Streptomyces Growth Capacity in the Presence of Boron

Abstract

Boron (B) environmental pollution in Salta, Argentina, is mainly due to aggressive mining exploitation and boron compound processing, which provide great revenue profits to the state. One likely system to solve soil B contamination increasingly under study is that of bioremediation through bacteria able to grow and eliminate B or its derivatives. Few species are mentioned in literature. Other researchers isolated some bacteria from naturally boron contaminated soils in Hisarcik, Turkey, requiring B to grow or to hold high B concentrations or even accumulate high boronic acid concentrations inside, but so far no conclusive results have been published as to the genus of Streptomyces. In former researches, the study area was determined, soil sampling was conducted and microorganisms were isolated from an anthropic zone (Baradero) and from a naturally contaminated area (Tincalayu) in Salta state, Argentina. Out of the 127 microorganisms initially isolated, 50 were identified according to the colony morphologic features applying different staining and chemical taxonomic tests using API 20 NE (Biomerieux). Out of 17 Gram positive isolates, eight belong to the actinobacteria group, according to molecular identification by 16S ADNr. Boric acid qualitative and quantitative tolerance studies were continued with the eight strains selected on the basis of their abundance in the soils under study, their metabolic versatility and mainly, non-pathogenic. These strains selected from boron contaminated soils were sequenced and identified at molecular level and their sequences were added to the GenBank. Their growth has been studied in minimal liquid medium with different boric acid concentrations (20, 40 and 80 mM). The results varied with the strains, i.e. increasing boric concentration affected negatively the growth of Streptomyces Iakyrus, while that effect was not observed for S. achromogenes which instead did produce an exopolisaccharide.