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Summary: Alicyclobacillus species inhabit diverse environments and have adapted to broad ranges of pH and temperature. However, their adaptive evolutions remain elusive, especially regarding the role of mobile genetic elements (MGEs). Here, we characterized the distributions and functions of MGEs in Alicyclobacillus species across five environments, including acid mine drainage (AMD), beverages, hot springs, sediments, and soils. Nine Alicyclobacillus strains were isolated from AMD and possessed larger genome sizes and more genes than those from other environments. Four AMD strains evolved to be mixotrophic and fell into distinctive clusters in phylogenetic tree. Four types of MGEs including genomic island (GI), insertion sequence (IS), prophage, and integrative and conjugative element (ICE) were widely distributed in Alicyclobacillus species. Further, AMD strains did not possess CRISPR‐Cas systems, but had more GI, IS, and ICE, as well as more MGE‐associated genes involved in the oxidation of iron and sulfide and the resistance of heavy metal and low temperature. These findings highlight the differences in phenotypes and genotypes between strains isolated from AMD and other environments and the important role of MGEs in rapid environment niche expansions. [ABSTRACT FROM AUTHOR]

Acidithiobacillus ferrivorans is an acidophile that often occurs in low temperature acid mine drainage, e.g., that located at high altitude. Being able to inhabit the extreme environment, the bacterium must possess strategies to copy with the survival stress. Nonetheless, information on the strategies is in demand. Here, genomic and transcriptomic assays were performed to illuminate the adaptation mechanisms of an A. ferrivorans strain YL15, to the alpine acid mine drainage environment in Yulong copper mine in southwest China. Genomic analysis revealed that strain has a gene repertoire for metal-resistance, e.g., genes coding for the mer operon and a variety of transporters/efflux proteins, and for low pH adaptation, such as genes for hopanoid-synthesis and the sodium:proton antiporter. Genes for various DNA repair enzymes and synthesis of UV-absorbing mycosporine-like amino acids precursor indicated hypothetical UV radiation—resistance mechanisms in strain YL15. In addition, it has two types of the acquired immune system–type III-B and type I-F CRISPR/Cas modules against invasion of foreign genetic elements. RNA-seq based analysis uncovered that strain YL15 uses a set of mechanisms to adapt to low temperature. Genes involved in protein synthesis, transmembrane transport, energy metabolism and chemotaxis showed increased levels of RNA transcripts. Furthermore, a bacterioferritin Dps gene had higher RNA transcript counts at 6°C, possibly implicated in protecting DNA against oxidative stress at low temperature. The study represents the first to comprehensively unveil the adaptation mechanisms of an acidophilic bacterium to the acid mine drainage in alpine regions. [ABSTRACT FROM AUTHOR]