Abstract
Ochrobactrum tritici SCII24T is a highly As-resistant bacterium, with two previously described arsenic resistance operons, ars1 and ars2. Among a large number of genes, these operons contain the arsB and Acr3 genes that encode the arsenite efflux pumps responsible for arsenic resistance. Exploring the genome of O. tritici SCII24T, an additional putative operon (ars3) was identified and revealed the presence of the Acr3_2 gene that encodes for an arsenite efflux protein but which came to prove to not be required for full As resistance. The genes encoding for arsenite efflux pumps, identified in this strain, were inactivated to develop microbial accumulators of arsenic as new tools for bioremediation. Six different mutants were produced, studied and three were more useful as biotools. O. tritici wild type and the Acr3-mutants showed the highest resistance to As(III), being able to grow up to 50 mM of arsenite. On the other hand, arsB-mutants were not able to grow at concentrations higher than 1 mM As(III), and were the most As(III) sensitive mutants. In the presence of 1 mM As(III), the strain with arsB and Acr3_1 mutated showed the highest intracellular arsenic concentration (up to 17 ng(As)/mg protein), while in assays with 5 mM As(III), the single arsB-mutant was able to accumulate the highest concentration of arsenic (up to 10 ng(As)/mg protein). Therefore, arsB is the main gene responsible for arsenite resistance in O. tritici. However, both genes arsB and Acr3_1 play a crucial role in the resistance mechanism, depending on the arsenite concentration in the medium. In conclusion, at moderate arsenite concentrations, the double arsB- and Acr3_1-mutant exhibited a great ability to accumulate arsenite and can be seen as a promising bioremediation tool for environmental arsenic detoxification.
Highlights
ObjectivesThe main objective of this work was to construct an O. tritici mutant with potential for bioremediation applications, with special abilities to resist and accumulate arsenic
Arsenic is a natural metalloid widely distributed in air, water and soil, and is considered as one of the chemicals of major public health concern [1]
Annotation of the genes confirmed the presence of the arsenic resistance genes arsB and Acr3_1 already identified in this strain, included in two different chromosomally located arsenic resistance operons [11]
Summary
The main objective of this work was to construct an O. tritici mutant with potential for bioremediation applications, with special abilities to resist and accumulate arsenic. We aim to obtain an efficient bioremediation tool able to remove arsenite from the environment. The main objective of this work was to design and construct a strain with abilities to resist and accumulate arsenic in order to be used as a tool for bioremediation
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