Coordinated lignocellulolysis: First record of “lignin-first, cellulose-second” type synergy in Klebsiela–Enterobacter-mediated rice straw degradation via surface delignification and cellulose crystallinity modulation

Surface sterilized Oryza sativa AT362 straw was screened for endophytic ligninolytic and cellulolytic bacteria using Colour Unit reduction and Congo Red decolorization assays. Ligninolytic Klebsiella variicola AKL1104 and cellulolytic Enterobacter chuandaensis AKC1108, biocompatible, were inoculated at 1:1 ratio and incubated in 1% (w/v) rice straw broth at 37 °C for 7 d. Topological changes due to degradation were conducted using scanning electron microscopy (SEM), X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), X-ray photoelectron spectroscopy (XPS) for 9 d. During t = 9 d, SEM shows vascular tissue perforation with tunnels, indicating K. variicola mediated-delignification, allowing E. chuandaensis to sequentially degrade cellulose. XRD revealed a cellulose crystallinity declined from 30.08% on t = 0 d to 11.76% on t = 9 d. Electron microscopy and crystallite size calculations in t = 6 d (6.81 nm) and t = 9 d (90.16 nm) indicate self-assembly of cellulose fibrils. FTIR and XPS analysis indicated crystalline cellulose transformation to amorphous as the lateral order index dropped from 0.776 ± 0.006 to 0.503 ± 0.007, while surface lignin coverage was reduced from 5.01% to 2.20%, respectively.