beyond rhizobia, studies have increasingly reported the presence of a wide diversity of non-symbiotic bacteria that compose the microbiome of cowpea nodules. In this study, we performed a systematic analysis, with an emphasis on phylogenomic aspects, of 12 strains trapped from cowpea in soils of indigenous lands in Mato Grosso do Sul, Central-Western Brazil (Cerrado biome), which had been preliminarily characterized. The results highlighted the rich and little-explored Rhizobiaceae biodiversity, revealing a novel genus, Brasilibacterium gen. nov., and three novel species: Brasilibacterium cachoeirinhense sp. nov. (CNPSo 3794T = BR 15710T = LMG 34800T), Brasilibacterium lagoinhense sp. nov. (CNPSo 3920T = BR 15708T = 34801T), and Martinezella lalimensis sp. nov. (CNPSo 3959T = BR 15709T = LMG 34802T). However, none of the strains belonging to these novel species was able to re-nodulate cowpea or the promiscuous legumes Phaseolus vulgaris and Macroptilium atropurpureum, suggesting either the loss of symbiotic genes or their endophytic nature. In addition to the novel species accessed, "Rhizobium atlanticum", "Martinezella aureum", "Martinezella centroccidentale", "Martinezella hainanensis", and "Martinezella dioscoreae" were also identified based on genomic sequences, with the latter two reported for the first time in Brazil.