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 (

Current rehabilitation of coal discard dumps remains a challenge due to reliance on topsoil for establishment of vegetation. Fungcoal has been developed as a viable and alternative strategy for rehabilitation of coal discard dumps and opencast spoils. Fungcoal exploits fungi-plant mutualism to achieve biodegradation of weathered coal, which in turn, promotes reinvigoration of soil components, grass growth and re-vegetation. The main objective of the present study was to determine the effect of different co-substrate materials as carbon donor to support Fungcoal-induced humic acid-like substance enrichment of coal discard at commercial scale. This was achieved by monitoring changes in physicochemical properties of the substrate after Fungcoal application over a three-year period. Results show that where Fungcoal was applied with weathered coal as the carbon donor, and in the absence of added topsoil, it suppressed acidification and salinisation of the coal discard substrate and promoted humic acid-like substance enrichment to support growth and establishment of annual and perennial grasses. In the absence of co-substrate or where highly oxidised coal discard was used as co-substrate, no humic acid-like substance enrichment of the substrate was observed, substrate pH declined, cation exchange capacity and electrical conductivity remained elevated, and re-vegetation failed. The potential of an in situ bioremediation strategy like Fungcoal as an alternative to topsoil is discussed.

A reliance on fossil fuels as a source of energy has resulted in the generation of pollutants which have entered the environment. Health of humans, animals, plants and microorganisms has been compromised due to activities linked to fossil fuel extraction, processing and use. Coal conversion to value added products has been investigated in an effort to reduce the cumulative effects of waste generated during mining. Clean coal technology, developed to convert coal into value added products with reduced pollution, has been a major source of liquid petroleum in South Africa. Although the conversion process, neither generates waste nor pollutes the soil environment, the final products either through accidental or deliberate spillage can have a severe and protracted impact. Biological methods for combating pollutants generated within the fossil fuels sector are preferred to mechanical or physicochemical practices. This is due to the production of non-or less toxic by-products, cost effectiveness and safety. In this manuscript, an overview of the approaches adopted and factors influencing microbial metabolism of fossil fuel contaminants in soil and water bodies is presented. In particular, emphasis is placed on bacteria as biocatalysts of choice and their ability to degrade waste coal and liquid petroleum hydrocarbons.