Bioprospection of Bacterial Strains from Chromite Process Industry Residues from Mexico for Potential Remediation

Industrial residues with high concentrations of hexavalent chromium [Cr(VI)], characterized by an alkaline pH (between 9 and 13) and high salinity (around 100 psu), were used as a source for extremophilic chromium-resistant and -reducing microorganisms. An investigation of biodiversity through MiSeq showed the presence of 20 bacterial classes, with <i>Bacilli</i> (47%), <i>Negativicutes</i> (15%), <i>Bacteriodia</i> (8%), <i>Gammaproteobacteria</i> (7%) and <i>Clostridia</i> (5%) being the most abundant. The bioprospection allowed the cultivation of 87 heterotrophic bacterial colonies and 17 bacterial isolates at the end of the isolation, and screening procedures were obtained. The isolates were related to <i>Cellulosimicrobium aquatile</i>, <i>C. funkei</i>, <i>Acinetobacter radioresistens</i>, <i>Staphylococcus equorum</i>, <i>S. epidermis</i>, <i>Brachybacterium paraconglometratum</i>, <i>Glutamicibacter creatinolyticus</i>, <i>Pseudomonas songnenensis</i>, <i>Microbacterium algeriense</i> and <i>Pantoea eucalypti</i>, most of them being resistant to Cr(VI). Resistances of up to 400 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mi mathvariant="normal">m</mi><mi mathvariant="normal">g</mi><mo>.</mo><mi mathvariant="normal">L</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula> of chromate were obtained for four related strains (QReMLB55A, QRePRA55, QReMLB33A and QReMLB44C). The <i>C. aquatile</i> strain QReMLB55A and the <i>P. songnenensis</i> strain QReMLB33A were exposed to <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msub><mrow><mi mathvariant="normal">K</mi></mrow><mrow><mn>2</mn></mrow></msub><msub><mrow><mi mathvariant="normal">C</mi><mi mathvariant="normal">r</mi></mrow><mrow><mn>2</mn></mrow></msub><msub><mrow><mi mathvariant="normal">O</mi></mrow><mrow><mn>7</mn></mrow></msub></mrow></semantics></math></inline-formula> (200 <inline-formula><math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><semantics><mrow><msup><mrow><mi mathvariant="normal">m</mi><mi mathvariant="normal">g</mi><mo>.</mo><mi mathvariant="normal">L</mi></mrow><mrow><mo>−</mo><mn>1</mn></mrow></msup></mrow></semantics></math></inline-formula>) under optimal conditions, diminishing 94% and 24% of the Cr(VI) in 6 days, respectively. These strains exhibited a high potential for chromium remediation biotechnologies.