Phyto‐bioconversion of hard coal in the Cynodon dactylon/coal rhizosphere

Abstract

Fundamental processes involved in the microbial degradation of coal and its derivatives have been well documented. A mutualistic interaction between plant roots and certain microorganisms to aid growth of plants such as Cynodon dactylon (Bermuda grass) on hard coal dumps has recently been suggested. In the present study coal bioconversion activity of nonmycorrhizal fungi was investigated in the C. dactylon/coal rhizosphere. Fungal growth on 2% Duff-agar, gutation formation on nitric acid treated coal and submerged culture activity in nitrogen-rich and -deficient broth formed part of the screening and selection of the fungi. The selected fungal isolates were confirmed to be found in pristine C. dactylon/coal rhizosphere. To simulate bioconversion, a fungal aliquot of this rhizosphere was used as inoculum for a Perfusate fixed bed bioreactor, packed with coal. The results demonstrate an enhanced coal bioconversion facilitated by low molecular weight organics and the bioconversion of coal may be initiated by an introduction of nitrogen moieties to the coal substrate. These findings suggest a phyto-bioconversion of hard coal involving plant and microbes occurring in the rhizosphere to promote the growth of C. dactylon. An understanding of this relationship can serve as a benchmark for coal dumps rehabilitation as well as for the industrial scale bioprocessing of hard coal.

Biological conversion of low-grade coal discard to a humic substance-enriched soil-like material

“…Neosartorya fischeri strain ECCN84, isolated from different coal environments around South Africa (Igbinigie et al 2008(Igbinigie et al , 2010 and strains PPRI5328 (Phanerocheate chrysosporium) and PPRI4835 (Coriolus versicolor), obtained from the Agricultural Research Council (ARC, South Africa), were re-cultured on plates of 2.5% PDA at 26°C. All fungi used as inoculum tested positive for production of the ligninolytic enzymes LAC and MnP on PDA with added 2.6-dimethoxy phenol, 2.2 0 [azino-bis-(3-ethylbonzthiazoline-6-sulphonic acid) diammonium salt] (ABTS) at 37°C (Table S1) using the protocols described by Pointing (1999).…”

“…C. dactylon was observed growing intermittently on dumps of bituminous hard coal discard that had not undergone any form of rehabilitation (Igbinigie et al 2008(Igbinigie et al , 2010. Further studies revealed the potential of a geologically weathered coal to sustain plant growth while investigation of the root zone indicated the presence of a diverse fungal flora.…”

“…An extensive screening exercise followed and resulted in the isolation of among other fungi, the ascomycete Neosartorya fischeri (Igbinigie et al 2008). This fungus was shown to actively degrade coal in a perfusion fixed-bed bioreactor, used to simulate the coal discard dump environment (Igbinigie et al 2008), in the C. dactylon/coal rhizosphere (Igbinigie et al 2010;Mukasa-Mugerwa et al 2010), and in vitro (Sekhohola et al 2014). Based on these findings, an integrated model was proposed to describe some of the interactions in the rhizosphere that transform coal discard to a humic acid-like substance (HS) enriched medium capable of supporting establishment of a healthy vegetation (Sekhohola et al 2013).…”

Geochemical Study of Weathered Coal, a Co-Substrate for Bioremediation of South African Coal Discard Dumps

“…Over the years, it has become increasingly important to gain better insight into the molecular structure and mineral matter of coal, for both coal beneficiation and to mitigate detrimental effects from its use and storage. More emphasis has since been placed on the chemical structure using techniques such as pyrolysis-gas chromatography-mass spectrometry (pyr-GC-MS) [14,15], and nuclear magnetic resonance (NMR) spectrometric analysis [16][17][18][19][20][21][22], among others. Interest in lower-grade coal has also increased because of its potential as a soil amendment product which has particular relevance to the work described here.…”

“…Indeed, other forms of weathered coal including coal from discard dumps and a highly oxidized coal obtained from an aged waste dump were unable to support fungal-plant bioremediation and revegetation [20]. Thus, the geochemical study of outcrop-weathered coal described here was undertaken to provide insight into the role of this material as a mineral/carbon source to ensure biologically induced humic acid (HA)-like substance enrichment of discard and spoil to facilitate breakdown of the carbonaceous material [21][22][23], plant-fungal mutualism [24,25], and revegetation without the need for topsoil [20,26]. Furthermore, a good understanding of the geochemistry of this outcrop weathered coal may improve our understanding of the geological processes involved in coal weathering in situ.…”