Soil Chromium Bioremediation: Enhanced Activity of Actinobacteria with Plants

Abstract

Chromium is widely distributed in nature. Due to its use, chromium contamination in soils and groundwater has been detected in a variety of industrial sites. Cr(VI) causes acute and chronic toxicity, and is 1,000 times more toxic and mutagenic than Cr(III). Bioremediation may then be an alternative to remove environmental pollutants. Actinobacteria constitute the largest number of microbial populations found in soil and have a high potential for use in bioremediation processes. On the other hand, contamination levels in plant samples can be used as indicators of the same, since plants can adsorb/absorb toxic substances from soil through their roots. The aim of this work was to evaluated a strategy to bioremediate Cr(VI) using Streptomyces sp. MC1 and maize plants. Soil samples were contaminated with 100, 200 and 400 mg kg-1 of Cr(VI) or Cr(III) and bioavailable chromium levels were measured. Bioavailable chromium (35%) was only detected in samples contaminated with Cr(VI).In soil samples with Cr(VI) 200 mg kg-1inoculated with Streptomyces sp. MC1, a decrease up to 73% bioavailable Cr was found, after 42 days of incubation,. Zea mays seedlings were planted in soil samples with Cr(VI) or Cr(III). Plantlets accumulated chromium in roots, stems and leaves, mainly as Cr(III), also biomass decreased up to 88%. Streptomyces sp. MC1 was inoculated in soil samples with 200 mg kg-1 of Cr(VI) and Zea mays seedlings were planted of at the time of inoculation, 14 or 28 days after contamination/inoculation. Streptomyces sp. MC1 caused increase of Zea mays biomass, from 56 to 88 mg when the seedlings were planted 28 days after the contamination with Cr(VI). Chromium accumulation decreased up to 46% in Zea mays, compared with non-inoculated samples. When seedlings were planted 28 days after inoculation with Streptomyces sp. MC1, bioavailable chromium reduction was 96%. We report, for the first time, a cooperative action between actinobacteria and Zea mays in bioremediation processes.