Identification of Resistance Genes and Response to Arsenic in Rhodococcus aetherivorans BCP1

Abstract

Arsenic (As) ranks among the priority metal(loid)s that are of public health concern. In the environment, arsenic is present in different forms, organic or inorganic, featured by various toxicity levels. Bacteria have developed different strategies to deal with this toxicity involving different resistance genetic determinants. Bacterial strains of Rhodococcus genus, and more in general Actinobacteria phylum, have the ability to cope with high concentrations of toxic metalloids, although little is known on the molecular and genetic bases of these metabolic features. Here we show that Rhodococcus aetherivorans BCP1, an extremophilic actinobacterial strain able to tolerate high concentrations of organic solvents and toxic metalloids, can grow in the presence of high concentrations of As(V) (up to 240 mM) under aerobic growth conditions using glucose as sole carbon and energy source. Notably, BCP1 cells improved their growth performance as well as their capacity of reducing As(V) into As(III) when the concentration of As(V) is within 30–100 mM As(V). Genomic analysis of BCP1 compared to other actinobacterial strains revealed the presence of three gene clusters responsible for organic and inorganic arsenic resistance. In particular, two adjacent and divergently oriented ars gene clusters include three arsenate reductase genes ( arsC 1/2/3) involved in resistance mechanisms against As(V). A sequence similarity network (SSN) and phylogenetic analysis of these arsenate reductase genes indicated that two of them (ArsC2/3) are functionally related to thioredoxin (Trx)/thioredoxin reductase (TrxR)-dependent class and one of them (ArsC1) to the mycothiol (MSH)/mycoredoxin (Mrx)-dependent class. A targeted transcriptomic analysis performed by RT-qPCR indicated that the arsenate reductase genes as well as other genes included in the ars gene cluster (possible regulator gene, arsR , and arsenite extrusion genes, arsA, acr3 , and arsD ) are transcriptionally induced when BCP1 cells were exposed to As(V) supplied at two different sub-lethal concentrations. This work provides for the first time insights into the arsenic resistance mechanisms of a Rhodococcus strain, revealing some of the unique metabolic requirements for the environmental persistence of this bacterial genus and its possible use in bioremediation procedures of toxic metal contaminated sites.

Biotechnology of Rhodococcus for the production of valuable compounds

“…Another distinctive case is represented by BCP1 incubated with increasing concentrations of arsenate [AsO 4 3- , also referred to as As(V)] in the presence of glucose as the sole carbon and energy source. Here, some preliminary TEM analyses showed the presence of electron-dense hexagonal nanoplates (possibly associated to metal(loid) biosorption) that deserve further analysis (Firrincieli et al 2019 ).

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“…Further, several Rhodococcus spp. strains have recently been described to be able to produce metal-based nanostructures as the result of metal and metalloid [metal(loid)] bioconversion into their elemental state (Presentato et al 2016(Presentato et al , 2018a(Presentato et al , 2018bFirrincieli et al 2019).…”

Co‐occurrence of antibiotic, biocide, and heavy metal resistance genes in bacteria from metal and radionuclide contaminated soils at the Savannah River Site

“…The zinc resistance gene zraR / hydH was the most abundant MRG subtype, and this along with copper resistance genes have been reported in the literature as being strong contributors to resistance traits, having direct correlations with as β‐lactamases, sulphonamides, macrolide‐lincosamide‐streptogramin and tetracycline resistance genes (Knapp et al , 2017). Arsenic associated resistance genes such as those in the ars gene clusters have been shown to be globally distributed and are suggested to have prominent roles in global arsenic biogeochemistry (Ben Fekih et al , 2018; Dunivin et al , 2019; Firrincieli et al , 2019). Iron and nickel resistance genes have also been shown to be significantly associated with ARGs such as multidrug, β‐lactamases, sulphonamides, macrolide‐lincosamide‐streptogramin, tetracycline, aminoglycosides and vancomycin resistance genes (Guo et al , 2014; Hu et al , 2017).…”

Microbial interaction with and tolerance of radionuclides: underlying mechanisms and biotechnological applications

“…Transcriptomics is acquiring a crucial role in bioremediation studies through the analysis of gene expression and regulation. For instance, a targeted gene expression analysis indicated the transcriptional induction of arsenate reductase genes, among others related to the ars gene cluster (arsR, arsA, acr3 and arsS) by the cells of Rhodococcus aetherivorans BCP1 when grown in the presence of As(V) at sublethal concentrations (Firrincieli et al, 2019). The latter work revealed that unique metabolic mechanisms of a Rhodococcus strain could tolerate this toxic metal.…”