Shi Ru Jia

Metabolic Investigation in Gluconacetobacter xylinus and Its Bacterial Cellulose Production under a Direct Current Electric Field.

The effects of a direct current (DC) electric field on the growth and metabolism of Gluconacetobacter xylinus were investigated in static culture. When a DC electric field at 10 mA was applied using platinum electrodes to the culture broth, bacterial cellulose (BC) production was promoted in 12 h but was inhibited in the last 12 h as compared to the control (without DC electric field). At the cathode, the presence of the hydrogen generated a strong reductive environment that is beneficial to cell growth. As compared to the control, the activities of glycolysis and tricarboxylic acid cycle, as well as BC productivity were observed to be slightly higher in the first 12 h. However, due to the absence of sufficient oxygen, lactic acid was accumulated from pyruvic acid at 18 h, which was not in favor of BC production. At the anode, DC inhibited cell growth in 6 h when compared to the control. The metabolic activity in G. xylinus was inhibited through the suppression of the tricarboxylic acid cycle and glycolysis. At 18–24 h, cell density was observed to decrease, which might be due to the electrolysis of water that significantly dropped the pH of cultural broth far beyond the optimal range. Meanwhile, metabolites for self-protection were accumulated, for instance proline, glutamic acid, gluconic acid, and fatty acids. Notably, the accumulation of gluconic acid and lactic acid made it a really tough acid stress to cells at the anode and finally led to depression of cell growth.

The Effect of Growth, Migration and Bacterial Cellulose Synthesis of Gluconacetobacter xylinus in Presence of Direct Current Electric Field Condition

In this study, the movement and orientation of bacteria cells were controlled by direct current(DC) electric fields, result in altering alignment of bacterial cellulose nanofiber and further changing the 3-dimensional network structure of bacterial cellulose. A modified swarm plate assay was performed to investigate the migration of Gluconacetobacter xylinus cells which exposed in DC electric field. It suggested that the cells moved toward to negative pole and with the increasement of the electric field strength the velocity will also increase. The SEM analysis demonstrated that the cellulose fiber bundles which synthesized at 1V/cm have lager diameter and a trend toward one direction. Meanwhile the growth state of G.xylinus in the presence of DC electric field was also being observed.

Chemical Characterization and Nutritional Analysis of Protein Isolates from Caragana korshinskii Kom.

Plant-based proteins are valuable supplements to compensate the gap between supply and demand in the food or feed industry. However, they lack essential amino acids, such as lysine in cereal grains and sulfur-containing amino acids in legumes, which greatly limit their wider uses for human and animals. In this study, the contents of nutritional ingredients and antinutritional factors of Caragana korshinskii Kom. and its protein isolates were quantitatively investigated. It was shown that the crude protein contents of C. korshinskii Kom. and its protein isolates obtained by alkaline extraction method (Al-CPI) and acetone precipitation method (A-CPI) were 9.1, 50.1, and 42.6%, respectively. Amino acid contents in C. korshinskii Kom., Al-CPI, and A-CPI basically exceeded the FAO/WHO (2007) reference pattern for adults except sulfur-containing amino acids. The lysine levels in C. korshinskii Kom., Al-CPI, and A-CPI were 4.1, 3.1, and 3.8 mg/100 mg crude protein respectively, which were higher than some other kinds of cereal grains. The methionine in A-CPI (1.39 mg/100 mg crude protein) was even higher than that in soybean. The antinutritional factors in C. korshinskii Kom. and Al-CPI were generally lower than those in some other kinds of legumes except total phenol and tannin. Total phenol and tannins in Al-CPI were 19.02 and 5.66 mg/g dry substance, respectively, but they were undetectable in A-CPI. This study provided a detailed analysis on nutritional and antinutritional factors in C. korshinskii Kom. and its protein isolates, indicating that they have a great potential on food and feed additives.

Rapid Identification of Microorganisms Isolated from Pickled Vegetables by MALDI-TOF Mass Spectrometry

Matrix-assisted laser desorption/ionization time-off light mass spectrometry (MALDI-TOF MS) is increasingly used as a microbial diagnostic method for species identification of pathogens. However, MALDI-TOF MS identification of food bacteria was seldom reported. Ten strains isolated from different pickled vegetables were rapid identified by MALDI-TOF MS. The results of MALDI-TOF MS were confirmed by 16S rDNA sequencing method. Different score values in MALDI-TOF MS revealed nine Leuconostoc mesenteroides and one Staphylococcus. Identification success at the species and genus levels was 90% (9/10) and 100% (10/10), respectively.16S rDNA sequencing results showed that nine stains were identified as Leuconostoc mesenteroides and one was Staphylococcus saprophyticus. Results obtained demonstrate that MALDI-TOFMS is a promising method for discriminating and identifying food bacteria.

The Open Culture of Nostoc flagelliforme with a 25 L Open Pond

The open culture is a simple, low-cost way for microalage cultivation, and the great advantage of which is that it can be easily used for mass production. This culture system is primarily used for the alga that can survive under bad or extreme conditions. N. flagelliforme is a kind autotrophic alga having the property of alkali-resistance, which makes open culture of N. flagelliforme become possible. In this study, the cultivation of N.flagelliforme with an open, 60×40×30cm rectangular glass reactor was conducted. Firstly, the open culture of N.flagelliforme was carried on without new nutrient elements supplemented into pond intermittently. During the whole process of cultivation, the pH maintained at 8-9 in order to avoid the contamination of other green alga. At the end of the cultivation, the cell density reached 0.802 g•L-1 and the exopolysaccharide concentration was 97mg•L-1. Secondly, the fed-batch cultivation was employed to increase biomass and exopolysaccharide production. At the end of the fed-batch cultivation, the biomass and exopolysaccharide of N.flagelliforme increased distinctly to 1.16 g•L-1 and 124 mg•L-1, respectively.

The Growth of Nostoc flagelliforme Cells in Desert Soil and its Ecological Effects

Nostoc flagelliforme cells obtained from liquid culture were cultivated in sand and desert soil to investigate the ecological effects of N. flagelliforme in desert area. The result showed that the N. flagelliforme cells exhibited adaptability to draught similar to the wild N. flagelliforme trichome. The growth rate of N. flagelliforme cells on the sand is much faster than that of the trichome. Determinations of the water permeability and water retention showed that the N. flagelliforme cells can improve the soil quality. The result of soil surface crusting indicated that N. flagelliforme cells can adhere to the surface of the sand particles growing and forming the biological crust.

Oriented bacterial cellulose-glass fiber nanocomposites with enhanced tensile strength through electric field

Bacterial cellulose (BC) is a kind of excellent nano-sized fibrous material produced by some microorganisms. However, commonly obtained randomly-oriented web-like form of BC nanofibers impedes achieving their full potential applications in some cases. In the present study, a facile method has been developed to orient the nanofibers through electric field. The nanofibers with an oriented structure were observed when BC producer (Gluconacetobacter xylinus) was cultured under an electric field of 10 mA. Subsequently, an oriented bacterial cellulose-glass fiber nanocomposite was prepared using a glass fiber and BC matrix under an electric field. The nanocomposites exhibited a significant improvement in tensile strength and thermostability. With an addition of 20 wt% GF, the tensile strength of the composite in perpendicular direction to DC was significantly increased to 1.44-fold of that in parallel direction. It indicated by FT-IR and XRD that the chemical structure and crystallinity of BC were not affected by addition of glass fiber. The study opens up new possibilities for direct fabrication of mechanically robust BC nanocomposites that can replace traditional BC and composite.

Integrating kinetics with thermodynamics to study the alkaline extraction of protein from Caragana korshinskii Kom.

Extraction and recovery of protein from abundant plant biomass is one potential way to improve the economic feasibility of biorefineries. However, valorization of the protein fraction is challenging due to its low yield (kg protein extraction/kg biomass). In order to reveal the limiting operation parameters, the alkaline extraction process of protein from Caragana korshinskii Kom. was investigated by an integrative analysis of kinetics and thermodynamics. Both a two‐site kinetic extraction model and a second‐order model indicated that particle size is the most pivotal factor affecting protein extraction yield. In a two‐site model, most proteins are extracted quickly from broken cells, while protein removal from the intact cells takes much longer; these are the faster and slower processes, respectively. A decrease of particle size from 20–40 to 60–80u2009mesh resulted in a decrease of C2 (protein yield in the slower process) from 14.02 to 7.32u2009mgu2009g−1, but a great increase of C1 (protein yield in the faster process) from 20.61 to 59.07u2009mgu2009g−1. However, the protein yield was dominated by the faster process when the average particle size is under 80u2009mesh. The maximum initial extraction rate was 72.20u2009mgu2009g−1u2009min−1 with the particle size of 60–80u2009mesh, almost ninefold of that with 20–40u2009mesh. Thermodynamic analysis revealed that the enthalpy change (ΔH) and entropy change (ΔS) in the protein extraction process were calculated as 21.08u2009kJu2009mol−1 and 84.76u2009Ju2009K−1, respectively. The standard free energy (ΔG) had a magnitude from −3.77 to −5.46, suggesting that the extraction process was spontaneous and physically feasible. Biotechnol. Bioeng. 2014;111: 1801–1808.

Synthesis, Characterization and Antibacterial Activity of ε-Polylysine/PVA Biodegradable Film

ε-polylysine (ε-PL) was blended with polyvinyl alcohol (PVA) to obtain biodegradable films. Blends and neat polymer films (PVA) were characterized for their structural and mechanical properties as well as antibacterial activity. The addition of ε-polylysine reduced Young modulus (Eyoung), tensile strength (TS) and elongation at break (%E) of the ε-polylysine/PVA film. The ε-polylysine/PVA film shows good antibacterial activity and therefore has potential applications in packaging industry.

Isolation of Two Strains for Microbial Desulfurization of Dibenzothiophene

Two desulfurizing strains S1 and S2 were isolated from sea water from Crude Oil Terminal at Tianjin Port. The ability of the two strains to convert dibenzothiophene (DBT) to 2-dihydroxybiphenyl (HBP) was tested by Gibbs assay, which indicated that 2-HBP existed in the metabolite. The strains S1 and S2 were identified by both 16S rDNA sequence analysis and MALDI BioTyper system as Agrobacterium tumefaciens and Acinetobacter radioresistens respectively, which could degrade 22.3% and 22.4% of DBT in 46 hours respectively.