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Utilization of excess glycerol supplies derived from the burgeoning biodiesel industry has recently become very important. Glyceric acid (GA) is one of the most promising glycerol derivatives, and it is abundantly obtained from glycerol by a bioprocess using acetic acid bacteria. In this study, a novel branched-type poly(lactic acid) (PLA) was synthesized by polycondensation of lactide in the presence of GA. The resulting branched PLA had lower crystallinity and glass transition temperatures than the conventional linear PLA, and the peak associated with the melting point of the branched PLA disappeared. Moreover, in a blend of the branched polymer, the crystallization of the linear PLA occurred at a lower temperature. Thus, the branched PLA containing GA synthesized in this study could potentially be used as a novel bio-based modifier for PLA.

To prevent dihydroxyacetone (DHA) by-production during glyceric acid (GA) production from glycerol using Gluconobacter frateurii, we used a G. frateurii THD32 mutant, ΔsldA, in which the glycerol dehydrogenase subunit-encoding gene (sldA) was disrupted, but ΔsldA grew much more slowly than the wild type, growth starting after a lag of 3 d under the same culture conditions. The addition of 1% w/v D-sorbitol to the medium improved both the growth and the GA productivity of the mutant, and ΔsldA produced 89.1 g/l GA during 4 d of incubation without DHA accumulation.

Dihydroxyacetone (DHA) production from glycerol by Gluconobacter oxydans is an industrial form of fermentation, but some problems exist related to microbial DHA production. For example, glycerol inhibits DHA production and affects its biological activity. G. oxydans produces both DHA and glyceric acid (GA) from glycerol simultaneously, and membrane-bound glycerol dehydrogenase and membrane-bound alcohol dehydrogenases are involved in the two reactions, respectively. We discovered that the G. oxydans mutant DeltaadhA, in which the membrane-bound alcohol dehydrogenase-encoding gene (adhA) was disrupted, significantly improved its ability to grow in a higher concentration of glycerol and to produce DHA compared to a wild-type strain. DeltaadhA grew on 220 g/l of initial glycerol and produced 125 g/l of DHA during a 3-d incubation, whereas the wild-type did not. Resting DeltaadhA cells converted 230 g/l of glycerol aqueous solution to 139.7 g/l of DHA during a 3-d incubation. The inhibitory effect of glycerate sodium salt on DeltaadhA was investigated. An increase in the glycerate concentration at the beginning of growth resulted in decreases in both growth and DHA production.

Glyceric acid (GA), an unfamiliar biotechnological product, is currently produced as a small by-product of dihydroxyacetone production from glycerol by Gluconobacter oxydans. We developed a method for the efficient biotechnological production of GA as a target compound for new surplus glycerol applications in the biodiesel and oleochemical industries. We investigated the ability of 162 acetic acid bacterial strains to produce GA from glycerol and found that the patterns of productivity and enantiomeric GA compositions obtained from several strains differed significantly. The growth parameters of two different strain types, Gluconobacter frateurii NBRC103465 and Acetobacter tropicalis NBRC16470, were optimized using a jar fermentor. G. frateurii accumulated 136.5 g/liter of GA with a 72% d-GA enantiomeric excess (ee) in the culture broth, whereas A. tropicalis produced 101.8 g/liter of d-GA with a 99% ee. The 136.5 g/liter of glycerate in the culture broth was concentrated to 236.5 g/liter by desalting electrodialysis during the 140-min operating time, and then, from 50 ml of the concentrated solution, 9.35 g of GA calcium salt was obtained by crystallization. Gene disruption analysis using G. oxydans IFO12528 revealed that the membrane-bound alcohol dehydrogenase (mADH)-encoding gene (adhA) is required for GA production, and purified mADH from G. oxydans IFO12528 catalyzed the oxidation of glycerol. These results strongly suggest that mADH is involved in GA production by acetic acid bacteria. We propose that GA is potentially mass producible from glycerol feedstock by a biotechnological process.

Gluconobacter sp. NBRC3259 converted glycerol to glyceric acid (GA). The enantiomeric composition of the GA produced was a mixture of DL-forms with a 77% enantiomeric excess of D-GA. After culture conditions, such as initial glycerol concentration, types and amounts of nitrogen sources, and initial pH, were optimized, Gluconobacter sp. NBRC3259 produced 54.7 g/l of GA as well as 33.7 g/l of dihydroxyacetone (DHA) from 167 g/l of glycerol during 4 d of incubation in a jar fermentor with pH control. GA production from raw glycerol samples, the main by-product of the transesterification process in the biodiesel production and oleochemical industries, was also evaluated after proper pretreatment of the samples. Using a raw glycerol sample with activated charcoal pretreatment, 45.9 g/l of GA and 28.2 g/l of DHA were produced from 174 g/l of glycerol.

A yeast strain, 25N-2B, that produces D-arabitol from glycerol, was identified as Candida parapsilosis based on phylogenetic, morphological, physiological, and biochemical analyses. It produced 32.2 g/L D-arabitol from 170 g/L glycerol in a jar fermentor. The D-arabitol in the reaction mixture was then completely converted to D-xylulose using Gluconobacter oxydans NBRC3293. The product was isolated from the reaction mixture and confirmed to be D-xylulose by (1)H and (13)C-NMR and optical rotation.

Bacterial strains capable of converting glycerol to glyceric acid (GA) were screened among the genera Acetobacter and Gluconacetobacter. Most of the tested Acetobacter and Gluconacetobacter strains could produce 1.8 to 9.3 g/l GA from 10% (v/v) glycerol when intact cells were used as the enzyme source. Acetobacter tropicalis NBRC16470 was the best GA producer and was therefore further investigated. Based on the results of high-performance liquid chromatography analysis and specific rotation, the enantiomeric composition of the produced GA was D-glyceric acid (D-GA). The productivity of D-GA was enhanced with the addition of both 15% (v/v) glycerol and 20 g/l yeast extract. Under these optimized conditions, A. tropicalis NBRC16470 produced 22.7 g/l D-GA from 200 g/l glycerol during 4 days of incubation in a jar fermentor.

Thirty-five glycerol-assimilating bacteria have recently been isolated from soil samples. Amplified ribosomal DNA restriction analysis revealed that these strains are grouped into four genetically different types of bacteria. Gas chromatography-mass spectrometry analysis of glycerol metabolites produced by the three selected strains (strains HH7, HH12, and HH31) revealed that extracts of culture liquid with ethyl acetate contains acetyl monoglyceride (monoacetin), which has not previously been reported as a glycerol metabolite and is used as a solvent, plasticizer, and food additive, as well as for other industrial purposes. The sequence analyses of the 16S rRNA genes from the selected strains showed that all of them belong to the Enterobacteriaceae.

In this paper, thermotolerant fungal strains which can grow on glycerol as the sole carbon source were isolated from soil samples. Morphological and molecular phylogenetic analyses of ten isolated strains showed that all strains belong to Aspergillus fumigatus. Analysis of their cellular fatty acid composition revealed that all the strains accumulated lignoceric acid (C24:0), suggesting that the isolated strains can be used to produce this high-value long-chain fatty acid from glycerol.