Microbial cell attachment, colonisation and degradation of coal

Abstract

Discoveries of aerobic coal degrading microorganisms have led to their utilisation in various biotechnological coal processes. One promising application of these microbes is the acceleration of coal to methane, which provides an avenue for more sustainable coal usage. However, despite the various findings of coal degraders and related mechanisms, a key aspect in coal degradation, which is cell attachment and colonisation, has been largely neglected. This study is among the first to describe in detail microbial cell attachment and colonisation on coal. Using coal-degrading bacteria and fungi, the initial cell attachment and biofilm formation on coal were investigated across different coal types and conditions. Physico-chemical analyses based on contact angle measurements revealed that hydrophobicity, surface free energy and adhesion thermodynamics, as well as secondary biological and environmental factors, played a crucial role in governing the first form of cell interaction with coal. Direct observation and electron microscopy highlighted different colonisation mechanisms on coal based on cell morphology, surface topography and environmental conditions. Correlations were found between colonisation and degradation of coal, which stressed the importance of cell attachment in coal degradation, although exceptions were present. Another interest of this study was to isolate native coal-degrading fungi for potential field applications. Through multiple coal degradation screenings, Fusarium oxysporum G9o was discovered as a promising bituminous coal-degrading fungus. The isolate showed softening of raw bituminous coal, and infrared analyses revealed oxidation and cleaving mechanisms of coal components. Further, the colonisation of coal by soil communities was monitored through microbial community analyses using Terminal- Restriction Fragment Length Polymorphism (T-RFLP) and pyrosequencing analyses. Unique communities from soil were identified as dominant colonisers on coal, which have not been previously revealed through conventional cultural techniques. Overall, the findings in this study provide valuable insights into the mechanisms of cell attachment and colonisation on coal. This serves as a foundation for a new research area in coal microbiology, which will increase our currently limited understanding on coal-cell interactions.