Cold plasma pretreatment reinforces the lignocellulose-derived aldehyde inhibitors tolerance and bioethanol fermentability for Zymomonas mobilis

Abstract

Background Lignocellulose-derived aldehyde inhibitors seriously blocked the biorefinery of biofuels and biochemicals. To date, the economic production of lignocellulose-based products heavily relied on high productivities of fermenting strains. However, it was expensive and time-consuming for the achievable rational modification to strengthen stress tolerance robustness of aldehyde inhibitors. Here, it aimed to improve aldehyde inhibitors tolerance and cellulosic bioethanol fermentability for the chassis Zymomonas mobilis ZM4 pretreated using energy-efficient and eco-friendly cold plasma. Results It was found that bioethanol fermentability was weaker in CSH (corn stover hydrolysates) than that in synthetic medium for Z. mobilis, and thus was attributed to the inhibition of the lignocellulose-derived aldehyde inhibitors in CSH. Convincingly, it further confirmed that the mixed aldehydes severely decreased bioethanol accumulation through additional aldehydes supplementary assays in synthetic medium. After assayed under different processing time (10–30 s), discharge power (80–160 W), and working pressure (120–180 Pa) using cold atmosphere plasma (CAP), it achieved the increased bioethanol fermentability for Z. mobilis after pretreated at the optimized parameters (20 s, 140 W and 165 Pa). It showed that cold plasma brought about three mutation sites including ZMO0694 (E220V), ZMO0843 (L471L) and ZMO0843 (P505H) via Genome resequencing-based SNPs (single nucleotide polymorphisms). A serial of differentially expressed genes (DEGs) were further identified as the potential contributors for stress tolerance via RNA-Seq sequencing, including ZMO0253 and ZMO_RS09265 (type I secretion outer membrane protein), ZMO1941 (Type IV secretory pathway protease TraF-like protein), ZMOr003 and ZMOr006 (16S ribosomal RNA), ZMO0375 and ZMO0374 (levansucrase) and ZMO1705 (thioredoxins). It enriched cellular process, followed by metabolic process and single-organism process for biological process. For KEGG analysis, the mutant was also referred to starch and sucrose metabolism, galactose metabolism and two-component system. Finally, but interestingly, it simultaneously achieved the enhanced stress tolerance capacity of aldehyde inhibitors and bioethanol fermentability in CSH for the mutant Z. mobilis. Conclusions Of several candidate genetic changes, the mutant Z. mobilis treated with cold plasma was conferred upon the facilitated aldehyde inhibitors tolerance and bioethanol production. This work would provide a strain biocatalyst for the efficient production of lignocellulosic biofuels and biochemicals.

Taurine-mediated gene transcription and cell membrane permeability reinforced co-production of bioethanol and Monascus azaphilone pigments for a newly isolated Monascus purpureus

“…The commercial cellulase was purchased from Sigma-Aldrich (St. Louis, MO, USA) and the filter paper activity was determined as the document [5]. Taurine (HPLC ≥ 98%) was from Yuanye Biotechnology Co., Ltd (Shanghai, China).…”

“…The ethanologenic bacterium Z. mobilis ZM4 (ATCC 31821) was cultured in RM (Rich Medium) medium [5]. A 10 mL RM culture was inoculated in 100 mL RM medium amended with the final concentration of 2.0, 4.0, 6.0 and 8.0 g/L taurine in 250-mL Erlenmeyer flask at 30 °C without shaking.…”

“…Corn stover was pretreated according to the previous study [5]. Enzymatic saccharification assays were carried out at 48 °C for 3 d. CSH contained 46.24 g/L glucose, 16.53 g/L xylose, 0.12 g/L furfural, 0.83 g/L HMF, 0.01 g/L 4-hydroxybenzaldehyde, 0.31 g/L syringaldehyde and 0.09 g/L vanillin.…”

“…Glucose, xylose, ethanol, taurine, furanic aldehydes and phenolic aldehydes were determined following the previous methods [5].…”

“…Therefore, an increasing focus is on the acquirement of the robust strains to augment bioethanol production in biorefinery fields [3]. The classic producers such as Saccharomyces cerevisiae and Zymomonas mobilis are used for bioethanol fermentation with pure sugar and various lignocellulosic biomass [4,5]. However, little was known on bioethanol production of Monascus purpureus.…”