Actinobacteria useful in co-contamination bioremediation process

Abstract

Mixed pollution caused by organic and inorganic compounds is a widespread problem that tends to concentrate in soils and sediments. Bioremediation technologies with microorganisms and/or plants have become the focus of interest. In the last ten years a stronger emphasis has come to be placed on the study of microbial environmentsbioremediation with heavy metals and pesticides. Actinobacteria is an important group of microorganisms by their ability to remove oil, pesticides, and heavy metals, among other substances. There have been previous studies on biotransformation of OPs or heavy metals in terms of uptake and/or reduction to less toxic forms by actinobacteria. The use of a single population involves many metabolic limitations, which could be avoided by using a mixed community. The aim of this work was to evaluate the use of actinobacteriato remediate soil co-contaminated withlindane and Cr(VI). Actinobacteria were used to remediate soil co-contaminated with Cr(VI) and lindane. Five actinobacteria, tolerant to Cr(VI) and lindane mixture were selected: Streptomyces spp. A5, A11, M7, and MC1, and Amycolatopsis tucumanensis DSM 45259. Sterilized soil samples (SSS) were inoculated with actinobacteria strains, either individually or as aconsortium, andcontaminated with Cr(VI) and lindane, either immediately or after 7 days of growth, and incubated at30 °C during 14 days.Also, inoculated SSS without toxics and non-inoculated SSS withboth toxics were used as controls.The actinobacteria showing better performance in the SSS were selected to carry out studies in non-SSS, inorder to evaluate the influence of the native microbialflora on theirability to remove Cr(VI) and lindane. This study was conducted to determine the ability ofactinobacteria to grow and remove Cr(VI) andlindane in SSS. Lindane was used at a concentration of25 mg kg-1, (2.5 times its acceptable level in soils). In control flasks, bioavailable chromiumwas reduced from 50 to12 mg kg_1 considering that a fraction of chromium wasadsorbed by soil compounds. Over time, this concentration waskept constant considering 12 mg kg-1 as 100% to furthercalculations. No variations of lindane concentrations in bothcontrol series were observed, so, there was noevidence of noticeable contribution of abiotic processes to thepesticide removal.All actinobacteria were able to grow and remove both contaminants, the consortiumformed by Streptomyces spp. A5, M7, MC1, and A. tucumanensis showed the highest Cr(VI)removal, while Streptomyces sp. M7 produced the maximum lindane removal. In non-sterile soil samples, Streptomyces sp. M7 and the consortium removed more than 40% of the lindane, while Streptomyces sp.M7 demonstrated the greatest Cr(VI) removal. The most appropriate strategy for bioremediation of Cr(VI)and lindane co-contaminated soils would be the inoculation with Streptomyces sp. M7. Streptomyces sp. M7and the consortium tested could be useful for bioremediation of soils co-contaminated with Cr(VI) and lindane. There are two strategies, either inoculation of a portion of non-sterilized soil with actinobacteria and then using this to inoculate acontaminated environment, or else using actinobacteria grown in asynthetic medium. This latter approach reduces operational time inthe laboratory and therefore reduces costs as well.