Production of dihydroxyacetone from an aqueous solution of glycerol in the reaction catalyzed by an immobilized cell preparation of acetic acid bacteria Gluconobacter oxydans ATCC 621

High-Yield Production of Dihydroxyacetone from Crude Glycerol in Fed-Batch Cultures of Gluconobacter oxydans

The strain Gluconobacter oxydans LMG 1385 was used for the bioconversion of crude glycerol to dihydroxyacetone. The suitability of fed-batch cultures for the production of dihydroxyacetone was determined, and the influence of the pH of the culture medium and the initial concentration of glycerol on maximizing the concentration of dihydroxyacetone and on the yield and speed of obtaining dihydroxyacetone by bioconversion was examined. The feeding strategy of the substrate (crude glycerol) during the process was based on measuring the dissolved oxygen tension of the culture medium. The highest concentration of dihydroxyacetone PK = 175.8 g·L-1 and the highest yield YP/Sw = 94.3% were obtained when the initial concentration of crude glycerol was S0 = 70.0 g·L-1 and the pH of the substrate was maintained during the process at level 5.0.

Continuous catalytic production of 1,3-dihydroxyacetone: Sustainable approach combining perfusion cultures and immobilized cells

Currently, the predominant method for the industrial production of 1,3-dihydroxyacetone (DHA) from glycerol involves fed-batch fermentation. However, previous research has revealed that in the biocatalytic synthesis of DHA from glycerol, when the DHA concentration exceeded 50 g·L-1, it significantly inhibited microbial growth and metabolism, posing a challenge in maintaining prolonged and efficient catalytic production of DHA. In this study, a new integrated continuous production and synchronous separation (ICSS) system was constructed using hollow fiber columns and perfusion culture technology. Additionally, a cell reactivation technique was implemented to extend the biocatalytic ability of cells. Compared with fed-batch fermentation, the ICSS system operated for 360 h, yielding a total DHA of 1237.8 ± 15.8 g. The glycerol conversion rate reached 97.7 %, with a productivity of 3.44 g·L-1·h-1, representing 485.0 % increase in DHA production. ICSS system exhibited strong operational characteristics and excellent performance, indicating significant potential for applications in industrial bioprocesses.

New perspectives into Gluconobacter-catalysed biotransformations

Different from other aerobic microorganisms that oxidise carbon sources to water and carbon dioxide, Gluconobacter catalyses the incomplete oxidation of various substrates with regio- and stereoselectivity. This ability, as well as its capacity to release the resulting products into the reaction media, place Gluconobacter as a privileged member of a non-model microorganism class that may boost industrial biotechnology. Knowledge of new technologies applied to Gluconobacter has been piling up in recent years. Advancements in its genetic modification, application of immobilisation tools and careful designs of the transformations, have improved productivities and stabilities of Gluconobacter strains or enabled new bioconversions for the production of valuable marketable chemicals. In this work, the latest advancements applied to Gluconobacter-catalysed biotransformations are summarised with a special focus on recent available tools to improve them. From genetic and metabolic engineering to bioreactor design, the most recent works on the topic are analysed in depth to provide a comprehensive resource not only for scientists and technologists working on/with Gluconobacter, but for the general biotechnologist.

The industrial versatility of Gluconobacter oxydans: current applications and future perspectives

Gluconobacter oxydans is a well-known acetic acid bacterium that has long been applied in the biotechnological industry. Its extraordinary capacity to oxidize a variety of sugars, polyols, and alcohols into acids, aldehydes, and ketones is advantageous for the production of valuable compounds. Relevant G. oxydans industrial applications are in the manufacture of L-ascorbic acid (vitamin C), miglitol, gluconic acid and its derivatives, and dihydroxyacetone. Increasing efforts on improving these processes have been made in the last few years, especially by applying metabolic engineering. Thereby, a series of genes have been targeted to construct powerful recombinant strains to be used in optimized fermentation. Furthermore, low-cost feedstocks, mostly agro-industrial wastes or byproducts, have been investigated, to reduce processing costs and improve the sustainability of G. oxydans bioprocess. Nonetheless, further research is required mainly to make these raw materials feasible at the industrial scale. The current shortage of suitable genetic tools for metabolic engineering modifications in G. oxydans is another challenge to be overcome. This paper aims to give an overview of the most relevant industrial G. oxydans processes and the current strategies developed for their improvement.

Dihydroxyacetone production via heterogeneous biotransformations of crude glycerol

In this work, several immobilization strategies for Gluconobacter oxydans NBRC 14819 (Gox) were tested in the bioconversion of crude glycerol to dihydroxyacetone (DHA). Agar, agarose and polyacrylamide were evaluated as immobilization matrixes. Glutaraldehyde crosslinked versions of the agar and agarose preparations were also tested. Agar immobilized Gox proved to be the best heterogeneous biocatalyst in the bioconversion of crude glycerol reaching a quantitative production of 50 g/L glycerol into DHA solely in water. Immobilization allowed reutilization for at least eight cycles, reaching four times more DHA than the amount obtained by a single batch of free cells which cannot be reutilized. An increase in scale of 34 times had no impact on DHA productivity. The results obtained herein constitute a contribution to the microbiological production of DHA as they not only attain unprecedented productivities for the reaction with immobilized biocatalysts but also proved that it is feasible to do it in a clean background of solely water that alleviates the cost of downstream processing.

Metabolomic and kinetic investigations on the electricity-aided production of butanol by Clostridium pasteurianum strains

In this contribution, we studied the effect of electro-fermentation on the butanol production of Clostridium pasteurianum strains by a targeted metabolomics approach. Two strains were examined: an electrocompetent wild type strain (R525) and a mutant strain (dhaB mutant) lacking formation of 1,3-propanediol (PDO). The dhaB-negative strain was able to grow on glycerol without formation of PDO, but displayed a high initial intracellular NADH/NAD ratio which was lowered subsequently by upregulation of the butanol production pathway. Both strains showed a 3-5 fold increase of the intracellular NADH/NAD ratio when exposed to cathodic current in a bioelectrochemical system (BES). This drove an activation of the butanol pathway and resulted in a higher molar butanol to PDO ratio for the R525 strain. Nonetheless, macroscopic electron balances suggest that no significant amount of electrons derived from the BES was harvested by the cells. Overall, this work points out that electro-fermentation can be used to trigger metabolic pathways and improve product formation, even when the used microbe cannot be considered electroactive. Accordingly, further studies are required to unveil the underlying (regulatory) mechanisms.

Photocatalytic production of dihydroxyacetone from glycerol on TiO2 in acetonitrile

In this paper, photocatalytic production of dihydroxyacetone (DHA) from glycerol in acetonitrile on TiO₂ was investigated. HPLC-MS analysis showed that glycerol was converted to DHA, glyceraldehyde (GAD), glyceric acid and several other chemicals. Using acetonitrile as the reaction medium instead of water not only provided a more selective process for production of DHA but also increased the glycerol conversion. After 300 min, with 1 g L⁻¹ catalyst loading and 4 mM initial glycerol concentration, glycerol conversion and DHA selectivity were 96.8% and 17.8% in acetonitrile compared to 36.1% and 14.7% in water, respectively. The half-life of glycerol decreased by a factor of 6.2, from 467 min to 75 min, by changing the solvent from water to acetonitrile. Experiments using biodiesel-derived crude glycerol verified the effectiveness of the proposed process for the photocatalytic production of DHA from crude glycerol. A mechanism was proposed to explain the higher selectivity towards DHA over GAD in this process.

Photocatalytic conversion of glycerol and selectivity for dihydroxyacetone production was increased by using acetonitrile as the reaction medium.

Modeling of Osmotic Dehydration of Apples in Sugar Alcohols and Dihydroxyacetone (DHA) Solutions

The purpose of this paper is twofold: on the one hand, we verify effectiveness of alternatives solutes to sucrose solution as osmotic agents, while on the other hand we intend to analyze modeling transfer parameters, using different models. There has also been proposed a new mass transfer parameter-true water loss, which includes actual solid gain during the process. Additional consideration of a new ratio (Cichowska et al. Ratio) can be useful for better interpretation of osmotic dehydration (OD) in terms of practical applications. Apples v. Elise were dipped into 30% concentrated solutions of erythritol, xylitol, maltitol, and dihydroxyacetone (DHA) to remove some water from the tissue. To evaluate the efficiency of these solutes, 50% concentrated sucrose solution was used as a control. All of the tested osmotic agent, except maltitol, were effective in the process as evidenced by high values in the true water loss parameter. Solutions of erythritol and xylitol in 30% concentrate could be an alternative to sucrose in the process of osmotic dehydration. Peleg's, Kelvin⁻Voigt, and Burgers models could fit well with the experimental data. modeling of mass transfer parameters, using Peleg's model can be satisfactorily supplemented by Kelvin⁻Voigt and Burgers model for better prediction of OD within the particular periods of the process.

Valorization of Waste Glycerol to Dihydroxyacetone with Biocatalysts Obtained from Gluconobacter oxydans

Waste glycerol is the main by-product generated during biodiesel production, in an amount reaching up to 10% of the produced biofuel. Is there any method which allows changing this waste into industrial valuable compounds? This manuscript describes a method for valorization of crude glycerol via microbial bioconversion. It has been shown that the use of free and immobilized biocatalysts obtained from Gluconobacter oxydans can enable beneficial valorization of crude glycerol to industrially valuable dihydroxyacetone. The highest concentration of this compound, reaching over 20 g·L−1, was obtained after 72 h of biotransformation with free G. oxydans cells, in a medium containing 30 or 50 g·L−1 of waste glycerol. Using a free cell extract resulted in higher concentrations of dihydroxyacetone and a higher valorization efficiency (up to 98%) compared to the reaction with an immobilized cell extract. Increasing waste glycerol concentration to 50 g·L−1 causes neither a faster nor higher increase in product yield and reaction efficiency compared to its initial concentration of 30 g·L−1. The proposed method could be an alternative for utilization of a petrochemical waste into industry applicated chemicals.

Repeated biotransformation of glycerol to 1,3-dihydroxyacetone by immobilized cells of Gluconobacter oxydans with glycerol- and urea-feeding strategy in a bubble column bioreactor

Some inorganic nitrogen sources and amino acids instead of yeast extract, which resulted in trouble of product purification, were introduced for 1,3-dihydroxyacetone (DHA) production by biotransformation with Gluconobacter oxydans. The results showed that urea is an optimal nitrogen source. Furthermore, the effects of glycerol- and urea-feeding strategies for DHA production by immobilized cells in a home-made bubble column bioreactor were optimized. Cells immobilization was prepared by cultivation in the bioreactor packed with porous ceramics, and then the broth was removed. Then, repeated biotransformation by continuous-feeding of glycerol and urea was developed. Up to 96.4±4.1g/L of average DHA concentration with 94.8±2.2% of average conversion rate of glycerol to DHA was achieved after 12 cycles of run. Near colorless DHA solution with few impurities was obtained and the production cost could be decreased.