Abstract
Bioleaching of metal sulfide ores involves acidophilic microbes that catalyze the chemical dissolution of the metal sulfide bond that is enhanced by attached and planktonic cell mediated oxidation of iron(II)-ions and inorganic sulfur compounds. Leptospirillum spp. often predominate in sulfide mineral-containing environments, including bioheaps for copper recovery from chalcopyrite, as they are effective primary mineral colonizers and oxidize iron(II)-ions efficiently. In this study, we demonstrated a functional diffusible signal factor interspecies quorum sensing signaling mechanism in Leptospirillum ferriphilum and Leptospirillum ferrooxidans that produces (Z)-11-methyl-2-dodecenoic acid when grown with pyrite as energy source. In addition, pure diffusible signal factor and extracts from supernatants of pyrite grown Leptospirillum spp. inhibited biological iron oxidation in various species, and that pyrite grown Leptospirillum cells were less affected than iron grown cells to self inhibition. Finally, transcriptional analyses for the inhibition of iron-grown L. ferriphilum cells due to diffusible signal factor was compared with the response to exposure of cells to N- acyl-homoserine-lactone type quorum sensing signal compounds. The data suggested that Leptospirillum spp. diffusible signal factor production is a strategy for niche protection and defense against other microbes and it is proposed that this may be exploited to inhibit unwanted acidophile species.
Highlights
Bioleaching of metal sulfide ores involves acidophilic microbes that catalyze the chemical dissolution of the metal sulfide bond that is enhanced by attached and planktonic cell mediated oxidation of iron(II)-ions and inorganic sulfur compounds
The industrial process of biomining describes the use of acidophilic microbes for the recovery of metals from sulfide ores. It includes bioleaching when the target metal is part of the metal sulfide mineral and biooxidation when the target metal is trapped as microscopic particles within the mineral matrix. Both processes are mediated by chemical dissolution of the metal sulfide bond that is enhanced by microbial oxidation of iron(II)-ions and inorganic sulfur compounds (ISCs)
SPIII/3 and the increase of c-di-GMP levels measured in At. ferrooxidans ATCC 23270T cells adhering to solid substrates suggests a connection between acyl homoserine lactones (AHLs) mediated Quorum sensing (QS) and the c-di-GMP p athways[20,24,26,30,31]
Summary
Bioleaching of metal sulfide ores involves acidophilic microbes that catalyze the chemical dissolution of the metal sulfide bond that is enhanced by attached and planktonic cell mediated oxidation of iron(II)-ions and inorganic sulfur compounds. Leptospirillum species are efficient biofilm forming strains on pyrite and chalcopyrite[15] due to high amounts of EPS embedding attached cells to the mineral s urface[12,16,17] It is unknown if other factors may influence mineral colonization by Leptospirillum, making them crucial for understanding cell attachment and biofilm formation on metal sulfides. SPIII/3 and the increase of c-di-GMP levels measured in At. ferrooxidans ATCC 23270T cells adhering to solid substrates suggests a connection between AHL mediated QS and the c-di-GMP p athways[20,24,26,30,31] Another type of QS based system relies on diffusible signal factors (DSF) from a family of cis-2-unsaturated fatty acid signal compounds and DSF family signal sensing is known to act directly on c-di-GMP metabolism[32,33]. We hypothesize that Leptospirillum species produce DSF-family signal molecules and that they are involved in regulating biofilm formation and bioleaching of metal sulfide ores
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