1,3-Propanediol production by Klebsiella oxytoca NRRL-B199 from glycerol. Medium composition and operational conditions

An efficient production of bio-succinate in a novel metabolically engineered Klebsiella oxytoca by rational metabolic engineering and evolutionary adaptation

Klebsiella oxytoca KC004 (ΔadhEΔpta-ackAΔldhAΔbudABΔpflB) was engineered to enhance succinate production. The strain exhibited poor growth without succinate production due to its deficiencies in ATP production and NADH reoxidation. To overcome obstacles, evolutionary adaptation with over 6,000 generations of growth-based selection was conducted. Under anaerobic conditions, enhanced productions of ATP for growth and succinate for NADH reoxidation by the evolved KC004-TF160 strain were coupled to an increased transcript of PEP carboxykinase (pck) while those of genes in the oxidative branch of TCA cycle (gltA, acnAB, and icd), and pyruvate and acetate metabolisms (pykA, acs, poxB and tdcD) were alleviated. The expression of pyruvate dehydrogenase repressor (pdhR) decreased whereas threonine decarboxylase (tdcE) increased. KC004-TF160 produced succinate at 84 g/L (0.84 g/g, 79 % theoretical maximum). KC004-TF160 produced succinate at 0.87 g/g non-pretreated sugarcane molasses without addition of nutrients and buffers. KC004-TF160 may be a microbial platform for commercial production of bio-succinate.

Monitoring steady production of 1,3-propanediol during bioprospecting of glycerol-assimilating soil microbiome using dye-based pH-stat method

AIM

In this investigation, a dye-based pH-stat method was devised for monitoring steady production of 1,3-propanediol (1,3-PDO) during bioprospecting of glycerol-assimilating soil microbiome.

METHODS AND RESULTS

Soil samples were collected from two potential sites of CSIR-IIP, India. Selective enrichment of microbial consortia was done using the glycerol-based medium at initial stage, followed by purification to isolated colonies, after positive high-performance liquid chromatography detection of 1,3-PDO in the fermentation broth. When the purified isolated were re-tested for 1,3-PDO production, only two isolates namely Isolate 1 and Isolate 3 were capable of producing the targeted product preferably under anaerobic conditions. Based on better 1,3-PDO fermentation efficiency (Isolate 3, 22% vs Isolate 1, 4·48%) and acetic acid as the only major by-product, Isolate 3 was shortlisted for further studies. A dye-based technique was devised in which bromothymol blue was incorporated into the medium to monitor the pH drop due to acetic acid formation and hence change in colour. Visual change in colour helped in intermittent pH restoration. During fermentation, with pH stat being 8-8·5, Isolate 3 at 32°C yielded 0·67 mol mol^-1 1,3-PDO within a short span of 12 h only with an initial concentration of glycerol being 20 g l^-1 . Phylogenetic analysis revealed that Isolate 3 shared 95·8% homology with Citrobacter freundii CFNIH1 and hence designated as C. freundii IIP DR3.

CONCLUSION

This study demonstrated that during bioprospecting glycerol-assimilating microbiome, dye-based technique can be successfully employed. This technique can further be exploited to monitor consistent production of all microbial secondary metabolites that accompanies acid production.

SIGNIFICANCE AND IMPACT OF THE STUDY

Incorporation of 'Bromothymol blue' can visually help in the identification of pH drop in the medium, so that pH stat can be easily maintained during 1,3-PDO production from glycerol especially under shake flask conditions.

In silico prospection of microorganisms to produce polyhydroxyalkanoate from whey: Caulobacter segnis DSM 29236 as a suitable industrial strain

Polyhydroxyalkanoates (PHAs) are polyesters of microbial origin that can be synthesized by prokaryotes from noble sugars or lipids and from complex renewable substrates. They are an attractive alternative to conventional plastics because they are biodegradable and can be produced from renewable resources, such as the surplus of whey from dairy companies. After an in silico screening to search for ß-galactosidase and PHA polymerase genes, several bacteria were identified as potential PHA producers from whey based on their ability to hydrolyse lactose. Among them, Caulobacter segnis DSM 29236 was selected as a suitable strain to develop a process for whey surplus valorization. This microorganism accumulated 31.5% of cell dry weight (CDW) of poly(3-hydroxybutyrate) (PHB) with a titre of 1.5 g l-1 in batch assays. Moreover, the strain accumulated 37% of CDW of PHB and 9.3 g l-1 in fed-batch mode of operation. This study reveals this species as a PHA producer and experimentally validates the in silico bioprospecting strategy for selecting microorganisms for waste re-valorization.

Improved Raoultella planticola Strains for the Production of 2,3-Butanediol from Glycerol

Raw glycerol is an industrial byproduct from biodiesel production and is one of the most promising substrates for 2,3-butanediol (2,3-BD) production; however, 2,3-BD is not yet produced by fermentation from glycerol on a commercial scale due to poor process economics. Class 1 microorganism collections were screened and Raoultella planticola strain CECT 843 proved to be the best 2,3-BD producer, achieving (23.3 ± 1.4) g 2,3-BD per L and a yield of 36% (g 2,3-BD per g glycerol). To further increase product concentration and yield, R. planticola CEC T843 was subjected to random mutagenesis using ultra-violet (UV) light and ethyl methane sulfonate (EMS). Two mutant strains were found to produce at least 30% more 2,3-BD than the wild type: R. planticola IA1 [(30.8 ± 3.9) g 2,3-BD per L and 49% yield] and R. planticola IIIA3 [(30.5 ± 0.4) g 2,3-BD per L and 49% yield].

Optimization of the Enzymatic Saccharification Process of Milled Orange Wastes

Orange juice production generates a very high quantity of residues (Orange Peel Waste or OPW-50–60% of total weight) that can be used for cattle feed as well as feedstock for the extraction or production of essential oils, pectin and nutraceutics and several monosaccharides by saccharification, inversion and enzyme-aided extraction. As in all solid wastes, simple pretreatments can enhance these processes. In this study, hydrothermal pretreatments and knife milling have been analyzed with enzyme saccharification at different dry solid contents as the selection test: simple knife milling seemed more appropriate, as no added pretreatment resulted in better final glucose yields. A Taguchi optimization study on dry solid to liquid content and the composition of the enzymatic cocktail was undertaken. The amounts of enzymatic preparations were set to reduce their impact on the economy of the process; however, as expected, the highest amounts resulted in the best yields to glucose and other monomers. Interestingly, the highest content in solid to liquid (11.5% on dry basis) rendered the best yields. Additionally, in search for process economy with high yields, operational conditions were set: medium amounts of hemicellulases, polygalacturonases and β-glucosidases. Finally, a fractal kinetic modelling of results for all products from the saccharification process indicated very high activities resulting in the liberation of glucose, fructose and xylose, and very low activities to arabinose and galactose. High activity on pectin was also observed, but, for all monomers liberated initially at a fast rate, high hindrances appeared during the saccharification process.

1,3-Propanediol production from glycerol with a novel biocatalyst Shimwellia blattae ATCC 33430: Operational conditions and kinetics in batch cultivations

Shimwellia blattae ATCC 33430 as biocatalyst in the conversion of 1,3-propanediol from glycerol is herein evaluated. Several operational conditions in batch cultivations, employing pure and raw glycerol as sole carbon source, were studied. Temperature was studied at shaken bottle scale, while pH control strategy, together with the influence of raw glycerol and its impurities during fermentation were studied employing a 2L STBR. Thereafter, fluid dynamic conditions were considered by changing the stirring speed and the gas supply (air or nitrogen) in the same scale-up experiments. The best results were obtained at a temperature of 37°C, an agitation rate of 200rpm, with free pH evolution from 6.9 and subsequent control at 6.5 and no gas supply during the fermentation, employing an initial concentration of 30g/L of raw glycerol. Under these conditions, the biocatalyst is competitive, leading to results in line with other previous works in the literature in batch conditions, reaching a final concentration of 1,3-propanediol of 13.84g/L, with a yield of 0.45g/g and a productivity of 1.19g/(Lh) from raw glycerol.

Debottlenecking product inhibition in 1,3-propanediol fermentation by In-Situ Product Recovery

The present work describes the application of liquid-liquid extraction as an In-Situ product recovery (ISPR) technique to overcome the problem of product inhibition in 1,3-PD fermentation. As a part of initial screening experiments, six solvents were subjected to phase separation and biocompatibility tests to find the best extractant for in-situ removal of 1,3-PD from the bioreactor. These included tributylphosphate, ethyl acetate, butyl acetate, oleyl alcohol, oleic acid and hexanol. Of these, ethyl acetate was found to be the most suitable solvent for 1,3-PD extraction. Use of the selected extractant in continuous integrated fermentation-extraction was established by batch and fed-batch extractive fermentations which demonstrated a significantly improved 1,3-PD production of 35g/L and 74.5g/L, respectively. A steady state 1,3-PD concentration of 58g/L was obtained in continuous extractive system. Continuous cultivation with in-situ cell retention and in-situ 1,3-PD removal demonstrated a 5-fold enhancement in 1,3-PD productivity over non-extractive batch.