The dynamics of two iron-oxidizing Acidithiobacillus strains in industrial copper sulfide heap-leaching.

Several species within the Acidithiobacillus (At.) genus can derive energy from oxidizing ferrous iron and sulfur. Two bacterial strains according to their 16S rRNA gene sequences closely related to At. ferridurans and At. ferrivorans were obtained from the industrial sulfide heap leaching process at Minera Escondida (SLH), named D2 and DM, respectively. We applied statistical and data mining analyses to the abundance of At. ferridurans D2 and At. ferrivorans DM taxa in the industrial process over 16 years of operation. In addition, we performed phylogenetic analysis and genome comparison of the type strains, as well as culturing approaches with representative isolates of At. ferridurans D2 and At. ferrivorans DM taxa to understand the differential phenotypic features. Throughout the 16 years, two main operational stages were identified based on the D2 and DM taxa predominance in solution samples. The better suitability of At. ferrivorans DM to grow in a wide range of temperature and in micro-oxic environments, and to oxidize S by reducing Fe(III) revealed through culturing approaches can, in a way, explain the taxa distribution in both operational stages. The isolate At. ferridurans D2 could be considered as a specialist in aerobic sulfur oxidation, while isolate At. ferrivorans DM is a specialist in iron oxidation. In addition, the results from ore samples occasionally obtained from the industrial heap suggest that At. ferridurans D2 abundance was more related to its abundance in the solution samples than At. ferrivorans DM was. This dynamic coincides with previously obtained results in in-lab cell-mineral attaching experiments with both strains. This information increases our knowledge the ecophysiology of Acidithiobacillus and of the importance of diverse physiological traits at industrial bioleaching scales.

Hyperarid soil microbial community response to simulated rainfall.

The exceptionally long and protracted aridity in the Atacama Desert (AD), Chile, provides an extreme, terrestrial ecosystem that is ideal for studying microbial community dynamics under hyperarid conditions. Our aim was to characterize the temporal response of hyperarid soil AD microbial communities to ex situ simulated rainfall (5% g water/g dry soil for 4 weeks) without nutrient amendment. We conducted replicated microcosm experiments with surface soils from two previously well-characterized AD hyperarid locations near Yungay at 1242 and 1609 masl (YUN1242 and YUN1609) with distinct microbial community compositions and average soil relative humidity levels of 21 and 17%, respectively. The bacterial and archaeal response to soil wetting was evaluated by 16S rRNA gene qPCR, and amplicon sequencing. Initial YUN1242 bacterial and archaeal 16S rRNA gene copy numbers were significantly higher than for YUN1609. Over the next 4 weeks, qPCR results showed significant increases in viable bacterial abundance, whereas archaeal abundance decreased. Both communities were dominated by 10 prokaryotic phyla (Actinobacteriota, Proteobacteria, Chloroflexota, Gemmatimonadota, Firmicutes, Bacteroidota, Planctomycetota, Nitrospirota, Cyanobacteriota, and Crenarchaeota) but there were significant site differences in the relative abundances of Gemmatimonadota and Chloroflexota, and specific actinobacterial orders. The response to simulated rainfall was distinct for the two communities. The actinobacterial taxa in the YUN1242 community showed rapid changes while the same taxa in the YUN1609 community remained relatively stable until day 30. Analysis of inferred function of the YUN1242 microbiome response implied an increase in the relative abundance of known spore-forming taxa with the capacity for mixotrophy at the expense of more oligotrophic taxa, whereas the YUN1609 community retained a stable profile of oligotrophic, facultative chemolithoautotrophic and mixotrophic taxa. These results indicate that bacterial communities in extreme hyperarid soils have the capacity for growth in response to simulated rainfall; however, historic variations in long-term hyperaridity exposure produce communities with distinct putative metabolic capacities.

Corrigendum: Hyperarid soil microbial community response to simulated rainfall.

[This corrects the article DOI: 10.3389/fmicb.2023.1202266.].