Diversity of heterotrophic aerobic cultivable microbial communities of soils treated with fumigants and dynamics of metabolic, microbial, and mineralization quotients

A combination of molecular and classical techniques was used to study the composition, structure, diversity, and dynamics of an aerobic heterotrophic cultivable bacterial community isolated from five different soil samples treated with the fumigant agent 1,3-dichloropropene (1,3-D) and further subjected to nitrogen-phosphorous-potassium (NPK) fertigation (F), amendment (C-2 and C-4), and NPK fertigation plus amendment (F+C) in two different periods (May and July). The restriction and sequence analysis of 16S rDNA from 189 isolates revealed a very high percentage (94%) of Gram-positive bacterial isolates, most of which (83%) belonging to the genus Bacillus. The degree of intraspecific genetic diversity was high, as shown by random amplified polymorphic DNA analysis. These data seem to be related with the increase in microbial biomass C (C-mic) content and the decrease in the total organic C (C-org) and metabolic quotient (qCO(2)) values, especially in amended soils (C-2, C-4) where soil microflora mineralized the organic matter of the added fertilizers. In a short term, it is suggested that the presence of very high percentage of Gram-positive bacteria might be related to the ability of these bacteria to form spores so as to be resistant to fumigants rather than being the result of a selective pressure in the predominance of microbial species with a set of genes involved in biodegradation of 1,3-D.