Biodegradation of lignin via Pseudocitrobacter anthropi MP-4 isolated from the gut of wood-feeding termite Microtermes pakistanicus (Isoptera: termitidae)

Abstract

Symbiotic bacteria in the termite gut system may play an important role in lignin degradation that can assist the subsequent saccharification process. Pseudocitrobacter anthropi MP-4, which is capable of degrading lignin components and rapidly growing on various lignin analogue dyes, was successfully screened from the gut of a wood-feeding termite Microtermes pakistanicus. Further decolorization tests with this strain showed that the strain MP-4 potentially produced some relevant extracellular enzymes to participate in lignin degradation. The removal rate of chemical oxygen demand by this strain was recorded as high as 52.1% when it was incubated in a mineral-salt medium with lignin as the sole carbon source. For the degrading process of MP-4 on lignin, it was proposed through a series of evaluations by field emission scanning electron microscopy, Fourier transform infrared spectroscopy, thermogravimetric analysis, and pyrolysis gas chromatography/mass spectroscopy, that the lignin degradation mechanism of the strain MP-4 would primarily include the cleavage of various chemical linkages and the demethylation reactions. This resulted in a change in the S/G ratio and the disappearance of the biphenyl structure in the lignin components. Thus, these findings suggested that the strain MP-4 uniquely presented an attractive capability to deconstruct lignin components from biomass, which may be potentially valuable for a future industrial exploration.