Abstract
Coal mining produces large quantities of discard that is stockpiled in large dumps. This stockpiled material, termed coal discard, poses an environmental threat emphasising the need for appropriate bioremediation. Here, metagenomic analysis of the 16S rRNA from ten coal-degrading strains previously isolated from coal slurry from discard dumps and from the rhizosphere of diesel-contaminated sites was used to establish genetic relatedness to known plant growth-promoting (PGP) bacteria in the NCBI database. Measurement of indole and ammonium production and solubilisation of P and K were used to screen bacteria for PGP characteristics. BLAST analysis revealed ≥ 99% homology of six isolates with reference PGP strains of Bacillus, Escherichia, Citrobacter, Serratia, Exiguobacterium and Microbacterium, while two strains showed 94% and 91% homology with Proteus. The most competent PGP strains were Proteus strain ECCN 20b, Proteus strain ECCN 23b and Serratia strain ECCN 24b isolated from diesel-contaminated soil. In response to L-trp supplementation, the concentration of indolic compounds (measured as indole-3-acetic acid) increased. Production of ammonium and solubilisation of insoluble P by these strains was also apparent. Only Serratia strain ECCN 24b was capable of solubilising insoluble K. Production of indoles increased following exposure to increasing aliquots of coal discard, suggesting no negative effect of this material on indole production by these coal-degrading bacterial isolates and that these bacteria may indeed possess PGP characteristics.
Highlights
Coal is a hydrophobic, highly porous and heterogeneous sedimentary rock mined for its energy content
Partial 16S rRNA genomes of varying lengths ranging from 372 to 560 bp were amplified and sequenced from each of the resurrected coal-degrading bacterial strains previously isolated from coal slurry and diesel-contaminated soil
To determine the phylogenetic relationship between coal-degrading bacteria isolated earlier [40] and the diverse array of plant growth-promoting (PGP) bacteria contained in the NCBI GenBank database, basic bioinformatics was used to determine the genetic relatedness of the 16S rRNA gene sequences while conventional biochemical assays were used to screen for putative PGP characteristics
Summary
Highly porous and heterogeneous sedimentary rock mined for its energy content. Mohs for anthracite and classified as naturally recalcitrant [3,4]. It is a complex mixture of aromatic, heterocyclic and aliphatic carbonaceous constituents, the high calorific value. Residual coal and other materials of very low energy content are stockpiled in discard dumps. These discard dumps are numerous and a major source and contributor of pollutants (e.g., particulate matter, heavy metals, acid leachate, etc.) to the surrounding environment including the atmosphere and water bodies and, as a consequence, threaten the environment, human health and quality of life [5,6]. Attempts to stabilise these dumps by cultivation of cover crops does occur once mining is complete [8], a major oversight in developing rehabilitation strategies has been the apparent omission of biotic factors that underpin
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