Present state and perspective of downstream processing of biologically produced 1,3-propanediol and 2,3-butanediol

Liquid-liquid equilibria in solutions with potential ecological importance

In the last three years, our research follows two main issues, defined by the slogans: ?Green Meets Toxic? and ?Green Meets Green?. The first issue considers the potential use of ambient friendly solvents for toxic organic compounds of industrial and practical importance. The other is related to liquid phase behavior in solutions of ecologically sustainable substances. The ?Green? solvents studied are: ionic liquids, liquid poly(ethylene glycol), glycerol and 1,2 and 1,3-propanediol.

Biotechnological production of 2,3-butanediol--current state and prospects

Biotechnological production of 2,3-butanediol (hereafter referred to as 2,3-BD) from wastes and excessive biomass is a promising and attractive alternative for traditional chemical synthesis. In the face of scarcity of fossil fuel supplies the bio-based process is receiving a significant interest, since 2,3-BD may have multiple practical applications (e.g. production of synthetic rubber, plasticizers, fumigants, as an antifreeze agent, fuel additive, octane booster, and many others). Although the 2,3-BD pathway is well known, microorganisms able to ferment biomass to 2,3-BD have been isolated and described, and attempts of pilot scale production of this compound were made, still much has to be done in order to achieve desired profitability. This review summarizes hitherto gained knowledge and experience in biotechnological production of 2,3-BD, sources of biomass used, employed microorganisms both wild type and genetically improved strains, as well as operating conditions applied.

High production of 2,3-butanediol from glycerol by Klebsiella pneumoniae G31

The microbial production of high amounts of 2,3-butanediol (2,3-BD) from glycerol as a sole carbon source by the Bulgarian isolate Klebsiella pneumoniae G31 was studied in a series of fed-batch processes. The following conditions were evaluated as optimal: micro-aerobic cultivation in modified media, without pH control. Beginning at pH 8, 49.2 g/l of 2,3-BD was produced as negligible concentrations of by-products were received. The pH is the most important factor ruling the 2,3-BD production. Spontaneous pH changes and products formation in time were investigated, performing fermentations with non-controlled pH starting at different initial pH. In lack of external maintenance, the microorganism attempted to control the pH using acetate/2,3-BD alternations of the oxidative pathway of glycerol catabolism, which resulted in pH fluctuations. Thus, the culture secreted 2,3-BD at unequal portions, either allowing or detaining the acetate synthesis. More alkaline initial pH led to enhanced 2,3-BD accumulation as a response to the increased amplitudes of the pH variations. When the pH was maintained constant, the yield of 2,3-BD was very poor. These cultures remained viable only 72 h; whereas, the pH self-controlling cells lived and produced 2,3-BD up to 280 h. In conclusion, the formation of 2,3-BD is a result of an adaptive mechanism of pH self-control, responding to spontaneous pH drops during glycerol fermentation.

Elimination of by-product formation during production of 1,3-propanediol in Klebsiella pneumoniae by inactivation of glycerol oxidative pathway

The microbial production of 1,3-propanediol (1,3-PD) by Klebsiella pneumoniae involves the formation of various by-products, which are synthesized through the oxidative pathway. To eliminate the by-products synthesis, the oxidative branch of glycerol metabolism was inactivated by constructing two mutant strains. In one of the mutant strains, the structural genes encoding glycerol dehydrogenase and dihydroxyacetone kinase were deleted from the chromosomal DNA, whereas in the second mutant strain dhaR, which is a putative transcription factor that activates, gene expression was deleted from the chromosomal DNA. In the resultant mutant strains lacking the dhaT gene encoding 1,3-PD oxidoreductase, which was simultaneously deleted while replacing the native promoter with the lacZ promoter, the by-product formation except for acetate was eliminated, but it still produced 1,3-PD at a lower level, which might be due to a putative oxidoreductase that catalyzes the production of 1,3-PD. The recombinant strains in which the reductive pathway was recovered produced slightly lower amount of 1,3-PD as compared to the parent strain, which might be due to the reduced activity of DhaB caused by the substitution of the promoter. However, the production yield was higher in the recombinant strain (0.57 mol mol(-1)) than the wild type Cu strain (0.47 mol mol(-1)).

Adding value to renewables: a one pot process combining microbial cells and hydrogen transfer catalysis to utilise waste glycerol from biodiesel production

Waste glycerol was converted to secondary amines in a one pot reaction, using Clostridium butyricum and catalytic hydrogen transfer-mediated amination.

Methanol-based industrial biotechnology: current status and future perspectives of methylotrophic bacteria

Methanol is one of the building blocks in the chemical industry and can be synthesized either from petrochemical or renewable resources, such as biogas. Bioprocess technology with methylotrophic bacteria is well established, as illustrated by large-scale single-cell protein production in the past. During recent years, the first genomes of methylotrophs have been sequenced and significant progress in elucidating their metabolism has been made. In addition, the tool set for genetic engineering of methylotrophic bacteria has expanded greatly and strategies to produce fine and bulk chemicals with methylotrophs have been described. This review highlights the potential of these bacteria for the development of economically competitive bioprocesses based on methanol as an alternative carbon source, bringing together biological, technical and economic considerations.