High tolerance and physiological mechanism of Zymomonas mobilis to phenolic inhibitors in ethanol fermentation of corncob residue

Abstract

Corncob residue as the lignocellulosic biomass accumulated phenolic compounds generated from xylitol production industry. For utilization of this biomass, Zymomonas mobilis ZM4 was tested as the ethanol fermenting strain and presented a better performance of cell growth (2.8 × 10(8) CFU/mL) and ethanol fermentability (54.42 g/L) in the simultaneous saccharification and fermentation (SSF) than the typical robust strain Saccharomyces cerevisiae DQ1 (cell growth of 2.9 × 10(7) CFU/mL, ethanol titer of 48.6 g/L). The physiological response of Z. mobilis ZM4 to the twelve typical phenolic compounds derived from lignocellulose was assayed and compared with that of S. cerevisiae DQ1. Z. mobilis ZM4 showed nearly the same tolerance to the phenolic aldehydes with S. cerevisiae DQ1, but the stronger tolerance to the phenolic acids existing in corncob residue (2-furoic acid, p-hydroxybenzoic acid, p-coumaric acid, vanillic acid, ferulic acid, and syringic acid). The tolerance mechanism of Z. mobilis was investigated in terms of inhibitor degradation, cell morphology and membrane permeability under the stress of phenolics using GC-MS, scanning and transmission electron microscopies (SEM and TEM), as well as fluorescent probes. The results reveal that Z. mobilis ZM4 has the capability for in situ detoxification of phenolic aldehydes, and the lipopolysaccharide aggregation on the cell outer membrane of Z. mobilis ZM4 provided the permeable barrier to the attack of phenolic acids.

Zymomonas mobilis as a model system for production of biofuels and biochemicals

“…Therefore, much effort has focused on exploring new alternative carbon sources, such as lignocellulosic biomass. Besides corn stover that has been used extensively as lignocellulosic biomass, diverse materials including energy crops have been used for ethanol production by Z. mobilis (Zhang and Lynd, ; Behera et al ., ; He et al ., ; Saharkhiz et al ., ; Yang et al ., ; Zhang et al ., ; Peralta‐Contreras et al ., ; Todhanakasem et al ., ; Gu et al ., ; Ma et al ., ; Serate et al ., ; Schell et al ., ; Sulfahri et al ., ); these include energy crops (sugarcane, sugar beet, carob, sweet potato and sweet sorghum), energy plants (e.g. switchgrass), industrial wastes (soybean meal, a co‐product of the production of soybean oil and maize meals), food waste, agricultural residues (corncob residues, rice bran, sweet sorghum stalk, sugarcane molasses, bamboo residues and waste paper sludge), as well as algal biomass from Spirogyra hyalina .…”

Progress and perspective on lignocellulosic hydrolysate inhibitor tolerance improvement in Zymomonas mobilis

“…Using conventional and high-throughput growth assays, effects of inhibitory hydrolysate compounds on Z. mobilis growth and fermentation have been investigated (Dong et al 2013;Franden et al 2009Franden et al , 2013Gu et al 2015;Yi et al 2015). The results demonstrated that acetate, furfural, and phenolic aldehydes are three major inhibitors in the dilute acid-pretreated corn stover hydrolysate for Z. mobilis, and the inhibitory activity was strongly correlated to the hydrophobicity of these compounds.…”

Metabolic engineering of Zymomonas mobilis for 2,3-butanediol production from lignocellulosic biomass sugars

“…Since the genome sequence and functional re-annotation were reported [50, 51], a substantial library of systems biology data as well as several metabolic modeling studies have been accumulated in recent years to better understand the inhibitor tolerance mechanisms of Z. mobilis [52–66]. These inhibitors include the end-product ethanol and toxic compounds from pretreated biomass, such as acetate, furfural, and soluble phenolic compounds.…”