Genome comparison of two Exiguobacterium strains from high altitude andean lakes with different arsenic resistance: identification and 3D modeling of the Acr3 efflux pump

Abstract

Arsenic exists in natural systems in a variety of chemical forms, including inorganic arsenite (As [III]) and arsenate (As [V]). The majority of living organisms have evolved various mechanisms to avoid occurrence of arsenic inside the cell due to its toxicity. Common core genes include a transcriptional repressor ArsR, an arsenate reductase ArsC, and arsenite efflux pumps ArsB and Acr3. To understand arsenic resistance we have performed arsenic tolerance studies, genomic and bioinformatic analysis of two Exiguobacterium strains, S17 and N139, from the high-altitude Andean Lakes. In these environments high concentrations of arsenic were described in the water due to a natural geochemical phenomenon, therefore, these strains represent an attractive model system for the study of environmental stress and can be readily cultivated. Our experiments show that S17 has a greater tolerance to arsenite (10 mM) than N139, but similar growth in arsenate (150 mM). We sequenced the genome of the two Exiguobacterium and identified an acr3 gene in S17 as the only difference between both species regarding known arsenic resistance genes. To further understand the Acr3 we modeled the 3D structure and identified the location of relevant residues of this protein. Our model is in agreement with previous experiments and allowed us to identify a region where a relevant cysteine lies. This Acr3 membrane efflux pump, present only in S17, may explain its increased tolerance to As(III) and is the first Acr3-family protein described in Exiguobacterium genus.

Comparative Genomics Analysis of a New Exiguobacterium Strain from Salar de Huasco Reveals a Repertoire of Stress-Related Genes and Arsenic Resistance

“…Surprisingly, strain SH31 did not show any highly relevant distinctive features. For example, previous studies found four copies of ssb in the genome of strain S17 (Ordoñez et al, 2013, 2015). In Deinococcus radiodurans , the presence of high copy numbers of ssb was proposed to be responsible for its superior radioresistance and DNA repair efficiency (Eggington et al, 2004; Cox and Battista, 2005; Norais et al, 2009).…”

High-Up: A Remote Reservoir of Microbial Extremophiles in Central Andean Wetlands

“…S17 was likewise obtained, emphasizing the fact that it contains a complete DNA repair system, including UvrABC, MutL-MutS, and bacterial photolyase, and several genes related to toxic compound resistance, such as antibiotics, arsenic, cadmium, and mercury (Ordonez et al, 2013 ). Genomic comparisons with available public genomes from Exiguobacterium suggests that one of the reasons behind high resistance to arsenic in S17 is the presence of the acr3 gene, a known contributor to cell detoxification against arsenite, one of the most toxic arsenic species (Ordoñez et al, 2015 ). All Exiguobacterium strains have a conserved arsB gene playing a role similar to acr3 , but S17 is the only one bearing both genes.…”

“…Ver3 (Albarracín et al, 2014 ), and an arsenical resistance efflux pump from Exiguobacterium sp. S17 (Ordoñez et al, 2015 ) for which medical and bioremediation applications, respectively, are envisaged. But still, much effort is required to unravel novel functions for this and other molecules that dwell in a unique biological treasure despite its being hidden high up, in the remote Andes.…”

Functional Green-Tuned Proteorhodopsin from Modern Stromatolites

“…S17. This halotolerant, UV-resistant microorganism [ 48 ] was originally isolated from modern stromatolite at L. Socompa (3,570 m; Fig 1 ) [ 41 ] being able to grow at concentrations up to 100 mM As[V] and 5mM As[III] [ 45 , 50 ]. Neighbor-Joining and maximum likelihood trees based on 16SrRNA gene sequences and MLSA of Exiguobacterium sp.…”

“…S10B and S34, yielded genes putatively encoding essential traits for survival under multiple environmental extreme conditions, e.g., high levels of UV radiation, elevated salinity, and the presence of poisoning arsenic concentrations [ 18 , 45 , 48 – 50 ]. Likewise, genes putatively coding for the bacteriorhodopsin protein family were found showing sequential features indicating the presence of proteorhodopsins and xantorhodopsins [ 18 , 45 – 47 ]. The former findings called for a more detailed, molecular investigation of the mechanisms involved in the resistance of these strains to extreme but common impairing factors in its original environment.…”