RETRACTED ARTICLE: Engineering Bacillus licheniformis as a thermophilic platform for the production of l-lactic acid from lignocellulose-derived sugars

Abstract

Background Bacillus licheniformis MW3 as a GRAS and thermophilic strain is a promising microorganism for chemical and biofuel production. However, its capacity to co-utilize glucose and xylose, the major sugars found in lignocellulosic biomass, is severely impaired by glucose-mediated carbon catabolite repression (CCR). In this study, a “dual-channel” process was implemented to engineer strain MW3 for simultaneous utilization of glucose and xylose, using l-lactic acid as a target product.ResultsA non-phosphotransferase system (PTS) glucose uptake route was activated via deletion of the glucose transporter gene ptsG and introduction of the galactose permease gene galP. After replacing the promoter of glucokinase gene glck with the strong promoter P als, the engineered strain recovered glucose consumption and utilized glucose and xylose simultaneously. Meanwhile, to improve the consumption rate of xylose in this strain, several measures were undertaken, such as relieving the regulation of the xylose repressor XylR, reducing the catabolite-responsive element, and optimizing the rate-limiting step. Knockout of ethanol and acetic acid pathway genes further increased lactic acid yield by 6.2%. The resultant strain, RH15, was capable of producing 121.9 g/L l-lactic acid at high yield (95.3%) after 40 h of fermentation from a mixture of glucose and xylose. When a lignocellulosic hydrolysate was used as the substrate, 99.3 g/L l-lactic acid was produced within 40 h, with a specific productivity of 2.48 g/[L h] and a yield of 94.6%.ConclusionsOur engineered strain B. licheniformis RH15 could thermophilically produced l-lactic acid from lignocellulosic hydrolysate with relatively high concentration and productivity at levels that were competitive with most reported cases of l-lactic acid-producers. Thus, the engineered strain might be used as a platform for the production of other chemicals. In addition to engineering the B. licheniformis strain, the “dual-channel” process might serve as an alternative method for engineering a variety of other strains.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0920-z) contains supplementary material, which is available to authorized users.

An efficient CRISPR/Cas9‐based genome editing system for alkaliphilic Bacillus sp. N16‐5 and application in engineering xylose utilization for D‐lactic acid production

“…The RT‐qPCR results showed that genes involved in the xylose degradation pathway were both significantly upregulated in engineered SY‐ldh‐△ xylR , in which the relative transcription levels of xylA and xylB were upregulated by 65‐fold and 27‐fold respectively (Figure 6B ). Nevertheless, it was found that the average xylose consumption rate of SY‐ldh‐△ xylR was 0.338 ± 0.027 g/L/h, which was almost the same as that of SY‐ldh (0.335 ± 0.011 g/L/h) at 11 h (Figure 6C ), which was also reported in B. licheniformis (Li et al, 2017 ) and Clostridium cellulovorans (Wen et al, 2020 ). Therefore, we speculate that the low consumption rate of xylose was probably due to low efficiency of xylose transporters in SY‐ldh‐△ xylR .…”

“…It has been reported that the xylose metabolism negative regulator XylR could specifically repress the gene expression of the xylose pathway in some Gram‐positive organisms (Figure 6A ) (Li et al, 2017 ; Wen et al, 2020 ). To enhance xylose utilization in strain SY‐ldh, xylR was knocked out via CRISPR/Cas9.…”

Retraction Note to: Engineering Bacillus licheniformis as a thermophilic platform for the production of l-lactic acid from lignocellulose-derived sugars

“…The authors are retracting this article because the biological materials were used and the experiments were conducted without proper authorization from the laboratory where these data were obtained [ 1 ].…”

Metabolic engineering of Zymomonas mobilis for co-production of D-lactic acid and ethanol using waste feedstocks of molasses and corncob residue hydrolysate

“…However, these strains cannot utilize lignocellulosic biomass efficiently ( Abedi and Hashemi, 2020 ; Augustiniene et al, 2022 ). Although various metabolic engineering strategies have been applied to produce lactate efficiently from lignocellulosic biomass, such as enhancing the expression or activity of enzymes of lactate biosynthesis pathway, disrupting pathways that compete for carbon substrate, electrons and co-factors, as well as enhancing strain acid-stress tolerance by overexpressing the transporter related genes ( Li et al, 2017 ; Weusthuis et al, 2017 ; Zhang et al, 2017 ; Kong et al, 2019 ; Tsuge et al, 2019 ; Zhu et al, 2019 ), the large-scale industrial production of lactate from cost-effective feedstocks has not yet been commercialized.…”