Fusibacter sp. 3D3 (ATCC BAA-2418) is an arsenate-reducing halotolerant strain within the Firmicutes phylum, isolated from the Salar de Ascotán, a hypersaline salt flat in Northern Chile. This high-Andean closed basin is an athalassohaline environment located at the bottom of a tectonic basin surrounded by mountain range, including some active volcanoes. This landscape can be an advantageous system to explore the effect of salinity on microorganisms that mediate biogeochemical reactions. Since 2000, microbial reduction of arsenic has been evidenced in the system, and the phylogenetic analysis of the original community plus the culture enrichments has revealed the predominance of Firmicutes phylum. Here, we describe the first whole draft genome sequence of an arsenic-reducing strain belonging to the Fusibacter genus showing the highest 16S rRNA gene sequence similarity (98%) with Fusibacter sp. strain Vns02. The draft genome consists of 57 contigs with 5,111,250 bp and an average G + C content of 37.6%. Out of 4780 total genes predicted, 4700 genes code for proteins and 80 genes for RNAs. Insights from the genome sequence and some microbiological features of the strain 3D3 are available under Bioproject accession PRJDB4973 and Biosample SAMD00055724. The release of the genome sequence of this strain could contribute to the understanding of the arsenic biogeochemistry in extreme environments.Electronic supplementary materialThe online version of this article (doi:10.1186/s40793-017-0252-4) contains supplementary material, which is available to authorized users.

Eight nucleotide sequences containing a single rhodanese domain were found in the Acidithiobacillus ferrooxidans ATCC 23270 genome: p11, p14, p14.3, p15, p16, p16.2, p21, and p28. Amino acids sequence comparisons allowed us to identify the potentially catalytic Cys residues and other highly conserved rhodanese family features in all eight proteins. The genomic contexts of some of the rhodanese-like genes and the determination of their expression at the mRNA level by using macroarrays suggested their implication in sulfur oxidation and metabolism, formation of Fe-S clusters or detoxification mechanisms. Several of the putative rhodanese genes were successfully isolated, cloned and overexpressed in E. coli and their thiosulfate:cyanide sulfurtransferase (TST) and 3-mercaptopyruvate/cyanide sulfurtransferase (MST) activities were determined. Based on their sulfurtransferase activities and on structural comparisons of catalytic sites and electrostatic potentials between homology- modeled A. ferrooxidans rhodaneses and the reported crystal structures of E. coli GlpE (TST) and SseA (MST) proteins, two of the rhodanese-like proteins (P15 and P16.2) could clearly be defined as TSTs, and P14 and P16 could possibly correspond to MSTs. Nevertheless, several of the eight A. ferrooxidans rhodanese-like proteins may have some different functional activities yet to be discovered.

SummaryThe bioleaching of metal sulfide has developed into a very important industrial process and understanding the microbial dynamic is key to advancing commercial bioleaching operations. Here we report the first quantitative description of the dynamic of active communities in an industrial bioleaching heap. Acidithiobacillus ferrooxidans was the most abundant during the first part of the leaching cycle, while the abundance of Leptospirillum ferriphilum and Ferroplasma acidiphilum increased with age of the heap. Acidithiobacillus thiooxidans kept constant throughout the leaching cycle, and Firmicutes group showed a low and a patchy distribution in the heap. The Acidiphilium‐like bacteria reached their highest abundance corresponding to the amount of autotrophs. The active microorganisms in the leaching system were determined using two RNA‐based sensitive techniques. In most cases, the 16S rRNA copy numbers of At. ferrooxidans, L. ferriphilum, At. thiooxidans and F. acidiphilum, was concomitant with the DNA copy numbers, whereas Acidiphilium‐like bacteria and some Firmicutes members did not show a clear correlation between 16S rRNA accumulation and DNA copy numbers. However, the prokaryotic acidophile microarray (PAM) analysis showed active members of Alphaproteobacteria in all samples and of Sulfobacillus genus in older ones. Also, new active groups such as Actinobacteria and Acidobacterium genus were detected by PAM. The results suggest that changes during the leaching cycle in chemical and physical conditions, such as pH and Fe3+/Fe2+ ion rate, are primary factors shaping the microbial dynamic in the heap.

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