Cross-feeding entre actinobactérias e rizóbios do Semiárido nordestino e seu papel na prospecção de novos biofertilizantes

Abstract

Found in soils, animal excreta, algae, lichens, plants, oceans and even extreme environments, actinobacteria are Gram-positive filamentous microorganisms known to produce various secondary metabolites. Their ability to synthesize antibiotics, immunosuppressants, antivirals and exoenzymes such as cellulase, amylase and xylanase gives them great biotechnological potential. Also found in soil, rhizobia are bacteria that are equally important economically and ecologically. Responsible for transforming atmospheric nitrogen into ammonia, they are mainly present in symbiosis in legume root nodules. The unfavorable conditions faced by plants in the semiarid soil make them dependent on the microorganisms present in their rhizosphere, which are capable of optimizing the biological activity of the soil, facilitating plant growth. The aim of this work was to co-inoculate strains from two bacterial phyla isolated from soils from the Brazilian Northeastern semi-arid region in order to study the potential of actinobacteria to facilitate rhizobia growth. From the culture collection of the Laboratory of Environmental Microbiology (LAMAB) of the Federal University of Ceará, 10 strains of actinobacteria with cellulolytic, amylolytic and xylanolytic activity statistically different from the others and 7 strains of rhizobia genetically identified at the species level and without the aforementioned enzymatic activities were selected. A characterization of the macromorphology and micromorphology of actinobacteria was carried out, observing their structures via optical and electron microscopy. Co-inoculation of microorganisms was performed in culture media containing starch, xylan and carboxymethylcellulose (CMC) as the sole carbon sources, from which rhizobia growth was evaluated. Of a total of 70 pairs of actinobacteria and rhizobia, 45 were positive in the medium with CMC, 47 in the medium with xylan and 9 in the medium with starch. Thus, it is concluded that exoenzymes synthesized by actinobacteria hydrolyze substrates into simpler sugars, allowing that even if the used diazotrophic bacteria are unable to metabolize complex substrates, they are able to grow in these culture media. This interaction is promising for the development of a new bioinoculant based on the co-inoculation of these two rhizobacteria that promote plant growth.