Quorum Sensing Signaling Molecules Positively Regulate c-di-GMP Effector PelD Encoding Gene and PEL Exopolysaccharide Biosynthesis in Extremophile Bacterium Acidithiobacillus thiooxidans

Abstract

Acidithiobacillus species are fundamental players in biofilm formation by acidophile bioleaching communities. It has been previously reported that Acidithiobacillus ferrooxidans possesses a functional quorum sensing mediated by acyl-homoserine lactones (AHL), involved in biofilm formation, and AHLs naturally produced by Acidithiobacillus species also induce biofilm formation in Acidithiobacillus thiooxidans. A c-di-GMP pathway has been characterized in Acidithiobacillus species but it has been pointed out that the c-di-GMP effector PelD and pel-like operon are only present in the sulfur oxidizers such as A. thiooxidans. PEL exopolysaccharide has been recently involved in biofilm formation in this Acidithiobacillus species. Here, by comparing wild type and ΔpelD strains through mechanical analysis of biofilm-cells detachment, fluorescence microscopy and qPCR experiments, the structural role of PEL exopolysaccharide and the molecular network involved for its biosynthesis by A. thiooxidans were tackled. Besides, the effect of AHLs on PEL exopolysaccharide production was assessed. Mechanical resistance experiments indicated that the loss of PEL exopolysaccharide produces fragile A. thiooxidans biofilms. qRT-PCR analysis established that AHLs induce the transcription of pelA and pelD genes while epifluorescence microscopy studies revealed that PEL exopolysaccharide was required for the development of AHL-induced biofilms. Altogether these results reveal for the first time that AHLs positively regulate pel genes and participate in the molecular network for PEL exopolysaccharide biosynthesis by A. thiooxidans.

Progress in bioleaching: fundamentals and mechanisms of microbial metal sulfide oxidation – part A

“…The construction of an At. thioooxidans Δ pelD null-mutant strain revealed that PEL exopolysaccharide is involved in its biofilm architecture since their biofilms were more sensitive to mechanical stress and easily removable from sulfur upon mechanical stress in comparison to wild-type strains (Díaz et al 2020 ). The analysis of L. ferriphilium DSM 14647 T complete genome sequence showed that cellulose, PEL, and poly-1,6- N -acetyl-D-glucosamine (PGA) can be synthesized by this strain.…”

“…ferrooxidans T (Gonzalez et al 2013 ), while the addition of middle chain AHLs resulted in an enhanced biofilm formation of At. thiooxidans on sulfur surfaces (Díaz et al 2020 ). At least 75 genes have been predicted to be modulated by QS in At.…”

“…It has also been shown that QS and c-di-GMP are connected since a PelD mutant strain of At. thiooxidans displayed changes in its biofilm architecture upon the addition of AHLs, also showing different fluorescent lectin-binding patterns (Díaz et al 2020 ). It has recently been shown that in addition to c-di-GMP, several other messenger nucleotides (cAMP, cGMP, c-di-AMP, and (p)ppGpp) are present in the genomes of acidihiobacilli.…”

Insights into Adaptive Mechanisms of Extreme Acidophiles Based on Quorum Sensing/Quenching-Related Proteins

“…Ultimately, derepressed Clp alters the expression level of abundant genes, such as those coding virulence factors ( 58 ). There is reason to expect that the DSF integrated with c-di-GMP pathways plays pivotal roles in population communication and adaptation, just like the connection between AHL-mediated QS and c-di-GMP during the process of colonization and dissolution of minerals ( 4 , 59 ).…”

Roles and Regulation of Quorum Sensing of Acidophiles in Bioleaching: A Review

“…This locus consists of two convergent genes for the leptospiral lttR and lttI , and a third ORF has been found in the lttIR intergenic region [ 45 ]. A SdiA-like protein has been identified in Acidithiobacillus thiooxidans as strongly likely to take part in QS transcriptional regulation [ 44 ]. SdiA is an orphan QS transcriptional regulator, independent of the AHL synthase.…”