Three novel diazotrophic species, Paenibacillus oryziterrae sp. nov., Paenibacillus paludis sp. nov. and Paenibacillus diazotrophicus sp. nov., isolated from red paddy soil with potential for consortium-based rice growth promotion

Biological nitrogen fixation is central to sustainable rice cultivation, yet diazotrophicPaenibacillusspecies from red paddy soils remain poorly characterized. Here, three novelPaenibacillusstrains, sgz500958T, sgz500992Tand sgz5001063T, were isolated from red paddy soils in China. Phylogenetic and phylogenomic analyses based on 16S rRNA and whole-genome data revealed that the three strains formed distinct lineages withinPaenibacillus, with average nucleotide identity values below 95% relative to their closest reference strains. All strains possessed a completenifgene cluster and exhibited nitrogenase activity, and strain sgz5001063Tmaintained high activity at low concentrations (0–3 mM), was inhibited at intermediate concentrations (4–30 mM) and recovered at very high ammonium concentrations (30–300 mM). Utilizing complementary plant growth-promoting traits and co-culture compatibility, two nitrogen-fixing synthetic communities (NFSCs) were assembled. In rice assays, NFSC2 markedly enhanced germination (100%), shoot height (+72.5%) and root growth relative to sgz5001063Talone and NFSC1. The isolates are proposed asPaenibacillus oryziterraesp. nov. (sgz500958T=MCCC 1K09377T=KCTC 43740T),Paenibacillus paludissp. nov. (sgz500992T=MCCC 1K09376T=KCTC 43729T) andPaenibacillus diazotrophicussp. nov. (sgz5001063T=MCCC 1K09391T=KCTC 43741T).