Sorghum Growth Promotion by Paraburkholderia tropica and Herbaspirillum frisingense: Putative Mechanisms Revealed by Genomics and Metagenomics

Abstract

Bacteria from the genera Paraburkholderia and Herbaspirillum can promote the growth of Sorghum bicolor, but the underlying mechanisms are not yet known. In a pot experiment, sorghum plants grown on sterilized substrate were inoculated with Paraburkholderia tropica strain IAC/BECa 135 and Herbaspirillum frisingense strain IAC/BECa 152 under phosphate-deficient conditions. These strains significantly increased Sorghum bicolor cultivar SRN-39 root and shoot biomass. Shotgun metagenomic analysis of the rhizosphere revealed successful colonization by both strains; however, the incidence of colonization was higher in plants inoculated with P. tropica strain IAC/BECa 135 than in those inoculated with H. frisingense strain IAC/BECa 152. Conversely, plants inoculated with H. frisingense strain IAC/BECa 152 showed the highest increase in biomass. Genomic analysis of the two inoculants implied a high degree of rhizosphere fitness of P. tropica strain IAC/BECa 135 through environmental signal processing, biofilm formation, and nutrient acquisition. Both genomes contained genes related to plant growth-promoting bacterial (PGPB) traits, including genes related to indole-3-acetate (IAA) synthesis, nitrogen fixation, nodulation, siderophore production, and phosphate solubilization, although the P. tropica strain IAC/BECa 135 genome contained a slightly more extensive repertoire. This study provides evidence that complementary mechanisms of growth promotion in Sorghum might occur, i.e., that P. tropica strain IAC/BECa 135 acts in the rhizosphere and increases the availability of nutrients, while H. frisingense strain IAC/BECa 152 influences plant hormone signaling. While the functional and taxonomic profiles of the rhizobiomes were similar in all treatments, significant differences in plant biomass were observed, indicating that the rhizobiome and the endophytic microbial community may play equally important roles in the complicated plant-microbial interplay underlying increased host plant growth.

Metabolic Footprints of Burkholderia Sensu Lato Rhizosphere Bacteria Active against Maize Fusarium Pathogens

“…These were unevenly distributed among the different groups, as shown by (1) the detection of clade II B. gladioli 1Ma4 as a lone IAA hyper-accumulator; (2) the dispersal of PS and nitrogen-fixing strains in clades I and III and (3) the dominance of EPS production in the clade I strains. The detection of IAA and N-fixing activity in Bcc strains belonging to clade I and in the two others was in accordance with the studies by Suárez-Moreno et al [26], Caballero-Mellado et al [72], Angus et al [73], Martínez-Aguilar et al [76] and Estrada de los Santos et al [77], while PS and EPS production by Bcc and Paraburkholderia bacteria similar to those grouped in clades I and III, respectively, was associated with the growth promotion of C4 plants [77][78][79][80][81]. These results strongly suggest that these Burkholderia strains could be important maize plant growth-promoting bacteria.…”

Sweet Sorghum Genotypes Tolerant and Sensitive to Nitrogen Stress Select Distinct Root Endosphere and Rhizosphere Bacterial Communities

“…However, some plant beneficial bacteria were enriched in the sensitive lines under high-N, such as Pseudomonadaceae and Rhodocyclaceae in the root endosphere [ 71 , 72 , 73 , 74 ], and Enterobacteriaceae in the rhizosphere [ 75 , 76 , 77 , 78 , 79 ]. Interestingly, the endophytic N-fixing genera Herbaspirillum and Azospirillum were enriched in the root endosphere of the sensitive lines under high-N and low-N conditions, respectively [ 80 , 81 , 82 ]. These results are surprising because they suggest that N-stress sensitive lines host diazotrophic bacteria in root tissues which could compensate for the higher susceptibility to N starvation, while N-stress tolerant genotypes harbor bacteria able to alleviate the abiotic stress — which may be more effective.…”

Plant-Growth Endophytic Bacteria Improve Nutrient Use Efficiency and Modulate Foliar N-Metabolites in Sugarcane Seedling

“…All six strains obtained from Agronomic Institute (IAC, Campinas, Brazil) Culture Collection were isolated from the root endosphere of healthy sugarcane plants (Saccharum officinarum L.). These strains were previously characterized for plant growth traits such as antagonistic activities against phytopathogens, indole-3-acetic acid (IAA) production, PCR amplification of the nifH gene, and phosphate solubilization, besides improving sugarcane plant growth in previous researches [6,13,[18][19][20], as summarized in Table 1. The bacterial strains were grown in DYGS medium for 72 h at 28 • C. Each inoculum was centrifuged (12,000 rpm, 10 min), suspended in a sterile solution of 0.01 mol•L −1 MgSO 4 •7H 2 O and adjusted to a density of 10 8 colony forming units (CFU)•mL −1 .…”