Diversity and functionality of rhizobacteria associated with different growth stages of maize plants under field conditions
Abstract
The near root region of plants (rhizosphere) is a complex terrain where bacteria communities play significant roles in ecological system functions. The rhizosphere is capable of both directly and indirectly influencing the composition, diversity, and productivity of plant communities, thus, the belowground community has been suggested as an indicator of aboveground plant health and productivity. As a consequence, deeper knowledge underlying the dynamics and determinants of soil bacteria communities is critical for the comprehension of processes influencing or impacting soil fertility and agricultural sustainability. In our study, we used the new oxford nanopore sequencing technology (MinION) to analyze raw DNA samples recovered from the rhizospheric soil of maize plants at two growth stages (flowering and senescence) and bulk soil of the North-West University, Agricultural farmland, Mmabatho, Mafikeng, South Africa, and comparatively analyzed the functional diversities of both the rhizospheric soil and bulk soil of the bacteria communities. We hypothesized that bacteria communities around the root of maize are impacted by both growth stages and physicochemical properties of the soil. Our study revealed significant differences in taxonomic structures at the different growth stages and that taxonomic distributions were predominantly impacted by selected physicochemical parameters during the flowering stages. The predominating influential elements of soil properties (i.e pH, N, P, K) and precise shift of particular taxa provide insights into the agricultural practices. Therfore, it could be inferred that fertilization and agronomical practices cause changes in these elements and impact bacterial diversity. Cultural techniques may underestimate bacteria diversity but metagenomics, using whole-genome sequencing allows the estimation of the bacterial community more explicitly as well as the characterization of functions altogether. Our study revealed a distinctive selection at both taxonomic and functional profiles operating in
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the assemblage of the maize rhizosphere community. Of the over 2 million reads, the result showed that Proteobacteria and Firmicutes were most prevalent (>40%). At the genus level, dominant rhizosphere genera (Chlorasidobacterium, Candidatus, Flavisoli bacter Gaiella, Bacillus, Pseudomonas, Flavobacterium, etc.) displayed different patterns of temporal changes in the rhizosphere as opposed to the bulk soil. Moreover, we observed unique genera, in particular, Plant-Growth Promoting Rhizobacteria (PGPR) such as Bacillus, Pseudomonas, Psychrobacter, Nonomuraea, Thiobacillus and Bradyrhizobium etc. Regarding functional profiles, data obtained showed significant differences in subsystems such as nitrogen fixation, carbohydrates metabolism, and metabolism of aromatic compounds. possible reason being high organic substances in the root region and increased prevalence of certain genera with high pesticide degradability, sequences of the adenylate cyclase (cAMP) pathway, which confer stability on bacteria community, among others. On the other hand, bulk soil had more sequences relating to dormancy and motility, sporulation, and stress response when compared with bulk soil. Nevertheless, the diversity and abundance of the taxa viewed does not correspond with functional traits identified, which could indicate some level of bacterial redundancy. Our study broadens our understanding of the assemblage, composition and function of the maize rhizosphere bacteria community in general, and has express implications in agricultural sustainability.