Inhibition analysis of inhibitors derived from lignocellulose pretreatment on the metabolic activity of Zymomonas mobilis biofilm and planktonic cells and the proteomic responses

Abstract

Lignocellulose pretreatment produces various toxic inhibitors that affect microbial growth, metabolism, and fermentation. Zymomonas mobilis is an ethanologenic microbe that has been demonstrated to have potential to be used in lignocellulose biorefineries for bioethanol production. Z. mobilis biofilm has previously exhibited high potential to enhance ethanol production by presenting a higher viable cell number and higher metabolic activity than planktonic cells or free cells when exposed to lignocellulosic hydrolysate containing toxic inhibitors. However, there has not yet been a systematic study on the tolerance level of Z. mobilis biofilm compared to planktonic cells against model toxic inhibitors derived from lignocellulosic material. We took the first insight into the concentration of toxic compound (formic acid, acetic acid, furfural, and 5-HMF) required to reduce the metabolic activity of Z. mobilis biofilm and planktonic cells by 25% (IC₂₅ ), 50% (IC₅₀ ), 75% (IC₇₅ ), and 100% (IC₁₀₀ ). Z. mobilis strains ZM4 and TISTR 551 biofilm were two- to three fold more resistant to model toxic inhibitors than planktonic cells. Synergetic effects were found in the presence of formic acid, acetic acid, furfural, and 5-HMF. The IC₂₅ of Z. mobilis ZM4 biofilm and TISTR 551 biofilm were 57 mm formic acid, 155 mm acetic acid, 37.5 mm furfural and 6.4 mm 5-HMF, and 225 mm formic acid, 291 mm acetic acid, 51 mm furfural and 41 mm 5-HMF, respectively. There was no significant difference found between proteomic analysis of the stress response to toxic inhibitors of Z. mobilis biofilm and planktonic cells on ZM4. However, TISTR 551 biofilms exhibited two proteins (molecular chaperone DnaK and 50S ribosomal protein L2) that were up-regulated in the presence of toxic inhibitors. TISTR 551 planktonic cells possessed two types of protein in the group of 30S ribosomal proteins and motility proteins that were up-regulated.

Keywords: Zymomonas mobilis; inhibitory concentration (IC); lignocellulosic biomass; proteomic; stress response.