Preferential Use of the Perchlorate over the Nitrate in the Respiratory Processes Mediated by the Bacterium <i>Azospira</i> sp. OGA24

• Main Authors: Francesco Guarino, Oriana Motta, Mimmo Turano, Antonio Proto, Giovanni Vigliotta
• Format: Article
• Language: English
• Published: MDPI AG 2020-08-01
• Series: Water
• Subjects: perchlorate respiring bacteria (PRB); strain <i>Azospira</i> sp. OGA24; emerging pollutants; bioremediation; reverse transcriptase-polymerase (RT-PCR); periplasmic and membrane nitrate reductase
• Online Access: https://www.mdpi.com/2073-4441/12/8/2220

Here we report the results obtained for a strain isolated from a polluted site and classified as <i>Azospira</i> sp. OGA 24. The capability of OGA24 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 (<i>pcr</i>A), chlorite dismutase (<i>cld</i>), and periplasmic nitrate reductase large subunit (<i>nap</i>A). 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, <i>nap</i>A was completely inhibited in the presence of perchlorate as the only electron acceptor, <i>pcr</i>A 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 <i>Azospira</i> sp. OGA24 in the perchlorate respiring bacteria (PRB) group was further defined by classifying it in the <i>oryzae</i> species. The respiratory characteristics of OGA24 strain make it very attractive in terms of potential applications in the bioremediation of environments exposed to perchlorate salts.