Species of associative N2-fixing bacteria in phytophysiognomies of the Quadrilátero ferrífero, MG, Brazil

Abstract

Mining is essential for the socioeconomic development of a country; however, it generates severe environmental impacts and negative effects on edaphic biodiversity. Many methods are used for the rehabilitation of degraded areas; especially revegetation with native species. This method can be enhanced if combined with inoculation with plant growth-promoting microorganisms. Thus, surveys and studies of the diversity of these microorganisms, such as associative N2-fixing bacteria, are the first step for their subsequent use in rehabilitation of degraded areas. The objective of this study was to isolate, characterize, and identify associative N2-fixing bacteria in dry and rainy seasons in soil samples from four phytophysiognomies in the Quadrilátero Ferrífero (“Iron Quadrangle” mining region): Atlantic Forest, Cerrado (neotropical savanna), Canga (ironstone outcrops), and an area revegetated with grasses after iron mining. The isolates were obtained by using NFb and FAM as culture media. After culture characterization, partial sequencing of the 16S rDNA gene was carried out for comparison with sequences available in GenBank. A total of 37 strains were obtained from all the phytophysiognomies examined, except for Atlantic Forest. The culture media allowed growth typical of diverse N2-fixing bacteria. Gluconacetobacter diazotrophicus, usually considered obligate endophytic, was the species of highest frequency among the strains isolated from soil. Higher density and diversity were found in the grass phytophysiognomy, suggesting the effectiveness of the rehabilitation processes regarding N2-fixing bacteria.