Cyclic di-GMP signaling in extreme Acidophilic bacteria

Extreme acidophilic bacteria are a phylogenetically diverse group of microorganisms that grow optimally at pH values below 3. They thrive in natural or man-made environments where life is challenged by extreme acidity, low availability of organic matter, and high concentrations of heavy metals. Most acidophilic bacteria are chemolitho(auto)trophs, obtaining energy from the oxidation of metal sulfides, one of the most abundant mineral classes on earth. Bacterial attachment on mineral surface and the subsequent biofilm development plays critical role in mineral dissolution, which is directly related with ecologic phenomena and biotechnological applications, such as acid mine drainage, biogeochemical cycles, and bioleaching processes. In contrast to well-studied neutrophilic bacterial strains, the understanding of cyclic di-GMP signaling in extreme acidophilic bacteria is still incipient. However, significant progress has been made in the last several years through global genomic analysis on acidophilic communities, and genetic work on species belonging to the most iconic acidophilic genus, Acidithiobacillus. This chapter presents an overview of molecular insights into cyclic di-GMP signaling obtained from At. ferrooxidans, At. caldus, and At. thioooxidans. In addition, it describes the cyclic di-GMP signaling network as a widespread but highly diverse mechanism used by acidophilic bacteria to transduce environmental signals into biofilm-related responses mainly driven by cyclic di-GMP effector proteins involved in swarming motility and the production of exopolymeric substances.