Fungal colonization and enzyme-mediated metabolism of waste coal by Neosartorya fischeri strain ECCN 84

Biotechnology of Microorganisms from Coal Environments: From Environmental Remediation to Energy Production

Simple Summary

Despite the wide perception that coal environments are extreme habitats, they harbor resident microbial communities. Coal-associated habitats, such as coal mine areas/drainages, spoil heaps, and coalbeds, are defined as complex ecosystems with indigenous microbial groups and native microecological networks. Resident microorganisms possess rich functional potentials and profoundly shape a range of biotechnological processes in the coal industry, from production to remediation.

Abstract

It was generally believed that coal sources are not favorable as live-in habitats for microorganisms due to their recalcitrant chemical nature and negligible decomposition. However, accumulating evidence has revealed the presence of diverse microbial groups in coal environments and their significant metabolic role in coal biogeochemical dynamics and ecosystem functioning. The high oxygen content, organic fractions, and lignin-like structures of lower-rank coals may provide effective means for microbial attack, still representing a greatly unexplored frontier in microbiology. Coal degradation/conversion technology by native bacterial and fungal species has great potential in agricultural development, chemical industry production, and environmental rehabilitation. Furthermore, native microalgal species can offer a sustainable energy source and an excellent bioremediation strategy applicable to coal spill/seam waters. Additionally, the measures of the fate of the microbial community would serve as an indicator of restoration progress on post-coal-mining sites. This review puts forward a comprehensive vision of coal biodegradation and bioprocessing by microorganisms native to coal environments for determining their biotechnological potential and possible applications.

Elaboration of a Phytoremediation Strategy for Successful and Sustainable Rehabilitation of Disturbed and Degraded Land

Humans are dependent upon soil which supplies food, fuel, chemicals, medicine, sequesters pollutants, purifies and conveys water, and supports the built environment. In short, we need soil, but it has little or no need of us. Agriculture, mining, urbanization and other human activities result in temporary land-use and once complete, used and degraded land should be rehabilitated and restored to minimize loss of soil carbon. It is generally accepted that the most effective strategy is phyto-remediation. Typically, phytoremediation involves re-invigoration of soil fertility, physicochemical properties, and its microbiome to facilitate establishment of appropriate climax cover vegetation. A myco-phytoremediation technology called Fungcoal was developed in South Africa to achieve these outcomes for land disturbed by coal mining. Here we outline the contemporary and expanded rationale that underpins Fungcoal, which relies on in situ bio-conversion of carbonaceous waste coal or discard, in order to explore the probable origin of humic substances (HS) and soil organic matter (SOM). To achieve this, microbial processing of low-grade coal and discard, including bio-liquefaction and bio-conversion, is examined in some detail. The significance, origin, structure, and mode of action of coal-derived humics are recounted to emphasize the dynamic equilibrium, that is, humification and the derivation of soil organic matter (SOM). The contribution of plant exudate, extracellular vesicles (EV), extra polymeric substances (EPS), and other small molecules as components of the dynamic equilibrium that sustains SOM is highlighted. Arbuscular mycorrhizal fungi (AMF), saprophytic ectomycorrhizal fungi (EMF), and plant growth promoting rhizobacteria (PGPR) are considered essential microbial biocatalysts that provide mutualistic support to sustain plant growth following soil reclamation and restoration. Finally, we posit that de novo synthesis of SOM is by specialized microbial consortia (or ‘humifiers’) which use molecular components from the root metabolome; and, that combinations of functional biocatalyst act to re-establish and maintain the soil dynamic. It is concluded that a bio-scaffold is necessary for functional phytoremediation including maintenance of the SOM dynamic and overall biogeochemistry of organic carbon in the global ecosystem

Development of a saprophytic fungal inoculum for the biodegradation of sub-bituminous coal

The rhizospheres of the weeds Ageratum conyzoides, Axonopus compressus, Emilia coccinea, Synedrella nodiflora, Urena lobata and Sida acuta from a sub-bituminous coal mining site and a control site, without coal discards, were screened for new fungi with ability to degrade sub-bituminous coal in the laboratory. The isolates were identified by cultural and molecular methods. Seventeen out of the sixty-one fungal isolates tested could utilize sub-bituminous coal as an energy source. Upon further evaluation, only seven of these were promising candidates for coal biodegradation, and they were assayed for their biosolubilization and depolymerization activities to determine their mechanisms of coal biodegradation. Based on the accumulation of humic acid (HA), which is the marker for biosolubilization, Mucor circinelloides and Aspergillus tubingensis were the most active. On the other hand, Cunninghamella bertholletiae, Simplicillium subtropicum, Penicillium daleae and Trichoderma koningiopsis were the highest producers of fulvic acid (FA), the indicator of depolymerization. Purpureocillium lilacinum produced the lowest yields of both HA and FA compared to the other six coal-degrading candidates. The presence of laccase in Trichoderma koningiopsis, Penicillium daleae and Simplicillium subtropicum suggests a role for this enzyme in the enhancement of the coal biodegradation process. However, the inability to amplify the laccase gene in Cunninghamella bertholletiae indicates that another enzyme probably aids its coal bioconversion. The current investigation highlights the potentials of these strains in harnessing biotechnological processes of sub-bituminous coal conversion into value-added products, which could be extended to the bioremediation of coal-polluted soils. The fungi with the highest coal bioconversion capabilities belonged to Ascomycota and Zygomycota and were found in the rhizospheres of the weeds Emilia coccinea, Ageratum conyzoides and Axonopus compressus.

Biogenic formation of amorphous carbon by anaerobic methanotrophs and select methanogens

Elemental carbon exists in different structural forms including graphite, diamond, fullerenes, and amorphous carbon. In nature, these materials are produced through abiotic chemical processes under high temperature and pressure but are considered generally inaccessible to biochemical synthesis or breakdown. Here, we identified and characterized elemental carbon isolated from consortia of anaerobic methanotrophic archaea (ANME) and sulfate-reducing bacteria (SRB), which together carry out the anaerobic oxidation of methane (AOM). Two different AOM consortia, ANME-1a/HotSeep-1 and ANME-2a/c/Seep-SRB, produce a black material with similar characteristics to disordered graphite and amorphous carbon. Stable isotope probing studies revealed that the carbon is microbially generated during AOM. In addition, we found that select methanogens also produce amorphous carbon with similar characteristics to the carbon from AOM consortia. Biogenic amorphous carbon may serve as a conductive element to facilitate electron transfer, or redox active functional groups associated with the carbon could act as electron donors and acceptors.

Bioconversion of coal to methane by microbial communities from soil and from an opencast mine in the Xilingol grassland of northeast China

BACKGROUND

The Xilingol grassland ecosystem has abundant superficial coal reserves. Opencast coal mining and burning of coal for electricity have caused a series of environmental challenges. Biogenic generation of methane from coal possesses the potential to improve economic and environmental outcomes of clean coal utilization. However, whether the microbes inhabiting the grassland soil have the functional potential to convert coal into biomethane is still unclear.

RESULTS

Microbial communities in an opencast coal mine and in grassland soil covering and surrounding this mine and their biomethane production potential were investigated by Hiseq sequencing and anaerobic cultivation. The microbial communities in covering soil showed high similarity to those in the surrounding soil, according to the pairwise weighted UniFrac distances matrix. The majority of bacterial communities in coal and soil samples belonged to the phyla Firmicutes, Bacteroidetes, Actinobacteria and Proteobacteria. The dominant bacterial genera in grassland soil included Gaiella, Solirubrobacter, Sphingomonas and Streptomyces; whereas, the most abundant genus in coal was Pseudarthrobacter. In soil, hydrogenotrophic Methanobacterium was the dominant methanogen, and this methanogen, along with acetoclastic Methanosarcina and methylotrophic Methanomassiliicoccus, was detected in coal. Network-like Venn diagram showed that an average of 28.7% of microbial communities in the samples belonged to shared genera, indicating that there is considerable microbial overlap between coal and soil samples. Potential degraders and methanogens in the soil efficiently stimulated methane formation from coal samples by the culturing-based approach. The maximum biogenic methane yields from coal degradation by the microbial community cultured from grassland soil reached 22.4 μmol after 28 day.

CONCLUSION

The potential microbial coal degraders and methanogenic archaea in grassland soil were highly diverse. Significant amounts of biomethane were generated from coal by the addition of grassland soil microbial communities. The unique species present in grassland soil may contribute to efficient methanogenic coal bioconversion. This discovery not only contributes to a better understanding of global microbial biodiversity in coal mine environments, but also makes a contribution to our knowledge of the synthetic microbiology with regard to effective methanogenic microbial consortia for coal degradation.

Improvement of efficiency of brown coal biosolubilization by novel recombinant Fusarium oxysporum laccase

Clean coal technologies (e.g. coal biosolubilization) are of essential value, especially in Europe, where coal is the national wealth and other energy sources like crude oil are not available. Fusarium oxysporum LOCK 1134, the strain isolated from brown coal, efficiently biosolubilizes lignite. The obtained liquefied products contain 50% less sulfur and over 99% less mercury than the crude coal. Moreover, the liquefied coal can be modified further by laccase. In this study F. oxysporum laccase was expressed in Pichia pastoris for the first time and was assessed as an additional agent for coal degradation. The novel laccase contributes to humic and fulvic acids release from liquefied coal due to introduction of oxygen into coal structure. The effect is increased when a natural redox mediator, sinapic acid, is present in the reaction mixture-up to 30% and 80% respectively. Humic acids obtained by biological process are environmentally friendly fertilizers that may have stimulating effects on crop growth.