Abstract
Here we report the results obtained for a strain isolated from a polluted site and classified as Azospira sp. OGA 24. The capability of OGA 24 to utilize perchlorate and nitrate and the regulation of pathways were investigated by growth kinetic studies and analysis of messenger RNA (mRNA) expression of the genes of perchlorate reductase alpha subunit (pcrA), chlorite dismutase (cld), and periplasmic nitrate reductase large subunit (napA). In aerobic conditions and in a minimal medium containing 10 mM acetate as carbon source, 5.6 ± 0.34 mmol L−1 perchlorate or 9.7 ± 0.22 mmol L−1 nitrate were efficiently reduced during the growth with 10 mM of either perchlorate or nitrate. In anaerobiosis, napA was completely inhibited in the presence of perchlorate as the only electron acceptor, pcrA was barely detectable in nitrate-reducing conditions. The cell growth kinetics were in accordance with expression data, indicating a separation of nitrate and perchlorate respiration pathways. In the presence of both compounds, anaerobic nitrate consumption was reduced to 50% (4.9 ± 0.4 vs. 9.8 ± 0.15 mmol L−1 without perchlorate), while that of perchlorate was not affected (7.2 ± 0.5 vs. 6.9 ± 0.6 mmol L−1 without nitrate). Expression analysis confirmed the negative effect of perchlorate on nitrate respiration. Based on sequence analysis of the considered genes and 16S ribosomal gene (rDNA), the taxonomic position of Azospira sp. OGA 24 in the perchlorate respiring bacteria (PRB) group was further defined by classifying it in the oryzae species. The respiratory characteristics of OGA 24 strain make it very attractive in terms of potential applications in the bioremediation of environments exposed to perchlorate salts.
Highlights
Perchlorate (ClO4 − ) is a ubiquitous ion released into the environment by anthropogenic and natural sources
The capability of OGA 24 strain to use perchlorate was tested by kinetic studies in batch experiments
OGA 24 was pre-grown aerobically in VG minimal medium containing acetate as carbon source and electron donor, and it was inoculated, at exponential phase in anaerobic conditions, in the fresh medium supplemented with 10 mM acetate and 10 mM perchlorate as the only electron acceptor
Summary
Perchlorate (ClO4 − ) is a ubiquitous ion released into the environment by anthropogenic and natural sources. Military and commercial applications of perchlorate salts as oxidizers in propellants, flares, munitions, matches, fireworks, blasting agents are the main anthropogenic perchlorate sources, while the natural ones are the nitrate salts from Chilean deposits, phosphorus-bearing minerals founded in arid locations, potash ore from New Mexico and Canada [1]. Water 2020, 12, 2220 contaminant in water, beverages, fresh produce, and other sources of human exposure all over the world [4], and its toxicity raises public health concerns. The main effect on human beings is its action on the thyroid gland by inhibiting iodide uptake and synthesis of thyroid-stimulating hormone, with serious impairments of growth, metabolism, and reproduction [5,6,7,8].
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