Production of 2,3-butanediol byKlebsiella oxytocafrom various sugars in microalgal hydrolysate

Molecular analysis of sugar transporters and glycolysis pathways in Ettlia sp. under heterotrophy using fructose and glucose

Fructophilic behavior in microalgae is a rare trait that could benefit biorefineries by enabling substitution of carbon source with fructose, and our previous study identified that Ettlia sp. prefers fructose relative to glucose. In this study, by analyzing the transcription levels of genes related to sugar transport and the glycolysis pathway, the fructose utilization of Ettlia sp. was investigated. In a fructose-containing medium, the expression levels of fructokinase (EttFRK3) and glucokinase (EttGCK1 and EttGCK2) genes were significantly upregulated in heterotrophic cultivation of Ettlia sp. under fructose supplementation conditions. Further, a sugar transporter (EttSTF11) was significantly upregulated by 3.2-fold in 1 day, and this increase was analogous to the specific growth rate exhibited by the species. Subsequent cultivation tests with multi-sugar sources also showed a significant upregulation of EttSTF11 relative to other treatments without fructose. A phylogenetic tree derived from the analysis of different transporters of interest identified that EttSTF11 was adjacent to reference fructose transporters with a high bootstrap value of 71. Given that the transmembrane domains of EttSTF11 were analogous to those of reference fructose transporter genes, EttSTF11 appeared to play a critical role in fructose consumption and metabolism in Ettlia sp.

Metabolic regulation and optimization of oxygen supply enhance the 2,3-butanediol yield of the novel Klebsiella sp. isolate FSoil 024

BACKGROUND

Biogenic 2,3-butanediol (2,3-BDO) is a high-value-added compound that can be used as a liquid fuel and a platform chemical. Bioproduction of 2,3-BDO is an environmentally friendly choice.

METHOD AND RESULTS

Three recombinant derivatives of the novel Klebsiella sp. isolate FSoil 024 (WT) were constructed via different strategies including deletion of lactate dehydrogenase by λ-Red homologous recombination technology, overexpression of the small-noncoding RNA RyhB and a combination of both. The 2,3-BDO productivity of the mutants increased by 61.3-79%, and WT-Δldh/ryhB displayed the highest 2,3-BDO yield of 42.36 mM after 24 h of shake-flask fermentation. Glucose was shown as the best carbon source for 2,3-BDO production by WT-Δldh/ryhB. In addition, higher oxygenation was favorable for ideal product synthesis. The maximal 2,3-BDO yield of WT and WT-Δldh/ryhB were increased by 23.3 and 52.5% respectively compared to the control group in the presence of 70% oxygen (V:V' = O₂ :(O₂ +N₂ )).

CONCLUSION AND IMPLICATIONS

According to the present study, deletion of lactate dehydrogenase, RyhB overexpression and manipulation of oxygen supply showed great impacts on cell growth, 2,3-BDO productivity and cellular metabolism of the novel isolated strain Klebsiella sp. FSoil 024. This work would also provide insights for promoting 2,3-BDO biosynthesis for industrial applications. This article is protected by copyright. All rights reserved.

High 2,3-butanediol production from glycerol by Raoultella terrigena CECT 4519

Bioconversion of biodiesel-derived glycerol into 2,3-butanediol has received recently much attention due to its increasing surplus and its multiple uses in industry as bulk chemical. The influence of initial glycerol concentration on 2,3-butanediol production in batch runs has been studied. A concentration higher than 140 g/L produces an inhibitory effect on the final 2,3-butanediol concentration and its production rate. In batch mode, the highest yield respect to the theoretical maximum yield (71%) was reached employing 140 g/L as initial concentration 140 g/L. Based on these results, a high 2,3-butanediol production has been achieved through a fed-batch strategy. The reached 2,3-butanediol concentration was 90.5 g/L from pure glycerol and 80.5 g/L from raw glycerol. The 2,3-butanediol yield respect to the theoretical maximum yield was also improved through the fed-batch operation (90%). To date, this concentration is the highest produced amount employing as biocatalyst a non-pathogenic bacterium (level 1).

Catalytic Processes from Biomass-Derived Hexoses and Pentoses: A Recent Literature Overview

Biomass is a plentiful renewable source of energy, food, feed and chemicals. It fixes about 1–2% of the solar energy received by the Earth through photosynthesis in both terrestrial and aquatic plants like macro- and microalgae. As fossil resources deplete, biomass appears a good complement and eventually a good substitute feedstock, but still needs the development of relatively new catalytic processes. For this purpose, catalytic transformations, whether alone or combined with thermal ones and separation operations, have been under study in recent years. Catalytic biorefineries are based on dehydration-hydrations, hydrogenations, oxidations, epimerizations, isomerizations, aldol condensations and other reactions to obtain a plethora of chemicals, including alcohols, ketones, furans and acids, as well as materials such as polycarbonates. Nevertheless, there is still a need for higher selectivity, stability, and regenerability of catalysts and of process intensification by a wise combination of operations, either in-series or combined (one-pot), to reach economic feasibility. Here we present a literature survey of the latest developments for obtaining value-added products using hexoses and pentoses derived from lignocellulosic material, as well as algae as a source of carbohydrates for subsequent transformations.

Hydrolysis of Lipid-Extracted Chlorella vulgaris by Simultaneous Use of Solid and Liquid Acids

Microalgal biomass was hydrolyzed using a solid acid catalyst with the aid of liquid acid. The use of solid acid as the main catalyst instead of liquid acid was to omit subsequent neutralization and/or desalination steps, which are commonly required in using the resulting hydrolysates for microbial fermentation. The hydrolysis of 10 g/L of lipid-extracted Chlorella vulgaris containing 12.2% carbohydrates using 7.6 g/L Amberlyst 36 and 0.0075 N nitric acid at 150°C resulted in 1.08 g/L of mono-sugars with a yield of 88.5%. For hydrolysis of higher concentrations of the biomass over 10 g/L, the amount of Amberlyst 36 needed to be increased in proportion to the biomass concentration to maintain similar levels of hydrolysis performance. Increasing the solid acid concentration protected the surface of the solid acid from being severely covered by cell debris during the reaction. A hydrolysate of lipid-extracted C. vulgaris 50 g/L was used, with no post-treatment of desalination, for the cultivation of Klebsiella oxytoca producing 2,3-butanediol. Cell growth in the hydrolysate was found to be almost the same as in the conventional medium with the same monosaccharide composition, confirming its fermentation compatibility. It was noticeable that the yield of 2,3-butanediol with the hydrolysate was observed to be 2.6 times higher than that with the conventional medium. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2729, 2019.

Continuous-mode separation of fucose and 2,3-butanediol using a three-zone simulated moving bed process and its performance improvement by using partial extract-collection, partial extract-recycle, and partial desorbent-port closing

If a multi-component monosugar mixture including fucose was used as the substrates for the Klebsiella oxytoca fermentation, it could offer the following two benefits simultaneously; (i) the removal of all monosugars other than fucose, and (ii) the acquisition of 2,3-butanediol (BD). To utilize such two benefits in favor of the economical efficiency of the fucose production process, it is essential to accomplish a high-purity separation between fucose and BD on the basis of a highly-economical mode. To address this issue, we aimed to develop a simulated moving bed (SMB) process for continuous-mode separation of fucose and BD with high purities. It was first found that an Amberchrom-CG71C resin could become a suitable adsorbent for the separation of interest. The intrinsic parameters of fucose and BD on such proven adsorbent were determined, and then applied to the optimal design of the fucose-BD separation SMB. The capability of the designed SMB in ensuring high purities and high yields was experimentally verified. Finally, we devised two potential strategies to make a further improvement in product concentrations and/or desorbent usage while keeping the purities and yields of fucose and BD almost unchanged. The first strategy was based on partial extract-collection and partial extract-discard, which was found to result in 33% higher BD product concentration. The second strategy was based on partial extract-collection, partial extract-recycle, and partial desorbent-port closing, which could lead to 25% lower desorbent usage, 33% higher BD product concentration, and 7% higher fucose product concentration.

Inhibitory effect of high phenol concentration in treating coal gasification wastewater in anaerobic biofilter

In this paper, the inhibition of methanogens by phenol in coal gasification wastewater (CGW) was investigated by both anaerobic toxicity tests and a lab-scale anaerobic biofilter reactor (AF). The anaerobic toxicity tests indicated that keeping the phenol concentration in the influent under 280mg/L could maintain the methanogenic activity. In the AF treating CGW, the result showed that adding glucose solution as co-substrate could be beneficial for the quick start-up of the reactor. The effluent chemical oxygen demand (COD) and total phenol reached 1200 and 100mg/L, respectively, and the methane production rate was 175mLCH₄/gCOD/day. However, if the concentration of phenol was increased, the inhibition of anaerobic micro-organisms was irreversible. The threshold of total phenol for AF operation was 200-250mg/L. The extracellular polymeric substances (EPS) and particle size distribution of anaerobic granular sludge in the different stages were also examined, and the results indicated that the influence of toxicity in the system was more serious than its effect on flocculation of EPS. Moreover, the proportion of small size anaerobic granular sludge gradually increased from 10.2% to 34.6%. The results of high through-put sequencing indicated that the abundance of the Chloroflexi and Planctomycetes was inhibited by the toxicity of the CGW, and some shifts in the microbial community were observed at different stages.

Engineering of Klebsiella oxytoca for production of 2,3-butanediol via simultaneous utilization of sugars from a Golenkinia sp. hydrolysate

The Klebsiella oxytoca was engineered to produce 2,3-butanediol (2,3-BDO) simultaneously utilizing glucose and galactose obtained from a Golenkinia sp. hydrolysate. For efficient uptake of galactose at a high concentration of glucose, Escherichia coli galactose permease (GalP) was introduced, and the expression of galP under a weak-strength promoter resulted in simultaneous consumption of galactose and glucose. Next, to improve the sugar consumption, a gene encoding methylglyoxal synthase (MgsA) known as an inhibitor of multisugar metabolism was deleted, and the mgsA-null mutant showed much faster consumption of both sugars than the wild-type strain did. Finally, we demonstrated that the engineered K. oxytoca could utilize sugar extracts from a Golenkinia sp. hydrolysate and successfully produces 2,3-BDO.