| Congresso Brasileiro de Microbiologia 2023 | Resumo: 190-1 | ||||
Resumo:Bradyrhizobium is known for its ability to fix atmospheric nitrogen in symbiosis with agronomically important crops like soybean. This study focused on a group of eight natural variants of B. japonicum strain SEMIA 566 and other group containing eight variants of B. diazoefficiens strain SEMIA 586, used in commercial inoculants for soybean in Brazil in the 1960s and 1970s. Nowadays, the main commercial strains are B. japonicum CPAC 15 (=SEMIA 5079) and B. diazoefficiens CPAC 7 (=SEMIA 5080), which are variants of SEMIA 566 and SEMIA 586, respectively. CPAC 15 is very competitive for nodule occupation, whereas CPAC 7 is very effective in fixing nitrogen. Concerning the other variant strains of this study, six were more competitive than CPAC 15, whereas two showed higher nitrogen fixation capacity than CPAC 7. The main goal of the study was to detect how genetic variations in the strains impacts these phenotypes. The approach included the phylogenetic analysis of the core genome in each species group, calculation of the average nucleotide identity (ANI), and analysis of the pangenome to identify loss or gain of genes and occurrence of single nucleotide polymorphisms (SNPs) in the symbiotic islands. All strains were phylogenetically closely related within each group, with ANI values above 99.91%. Interestingly, five variant strains of the CPAC 15 group presented two plasmids each, an unusual characteristic of Bradyrhizobium. Although the strains containing plasmids carried one extra set of genes of the type III (T3SS) and two of the type IV (T4SS) secretion systems that might affect symbiosis, there was no correlation with the competitiveness phenotype. The B. japonicum group presented a larger pangenome with 10,550 genes and 1,151 SNPs, whereas the B. diazoefficiens group presented 8,665 genes and 57 SNPs. The greater variability in the B. japonicum group is probably consequence of its longer adaptation time to the Cerrados soil. Unique SNPs in genes of the B. japonicum group could be related to higher competitiveness in some variant strains, such as the virD2 encoding a component of T4SS, nopE, that encodes for an effector protein of the T3SS, a PAS domain S-box encoding a protein related to cell regulatory functions, and a bacA-like gene related to bacteroid differentiation in symbiosis. The other SNPs found in this group were related to general metabolism and may indirectly affect the strain competitiveness. No unique SNPs were found in strains of the B. diazoefficiens group. Overall, 54 to 57% of the pangenomes are composed by genes encoding hypothetical proteins that might be involved in different strain phenotypes. In conclusion, genetic diversity was detected in both Bradyrhizobium groups, with several SNPs and genes encoding hypothetical proteins that need to be evaluated to find their roles in different strain phenotypes. Palavras-chave: genomics, bioinformatics, rhizobia, nitrogen fixation, inoculants Agência de fomento:INCT - Plant Growth-Promoting Microorganisms for Agricultural Sustainability and Environmental Responsibility (CNPq 465133/2014-4, Fundação Araucária-STI 043/2019, CAPES). | |||||