Butanediol production from glycerol and glucose by Serratia marcescens isolated from tropical peat soil

Hybrid Methylotrophic Pathway in Serratia marcescens for Sustainable Terpenoid Biosynthesis

Terpenoids are valuable chemicals used across industries. Methanol, a nonsugar-based feedstock, offers an eco-friendly approach to terpenoid production. In this study, a hybrid methylotrophic pathway was engineered in Serratia marcescens (S. marcescens) HBQA7, which is tolerant to both methanol and terpenoid compounds. The pathway utilizes bacterial methanol dehydrogenase (Mdh) and yeast dihydroxyacetone synthase (Das) to produce monoterpenes and sesquiterpenes from methanol and xylose. 13C labeling experiments identified the optimal enzyme pair: Mdh from Acinetobacter gerneri and Das from Pichia angusta, achieving 7.63% 13C enrichment of the central metabolic intermediate pyruvate. Deletion of pentose phosphate pathway genes (rpiAB) enhanced methanol utilization, achieving 22.99% 13C enrichment. Optimization of the mevalonate (MVA) biosynthetic pathway enabled the production of 5.12 g/L mevalonate in shake flask culture from methanol and xylose. Further construction of a haloarchaea-type MVA pathway enabled the production of geraniol (574.12 mg/L) and (-)-α-bisabolol (1256.41 mg/L) in shake flask cultures. This study demonstrates the first methanol conversion into valuable terpenoids in S. marcescens.

Characterization and Application of a Stationary Phase Promoter Library from Serratia marcescens

Serratia marcescens has garnered increasing attention as a promising host for valuable compound production. However, the lack of an efficient gene regulation toolkit severely hampers its applications. Here, a library of stationary phase promoters was screened in S. marcescens HBA7 using RNA-seq and RT-qPCR, revealing a 43-fold regulatory range with the red fluorescent protein mKate2 as the reporter. The β-galactosidase was employed to demonstrate the universality in driving the expression of different proteins. The wide-ranging utility of these promoters in different hosts was demonstrated in Escherichia coli. Moreover, to assess their potential application, the strongest promoter, P2, was employed to express the swrW gene, resulting in a roughly 20-fold increase in serrawettin W1 production in S. marcescens HBQA7ΔswrW. In summary, this study successfully constructed a gradient-strength stationary phase promoter library, providing an effective toolkit for gene regulation and secondary metabolite production in diverse prokaryotes, including S. marcescens and E. coli.

Carrot Discard as a Promising Feedstock to Produce 2,3-Butanediol by Fermentation with P. polymyxa DSM 365

The valorization of fruit and vegetable residues (such as carrot discard) and their microbial conversion into 2,3-butanediol (BDO) can be considered as a very interesting way to reduce food waste and sustainably originate high value-added products. This work analyzes the valorization of carrot discard as feedstock for 2,3-butanediol (BDO) production by Paenibacillus polymyxa DSM 365. The influences of stirring and the presence of tryptone (nitrogen source) are studied. Furthermore, in order to evaluate the influence of the pre-culture medium (nitrogen source, nutrients, and pH) and the substrate, fermentation assays in simple and mixture semi-defined media (glucose, fructose, and/or galactose) were also carried out. As a result, 18.8 g/L BDO, with a BDO yield of 0.43 g/g (86% of its theoretical value), could be obtained from carrot discard enzymatic hydrolysate at 100 rpm, no tryptone, and pre-culture Häßler medium. No hydrothermal pre-treatment was necessary for BDO production from carrot discard, which increases the profitability of the process. Therefore, 18.8 g BDO, as well as 2.5 g ethanol and 2.1 g acetoin by-products, could be obtained from 100 g of carrot discard (dry matter).