Investigating the Ligninolytic Potential of Bacteria Isolated from a Decayed Wood Sample in Egypt

Abstract

Lignin is a natural polyphenol material found in complex with cellulose and hemicellulose in every terrestrial and some aquatic plant species. They are recalcitrant and prevent easy access to cellulose; an energy-rich, versatile, promising biomaterial for several eco-friendly and cheap products. The lignin-degrading potential of microbes isolated from degraded wood in an environment in Egypt was investigated. In this study, four bacteria were screened using a methylene blue decolorization test, growth on media with lignin as carbon source, and cellulolytic screening using CMC-Congo red test. The screened isolates were used to treat sorghum stem stalks to ascertain the level of degradation of the lignin content. The four bacterial isolates were positive to the decolorization of methylene blue with percentage decolorization: (23%, 8%, 34%, and 24%) after 24 hrs. respectively. Similarly, the four isolates were able to grow on minimal salt media with lignin as carbon source. The optical densities values measured ranged from (0.030–0.165, −0.040–0.080, 0.040–0.121, −0.039–0.054) after 12 h for the four bacterial isolates, respectively. Also, the four bacterial isolates showed negative results for the cellulase test. FT-IR spectrum for the bacterial-treated sorghum stalks revealed a reduction in peaks at wavelengths indicative of lignin functional groups. Similarly, proximate analysis of the lignocellulose content after treatment recorded were extractives (E) (9, 9, 13.5, 9.5, and 10) %, hemicellulose content (H) (29.5, 26.0, 31, 26, and 30) %, Klason lignin (L) (39, 31, 33, 24, and 26) %, and cellulose (C) (22.2, 33.5, 21.3, 40.5, and 33.5) % for control and the four bacterial isolates, respectively. The p-values estimated from the average values for the extractive and hemicellulose content were not significantly different, whiles that of Lignin and Cellulose was significantly different. The four bacterial isolates showed potential for having ligninolytic enzymes for lignin depolymerization.