Comparative investigation on a hexane-degrading strain with different cell surface hydrophobicities mediated by starch and chitosan.

Bioremediation usually exhibits low removal efficiency toward hexane because of poor water solubility, which limits the mass transfer rate between the substrate and microorganism. This work aimed to enhance the hexane degradation rate by increasing cell surface hydrophobicity (CSH) of the degrader, Pseudomonas mendocina NX-1. The CSH of P. mendocina NX-1 was manipulated by treatment with starch and chitosan solution of varied concentrations, reaching a maximum hydrophobicity of 52%. The biodegradation of hexane conformed to the Haldane inhibition model, and the maximum degradation rate (ν max) of the cells with 52% CSH was 0.72 mg (mg cell)-1·h-1 in comparison with 0.47 mg (mg cell)-1·h-1 for cells with 15% CSH. The production of CO2 by high CSH cells was threefold higher than that by cells at 15% CSH within 30 h, and the cumulative rates of O2 consumption were 0.16 and 0.05 mL/h, respectively. High CSH was related to low negative charge carried by the cell surface and probably reduced the repulsive electrostatic interactions between hexane and microorganisms. The FT-IR spectra of cell envelopes demonstrated that the methyl chain was inversely proportional to increasing CSH values, but proteins exhibited a positive effect to CSH enhancement. The ratio of extracellular proteins and polysaccharides increased from 0.87 to 3.78 when the cells were treated with starch and chitosan, indicating their possible roles in increased CSH.

Poly-3-hydroxyoctanoate P(3HO), a medium chain length polyhydroxyalkanoate homopolymer from Pseudomonas mendocina.

Pseudomonas mendocina was found to produce a unique homopolymer of poly(3-hydroxyoctanoate), P(3HO), rather than a copolymer, when grown on sodium octanoate as the sole carbon source. Although this polymer has been produced by other organisms, interestingly this is the first time an absolute homopolymer has been produced by a wild type organism. In addition, a detailed study on the effects of different extraction methods on the yield, molecular weight, thermal properties, and lipopolysaccharide content of P(3HO) has been carried out. The organism was able to accumulate P(3HO) up to 31.38% of its dry cell weight within 48 h in mineral salt medium. Characterization of the monomer was carried out using FTIR, GC-MS, (13)C, (1)H, and HSQC NMR spectroscopy. The polymer had a crystallinity of 37.5%, Young's modulus value of 11.6 MPa and contact angle of 77.3°. Microstructural studies of solvent cast polymer films revealed a smooth surface topography with a root-mean-square roughness value of 0.238 µm.

Simultaneous production and characterization of medium-chain-length polyhydroxyalkanoates and alginate oligosaccharides by Pseudomonas mendocina NK-01.

When Pseudomonas mendocina NK-01 was cultivated in a 200-L fermentor using glucose as carbon source, 0.316 g L(-1) medium-chain-length polyhydroxyalkanoate (PHA(MCL)) and 0.57 g L(-1) alginate oligosaccharides (AO) were obtained at the end of the process. GC/MS was used to characterize the PHA(MCL), which was found to be a polymer mainly consisting of 3HO (3-hydroxyoctanoate) and 3HD (3-hydroxydecanoate). T (m) and T (g) values for the PHA(MCL) were 51.03 °C and -41.21 °C, respectively, by DSC. Its decomposition temperature was about 300 °C. The elongation at break was 700% under 12 MPa stress. MS and GPC were also carried out to characterize the AO which had weight-average molecular weights of 1,546 and 1,029 Da, respectively, for the two main components at the end of the fermentation process. MS analysis revealed that the AO were consisted of ß-D-mannuronic acid and/or α-L-guluronic acid, and the ß-D-mannuronic acid and/or α-L-guluronic acid residues were partially acetylated at position C2 or C3.

Comparison of medium-chain-length polyhydroxyalkanoates synthases from Pseudomonas mendocina NK-01 with the same substrate specificity.

The medium-chain-length polyhydroxyalkanoate (PHAMCL) synthase genes phaC1 and phaC2 of Pseudomonas mendocina NK-01 were cloned and inserted into expression plasmid pBBR1MCS-2 to form pBBR1MCS-C1 and pBBR1MCS-C2 which were expressed respectively in the PHAMCL-negative strain P. mendocina C7 whose PHAMCL synthesis operon was defined knock out. P. mendocina C7 derivatives P. mendocina C7C1 and C7C2 carrying pBBR1MCS-C1 and pBBR1MCS-C2 respectively were constructed. Fermentation and gel permeation chromatography (GPC) revealed that P. mendocina C7C1 had higher PHAMCL production rate but its PHAMCL had lower molecular weight than that of P. mendocina C7C2. Gas chromatograph/mass spectrometry (GC/MS) analysis revealed that the two PHAMCL had similarity in monomer composition with 3HD as the favorite monomer i.e. PhaC1 and PhaC2 had the same substrate specificity. Differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and X-ray diffraction (XRD) also revealed that the two PHAMCL had the same physical properties. P. mendocina NK-01was the first reported strain whose PHAMCL synthases PhaC1 and PhaC2 had the same substrate specificity.