Bacterial degradation of coal discard and geologically weathered coal

Abstract

The biodegradation of coal discard is being intensively studied in South Africa in an effort to develop passive methods for the successful revegetation and rehabilitation of waste dumps, to mitigate pollution, and facilitate mine closure. Bacteria were isolated from slurries of coal tailings and diesel-contaminated soil, screened for coal biodegradation competence, characterized, and the colonization and degradation of coal discard and geologically weathered coal investigated using individual isolates and consortia. Ten novel coal-degrading bacterial strains were isolated and characterized, the gene sequences deposited with GenBank, and the (wild-type) strains deposited at Microbial Culture Collection, India. The results from the present work show that bituminous coal discard and geologically weathered coal is used by these isolates as carbon and energy source. Isolated strains and consortia colonized and degraded both coal substrates. Growth rate of the isolates is faster and stationery phase achieved sooner in minimal medium containing geologically weathered coal. This observation suggests that the oxygen-rich weathered coal is a more friable substrate and thus readily colonised and biodegraded. A reduction in mass of substrate is demonstrated for both individual isolates and consortia. The changes in pH and associated media colouration occurred concomitant with formation of humic acid-like (HS) and fulvic acid-like substances (FS) which is confirmed following analysis of these products by FT-IR spectroscopy. It is concluded that preferential metabolism of alkanes from the coal substrates provided the carbon and energy for bacterial growth and transformation of the substrates to HS and FS. Keywords Bacteria Á Biodegradation Á Coal discard Á Humic acid Á Fulvic acid Á FT-IR Á Geologically weathered coal Abbreviations CYP Cytochrome P450 DPA Diphenylamine ECCN EBRU culture collection number FT-IR Fourier transform infrared spectroscopy FA Fulvic acid FS Fulvic acid-like substances HA Humic acid HS Humic acid-like substances LAC Laccase PAH Poly aromatic hydrocarbon Electronic supplementary material The online version of this article (

Coal-Degrading Bacteria Display Characteristics Typical of Plant Growth Promoting Rhizobacteria

“…These isolates were Proteus strain ECCN 20b, Proteus strain ECCN 23b and Serratia strain ECCN 24b. Interestingly, Serratia strain ECCN 24b, either alone or in consort with Citrobacter strain ECCN 19b and Exiguobacterium strain ECCN 21b, was previously shown to be most effective in coal bioconversion [40]. Furthermore, and in corroboration with results from other studies, Serratia strain ECCN 24b was able to solubilise insoluble phosphate [60,61] and potassium [62].…”

“…Databases thus generated yield invaluable information about indicator species [59]. To determine the phylogenetic relationship between coal-degrading bacteria isolated earlier [40] and the diverse array of 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. Strains from seven genera of coal-degrading bacterial isolates utilised in the present study showed ≥ 99% homology with reference gene sequences of PGP bacteria contained in the NCBI GenBank database.…”

“…Bacterial strains used in this study were previously isolated from coal slurry obtained from coal discard dumps at coal mines in Emalahleni (26 • 0 0" S; 29 • 10 0" E), Mpumalanga Province, South Africa, and slurries of material from diesel-contaminated sites (at a depth of~15 cm) collected either from soil at mechanical workshops in Makhanda (33 • 17 0" S; 26 • 31 0" E) or from old tractor engines at a farm in the Makana Local Municipality, Eastern Cape Province, South Africa (Table 1). Details of strain isolation, molecular characterisation, coal biodegrading activity and deposit into an international repository are recounted elsewhere [40].…”

“…Geologically weathered coal was sourced and prepared to yield particles of approximately 0.2-0.5 mm in diameter and sterilised by freeze-thawing using liquid nitrogen as described earlier by Olawale et al [40]. Aliquots of dry sterilised coal (0-1 g) were added directly to seed cultures prepared from stationery phase cells (i.e., OD 600 0.4 after 3 d at 30 • C) of the specified coal-degrading strains.…”

“…An earlier bioprospecting study allowed for selected bacterial isolates with coal biodegradation potential to be characterised [40], but a more detailed biochemical and genetic analysis has yet to be described. Furthermore, screening of these coal-degrading bacteria for plant growth-promoting (PGP) characteristics has not previously been the subject of study.…”