Preferential Use of the Perchlorate over the Nitrate in the Respiratory Processes Mediated by the Bacterium Azospira sp. OGA 24

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 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 (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. OGA24 in the perchlorate respiring bacteria (PRB) group was further defined by classifying it in the oryzae 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.

Microplastics in the Aquatic Environment: Occurrence, Persistence, Analysis, and Human Exposure

“…In recent years, several efforts have been devoted to the detection and removal of those contaminants that are referred to as contaminants of emerging concern (CECs), i.e., any chemical present in water or the environment at very low concentration levels, or only recently detected [1][2][3][4][5][6][7][8]. Microplastics (MP) have all the characteristics to belong to this category especially for their presence in the water environment [9].…”

Microbial Communities Associated with the Intestinal Tract of Grey Mullets from a Mediterranean Aquatic Environment

“…In this study, the most abundant bacterial family was represented by Rhodocyclaceae (47.7%) (beta-Proteobacteria) as observed by Le and Wang (2020) [30] in the gut of M. cephalus from the Taiwan Strait. Interestingly, the Rhodocyclaceae species were described by different authors for producing bioactive metabolites and, in particular, to be able to transform perchlorate into harmless chloride [50][51][52]. In this regard, Guarino 2020 [52] re-ported about the genera Azospira and Dechloromonas of Rhodocyclaceae family, able to transform perchlorate into harmless chloride, which are widely distributed in different environments such as soil and groundwater.…”

“…Interestingly, the Rhodocyclaceae species were described by different authors for producing bioactive metabolites and, in particular, to be able to transform perchlorate into harmless chloride [50][51][52]. In this regard, Guarino 2020 [52] re-ported about the genera Azospira and Dechloromonas of Rhodocyclaceae family, able to transform perchlorate into harmless chloride, which are widely distributed in different environments such as soil and groundwater. Nowadays, perchlorate (ClO4-) is an ubiqui-tous ion released into the environment by anthropogenic activity although significant quantities of perchlorate are naturally formed in the atmosphere, especially during thun-derstorms [51,53,54].…”

Isolation and identification of chlorate-reducing Hafnia sp. from milk

“…Microbial reduction of chlorine oxyanions under anaerobic conditions has been documented for over 70 years [17][18][19][20][21][22][23], though there is sparse information on the microbes that are capable of this metabolic conversion or on the biochemical pathways. Biologically mediated (per)chlorate reduction has been noted to occur in a wide range of environments and is associated with a class of micro-organisms called dissimilatory (per)chlorate-reducing bacteria (DPRBs), with many strains isolated and characterized in recent years contributing to a greater understanding of this phenomenon [17,21,[24][25][26][27][28]. This reduction by DPRBs produces harmless chloride ions and has created much interest as a potential means of remediating (per)chlorate contamination in the environment [29].…”