Abstract
An understanding of biofilm formation is relevant to the design of biological strategies to improve the efficiency of the bioleaching process and to prevent environmental damages caused by acid mine/rock drainage. For this reason, our laboratory is focused on the characterization of the molecular mechanisms involved in biofilm formation in different biomining bacteria. In many bacteria, the intracellular levels of c-di-GMP molecules regulate the transition from the motile planktonic state to sessile community-based behaviors, such as biofilm development, through different kinds of effectors. Thus, we recently started a study of the c-di-GMP pathway in several biomining bacteria including Acidithiobacillus caldus. C-di-GMP molecules are synthesized by diguanylate cyclases (DGCs) and degraded by phosphodiesterases (PDEs). We previously reported the existence of intermediates involved in c-di-GMP pathway from different Acidithiobacillus species. Here, we report our work related to At. caldus ATCC 51756. We identified several putative-ORFs encoding DGC and PDE and effector proteins. By using total RNA extracted from At. caldus cells and RT-PCR, we demonstrated that these genes are expressed. We also demonstrated the presence of c-di-GMP by mass spectrometry and showed that genes for several of the DGC enzymes were functional by heterologous genetic complementation in Salmonella enterica serovar Typhimurium mutants. Moreover, we developed a DGC defective mutant strain (Δc1319) that strongly indicated that the c-di-GMP pathway regulates the swarming motility and adherence to sulfur surfaces by At. caldus. Together, our results revealed that At. caldus possesses a functional c-di-GMP pathway which could be significant for ores colonization during the bioleaching process.
Highlights
Acidithiobacillus caldus is an acidophilic, Gram-negative bacterium which gains energy by oxidation of elemental sulfur and reduced inorganic sulfur compounds [1]
An understanding of the number of genes involved in the c-di-GMP metabolism and their role in various environments faced by different bacteria is still lacking
In Vibrio cholerae in which c-di-GMP plays a key role in regulating changes in gene expression that occur during the shift from aquatic to host environments, 61 proteins (12 EAL, 30 GGDEF, 9 HD-GYP, and 10 GGDEF-EAL) related to c-di-GMP metabolism have been identified [79,80]
Summary
Acidithiobacillus caldus is an acidophilic, Gram-negative bacterium which gains energy by oxidation of elemental sulfur and reduced inorganic sulfur compounds [1]. Unlike others members of the Acidithiobacillus genus (At. ferrooxidans, At. thiooxidans, At. albertensis, At. ferrivorans and At. ferridurans), At. caldus is moderately thermophilic [1]. It has been isolated from many commercial biomining plants [2,3,4,5], together with the iron oxidizing bacteria belonging to the genus Leptospirillum, and dominates bacterial populations in processes operating within the temperature range of 35–50°C [2]. Ore dissolution can be achieved by two pathways, in which iron and sulfur oxidizing bacteria have specific roles [6,7,8]. Even though a chemotactic response to sulfur gradients has been suggested [9], molecular mechanisms involved in the transition from planktonic to attached state by At. caldus are still unknown
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