The organism is bacterial
Coal is known to be black solid combustible fossil fuel that is made up of carbon based material which is about 50% of its weight. The process of coal formation begins with the decomposition of plant matter by bacterial. The two main phases in coal formation are peatification and coalification, however, bacterial activity creates peat during peatification while increasing the temperature and pressure is refers to as coalification.
Coal is formed from plant vegetation. When this organic matter accumulates (layer after layer) in water-logged region, over time it forms peat (partly decomposed matter in acidic boggy ground). When the peat gets buried down under a column of sediments (over time), the high pressure and temperatures convert the peat to coal.