Effect of composites based nickel foam anode in microbial fuel cell using Acetobacter aceti and Gluconobacter roseus as a biocatalysts.

This study explores the use of materials such as chitosan (chit), polyaniline (PANI) and titanium carbide (TC) as anode materials for microbial fuel cells. Nickel foam (NF) was used as the base anode substrate. Four different types of anodes (NF, NF/PANI, NF/PANI/TC, NF/PANI/TC/Chit) are thus prepared and used in batch type microbial fuel cells operated with a mixed consortium of Acetobacter aceti and Gluconobacter roseus as the biocatalysts and bad wine as a feedstock. A maximum power density of 18.8Wm(-3) (≈2.3 times higher than NF) was obtained in the case of the anode modified with a composite of PANI/TC/Chit. The MFCs running under a constant external resistance of (50Ω) yielded 14.7% coulombic efficiency with a maximum chemical oxygen demand (COD) removal of 87-93%. The overall results suggest that the catalytic materials embedded in the chitosan matrix show the best performance and have potentials for further development.

Chemical mutagenesis of Gluconobacter frateurii to construct methanol-resistant mutants showing glyceric acid production from methanol-containing glycerol.

To produce glyceric acid (GA) from methanol-containing glycerol, resistance to methanol of Gluconobacter frateurii NBRC103465 was improved by chemical mutagenesis using N-methyl-N'-nitro-N-nitrosoguanidine. The obtained mutant Gf398 produced 6.3 g/L GA in 5% (v/v) methanol-containing 17% (w/v) glycerol medium, in which the wild-type strain neither grew nor produced GA.

First report of endocarditis by Gluconobacter spp. in a patient with a history of intravenous-drug abuse.

Gluconobacter belongs to the acetic acid bacteria (AAB), which are microorganisms commonly found in the environment and used in the food industry. These bacteria have increasingly been reported as organisms that can potentially infect humans. We report a case of Gluconobacter spp. bloodstream infection associated with endocardial lesions in a 25 year-old female intravenous drug abuser. To the best of our knowledge, this is the first case of Gluconobacter spp. endocarditis reported in the literature. For the first time we report that a multiresistant strain belonging to the genus Gluconobacter can cause endocarditis, giving evidence to the fact that this microorganism should be considered a new opportunistic human pathogen.

Production of glyceric acid by Gluconobacter sp. NBRC3259 using raw glycerol.

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.

Purification and properties of two different dihydroxyacetone reductases in Gluconobacter suboxydans grown on glycerol.

It is well known that in oxidative fermentation microbial growth is improved by the addition of glycerol. In a wild strain, glycerol was converted rapidly to dihydroxyacetone (DHA) quantitatively in the early growth phase by the action of quinoprotein glycerol dehydrogenase (GLDH), and then DHA was incorporated into the cells by the early stationary phase. Two DHA reductases (DHARs), NADH-dependent (NADH-DHAR) (EC 1.1.1.6) and NADPH-dependent (NADPH-DHAR) (EC 1.1.1.156), were detected in the same cytoplasm of Gluconobacter suboxydans IFO 3255. The former appeared to be inducible and labile in nature while the latter was constitutive and stable. The two DHARs were separated each other and were finally purified to crystalline enzymes. This report might be the first one dealing with NADPH-DHAR that has been crystallized. The two DHARs were specific only to DHA reduction to glycerol and thus contributed to cytoplasmic DHA metabolism, resulting in an improved biomass yield with the addition of glycerol.

Effect of glycine betaine on osmoadaptation of Propionibacterium acidipropionici cultivated in elevated osmolarities.

The sensitivity of industrial strains Acetobacter aceti, Gluconobacter frateurii, and Propionibacterium acidipropionici to osmotic stress was studied. Growth of A. aceti and G. frateurii was totally inhibited at 0.4 M NaCl concentration, but P. acidipropionici was able to grow on a medium containing 1.2 M NaCl. Addition of glycine betaine to the medium had no detectable osmoprotective effect on A. aceti and G. frateurii cultivations in elevated NaCl concentrations, but it enabled cells of P. acidipropionici to achieve faster the maximum specific growth rate after the prolonged lag phase and therefore to gain faster the final biomass and product concentrations. The final concentrations of biomass and product of P. acidipropionici were the same as for the cultivations of the bacterium without NaCl and glycine betaine present in the medium. Intracellular accumulation of glycine betaine was detected in P. acidipropionici cells cultivated in the medium containing glycine betaine. The amount accumulated increased with NaCl concentration, suggesting that glycine betaine plays an important role in the osmoadaptation.

Bacterial response to acetate challenge: a comparison of tolerance among species.

Although acetate formation and tolerance are important criteria for various aspects of biotechnological process development, available studies on acetate tolerance in different species are disparate. We evaluate the response of eight bacterial strains, including two variants of Escherichia coli, two variants of Staphylococcus capitis, and one each of Acetobacter aceti, Gluconobacter suboxydans, Lactobacillus acetotolerans, and L. bulgaricus, to acetate challenges under identical conditions. Our findings were: (1) wild-type organisms of species that are considered tolerant of acetate perform only slightly better than E. coli in unadapted shaker cultures; (2) the ability to tolerate acetate is strongly dependent on the carbon source, and is, especially for E. coli, much greater on glycerol than on glucose; (3) respiration is not as important to acetate tolerance in E. coli and S. capitis as has been reported for the acetic acid bacteria; (4) S. capitis was the least affected by acetate under all conditions and grew at up to 44 g/l acetate without any preconditioning; and (5) qualitative high-throughput screening of growth characteristics can be achieved with relatively inexpensive multiwell plate readers.