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A comprehensive monitoring program has been performed at an industrial bioleaching heap at the Escondida mine in Chile since 2006, in order to study possible changes to the indigenous microbial population. In the initial stage of the bioleaching heap operation, the microbial population was dominated by mesophilic microorganisms. When the height of the heap increased, the microbial population changed from predominantly mesophilic to thermotolerant and moderate thermophilic microorganisms. The results of molecular analyses indicated that under these conditions Leptospirillum ferriphilum and Sulfobacillus thermosulfidooxidans are the most abundant microorganisms. Those results obtained show that the highest ferrous iron oxidation activity at the third lift occurs at the same operational temperature window as that of the thermotolerant and moderate thermophiles. An increase in the expression of genes (including rfa F1) associated with cell envelope biogenesis was indicative of the active growth of L. ferriphilum . We conclude that the increasing heap height and the consequent increase in temperature within the heap triggered a change in the microbial community from mesophilic to moderate thermophilic microorganisms. Further, this shift had a relevant impact on the metallurgical performance of the industrial bioheap process at Escondida mine. [ABSTRACT FROM AUTHOR]

Highlights: [•] Genetic diversity of rhizobia present in nodules of beans in two Chilean soils is very low. [•] The genetic diversity was independent of soil origin and previous use. [•] Indigenous rhizobial populations play a minor role symbiotic partner selection. [Copyright &y& Elsevier]

Martian surface microbial inhabitants would be challenged by a constant and unimpeded flux of UV radiation, and the study of analog model terrestrial environments may be of help to understand how such life forms could survive under this stressful condition. One of these environments is the Atacama Desert (Chile), a well-known Mars analog due to its extreme dryness and intense solar UV radiation. Here, we report the microbial diversity at five locations across this desert and the isolation of UVC-tolerant microbial strains found in these sites. Denaturing gradient gel electrophoresis (DGGE) of 16S rDNA sequences obtained from these sites showed banding patterns that suggest distinct and complex microbial communities. Analysis of 16S rDNA sequences obtained from UV-tolerant strains isolated from these sites revealed species related to the Bacillus and Pseudomonas genera. Vegetative cells of one of these isolates, Bacillus S3.300-2, showed the highest UV tolerance profile (LD = 318 J m), tenfold higher than a wild-type strain of Escherichia coli. Thus, our results show that the Atacama Desert harbors a noteworthy microbial community that may be considered for future astrobiological-related research in terms of UV tolerance. [ABSTRACT FROM AUTHOR]