Modeling for gellan gum production by Sphingomonas paucimobilis ATCC 31461 in a simplified medium

Medium factor optimization and fermentation kinetics for phenazine-1-carboxylic acid production by Pseudomonas sp. M18G

We investigated the production of biofungicide phenazine-1-carboxlic (PCA) by Pseudomonas sp. M18G, a gacA-deficient mutant of M18 for PCA high-production. Glucose was chosen as the optimal carbon source and soy peptone as the nitrogen source. A Plackett-Burman design revealed that glucose, soy peptone and NaCl were the most significant factors in PCA fermentation. Response surface methodology (RSM) and artificial neural network (ANN) models involving the significant factors were developed using common data. The prediction accuracy of ANN was slightly higher compared to RSM. The genetic algorithm (GA) was used to search the optimal input space of the trained ANN model and find the corresponding PCA yield. The optimum composition was found to be: glucose 34.3 g L(-1), soy peptone 43.2 g L(-1), NaCl 5.7 g L(-1), and the predictive maximum PCA yield reached 980.1 microg mL(-1). The optimized medium allowed PCA yield to be increased from 673.3 to 966.7 microg mL(-1) after verification experiment tests. Additionally, PCA fermentation kinetics was investigated. Kinetic models based on the modified Logistic and Luedeking-Piret equations were developed, providing a good description of temporal variations of biomass (X), product (P), and substrate (S) in PCA fermentation.

Metabolic alternations in SOD-deficient Escherichia coli cells when cultivated under oxidative stress from photoexcited titanium dioxide

Superoxide dismutase (SOD)-deficient Escherichia coli was cultivated under the oxidative stress generated by photoexcited titanium dioxide. These cells showed higher growth rate and glucose consumption rate with accelerated accumulation of acetic acid in the medium, compared to the cells cultivated under the normal condition without the stress. Under the stress condition, the activity of acetate kinase and mRNA expressions of the enzymes for acetic acid production (pta and ackA) were approximately doubled, while the activity of citrate synthase and mRNA expressions of the enzymes in TCA cycle (gltA, acnA, icd, sucA, sucC, sdhA, fumA and mdh) were repressed by about half, as compared with those under the normal condition. These results suggest that the stress-suffering cells switch the metabolic pathway into a "suppressed aerobiosis", possibly for lowering the generation of reactive oxygen species.

Degradation of carbazole by microbial cells immobilized in magnetic gellan gum gel beads

Polycyclic aromatic heterocycles, such as carbazole, are environmental contaminants suspected of posing human health risks. In this study, we investigated the degradation of carbazole by immobilized Sphingomonas sp. strain XLDN2-5 cells. Four kinds of polymers were evaluated as immobilization supports for Sphingomonas sp. strain XLDN2-5. After comparison with agar, alginate, and kappa-carrageenan, gellan gum was selected as the optimal immobilization support. Furthermore, Fe(3)O(4) nanoparticles were prepared by a coprecipitation method, and the average particle size was about 20 nm with 49.65-electromagnetic-unit (emu) g(-1) saturation magnetization. When the mixture of gellan gel and the Fe(3)O(4) nanoparticles served as an immobilization support, the magnetically immobilized cells were prepared by an ionotropic method. The biodegradation experiments were carried out by employing free cells, nonmagnetically immobilized cells, and magnetically immobilized cells in aqueous phase. The results showed that the magnetically immobilized cells presented higher carbazole biodegradation activity than nonmagnetically immobilized cells and free cells. The highest biodegradation activity was obtained when the concentration of Fe(3)O(4) nanoparticles was 9 mg ml(-1) and the saturation magnetization of magnetically immobilized cells was 11.08 emu g(-1). Additionally, the recycling experiments demonstrated that the degradation activity of magnetically immobilized cells increased gradually during the eight recycles. These results support developing efficient biocatalysts using magnetically immobilized cells and provide a promising technique for improving biocatalysts used in the biodegradation of not only carbazole, but also other hazardous organic compounds.

Deproteinization of gellan gum produced by Sphingomonas paucimobilis ATCC 31461

Deproteinization is a technical bottleneck in the purification of viscous water-soluble polysaccharides. The aim of this work is to provide an appropriate approach to deproteinize crude gellan gum. Several methods of deproteinization were investigated, including Sevag method, alkaline protease, papain and neutral protease. The results revealed that Sevag method had high deproteinization efficiency (87.9%), but it showed dissatisfactory recovery efficiency of gellan gum (28.6%), which made it less advisable in industrial applications. The deproteinization by alkaline protease was demonstrated in this work for the first time, indicating alkaline protease was preferred in the deproteinization of crude gellan gum with high polysaccharide recovery (89.3%) and high deproteinization efficiency (86.4%).