4 hydroxybenzaldehyde

Zymomonas mobilis ZM4 (ATCC 31821) was purchased from American Type Culture Collection (Manassas, VA, USA). Shuttle vector pHW20a was used for construction of Z. mobilis recombinants [15 (link)]. Yeast extract was purchased from Oxoid (Hampshire, UK). Tetracycline (Tc) and nalidixic acid were from Sigma-Aldrich, St. Louis, MO, USA. 4-Hydroxybenzaldehyde, syringaldehyde, and vanillin were from Sangon Biotech Co., Shanghai, China. All other analytical grade chemicals were from Sinopharm Chemical Reagents, Shanghai, China.

Corn stover (CS) was harvested from Dancheng, Henan, China. CS was washed and precipitated to remove the field dirt, sands, metal pieces, and other impurities, and then air-dried to a constant weight. The clean CS was ground coarsely using a beater pulverizer and screened through a mesh with the circle diameter of 10 mm. The raw CS contained 36.2% of cellulose and 19.8% of xylan determined by two-step acid hydrolysis method [39 ]. The cellulase Youtell #6 was purchased from Hunan Youtell Biochemical Co., Yueyang, Hunan, China. The filter paper activity of 63 FPU and the cellobiase activity of 102 CBU per gram of the enzyme were determined according to the methods [40 , 41 ], respectively.
Yeast extract was purchased from Oxiod, Basingstoke, Hampshire, UK. Furfural and 5-hydroxymethylFurfural (HMF) were from J&K Scientific, Beijing, China. 4-Hydroxybenzaldehyde and vanillin were separately from Sangon Biotech and Aladdin Reagents, Shanghai, China. Syringaldehyde was from Alfa Aesar, Heysham, UK. Acetic acid was from Sinopharm Chemical Reagent, Shanghai, China. All other chemicals were purchased from Lingfeng Chemical Reagent Co., Shanghai, China.