Deciphering the role of Paenibacillus strain Q8 in the organic matter recycling in the acid mine drainage of Carnoulès

Abstract

BackgroundThe recycling of the organic matter is a crucial function in any environment, especially in oligotrophic environments such as Acid Mine Drainages (AMDs). Polymer-degrading bacteria might play an important role in such ecosystem, at least by releasing by-products useful for the rest of the community. In this study, physiological, molecular and biochemical experiments were performed to decipher the role of a Paenibacillus strain isolated from the sediment of Carnoulès AMD.ResultsEven though Paenibacillus sp. strain Q8 was isolated from an oligotrophic AMD showing an acidic pH, it developed under both acidic and alkaline conditions and showed a heterotrophic metabolism based on the utilization of a broad range of organic compounds. It resisted to numerous metallic stresses, particularly high arsenite (As(III)) concentrations (> 1,800 mg/L). Q8 was also able to efficiently degrade polymers such as cellulose, xylan and starch. Function-based screening of a Q8 DNA-library allowed the detection of 15 clones with starch-degrading activity and 3 clones with xylan-degrading activity. One clone positive for starch degradation carried a single gene encoding a "protein of unknown function". Amylolytic and xylanolytic activities were measured both in growing cells and with acellular extracts of Q8. The results showed the ability of Q8 to degrade both polymers under a broad pH range and high As(III) and As(V) concentrations. Activity measurements allowed to point out the constitutive expression of the amylase genes and the mainly inducible expression of the xylanase genes. PACE demonstrated the endo-acting activity of the amylases and the exo-acting activity of the xylanases.ConclusionsAMDs have been studied for years especially with regard to interactions between bacteria and the inorganic compartment hosting them. To date, no study reported the role of microorganisms in the recycling of the organic matter. The present work suggests that the strain Q8 might play an important role in the community by recycling the scarce organic matter (cellulose, hemicellulose, starch...), especially when the conditions change. Furthermore, function-based screening of a Q8 DNA library allowed to assign an amylolytic function to a gene previously unknown. AMDs could be considered as a reservoir of genes with potential biotechnological properties.

Novel and unexpected bacterial diversity in an arsenic-rich ecosystem revealed by culture-dependent approaches

“…The physical and chemical characteristics of the running water were described elsewhere [16]. For this purpose, 11 media corresponding to commonly used media and newly designed FD media were used.…”

Community of thermoacidophilic and arsenic resistant microorganisms isolated from a deep profile of mine heaps

“…Interestingly, most of the microorganisms identified in our work can degrade different complex organic compounds (Leys et al 2004 ; Hadad et al 2005 ; Delavat et al 2012b ). These include Acidovorax spp.…”

“…These bacteria may indirectly affect the overall MS bioleaching process via biological interactions (symbiosis) with the MS biooxidizers, as has been suggested by Watling et al ( 2008 ); e.g., the firmicute Paenibacillus could potentially use sulfur and iron compounds as an energy source (Bond et al 2000 ). Paenibacillus Q8 has polymer-degrading enzymes that confer it cellulolytic, hemicellulolytic and amylolytic activities under a broad pH range (4–10) and under high As(III) and As(V) concentrations (up to 750 and 1,000 mg/L, respectively) (Delavat et al 2012b ).…”

“…Delavat et al ( 2012b ) suggested that “AMDs could be considered as reservoir of genes with potential biotechnological properties”. We share this conclusion for microorganisms resident in mine heaps as described here, with their various metabolic capabilities (Table 3 ).…”

“…Thus, As-bearing phases are generated, and are present in solid and liquid waste from diverse mining processes, including roasting of the powdered enriched ore (producing fine particle waste), conversion of smelting products (dusts), the solvent extraction process (solutions), Cu recovery by refining (electrolytes), precious metals refinery (purges) and heap leaching [acid mine drainage (AMD)]. The concentration of arsenic in AMD, similar to that of mine heaps, may be from 2 to 20 g/L (Santini et al 2000 ; Bednar et al 2002 ; Delavat et al 2012a , b ).…”