大麻韧皮果胶分解菌株的分离与鉴定

用海水和清水对大麻纤维进行浸泡处理,9d后浸泡液用梯度稀释至体积分数为0·01%,然后涂布在培养基平板上,经培养、分离、纯化,挑选数量优势的单个菌落。分别得到1309和2508这2种具有较强果胶分解能力的菌株,这2个菌株均呈革兰氏阴性,菌株1309有数根极毛运动的直杆菌,菌株2508为单极毛运动的端圆直杆菌。通过Biolog分析,初步确定菌株1309和2508分别属于假单胞菌和寡养单胞菌属的嗜麦芽寡养单胞菌。     

大蒜素对假单胞菌生长动力学模型的影响

研究添加大蒜素对假单胞菌液体和固体生长动力学模型的影响。结果显示：在液态纯培养条件下,随着大蒜素添加量的增加,假单胞菌生长动力学模型中的延滞期数值从1.9136降到－0.4665,最大比生长速率数值变为负值,从0.9107降到－0.0159;在冷鲜猪肉基质上,添加大蒜素后其生长动力模型中的延滞期数值从1.9796增到5.6249,最大比生长速率数值从1.0291降到0.8615。添加大蒜素对两个模型中最大比生长速率数值的影响趋势是一致的。本实验初步说明添加大蒜素对液体模型中最大比生长速率数值的影响,在一定程度上可以推断其对固体基质上假单胞菌的生长的影响。     

Nitrile Hydratase Activity of a Recombinant Nitrilase

Appreciable amounts of amide are formed in the course of nitrile hydrolysis in the presence of recombinant nitrilase from Pseudomonas fluorescens EBC 191, depending on the α‐substituent and the reaction conditions. The ratio of the nitrilase and nitrile hydratase activities of the enzyme is profoundly influenced by the electronic and steric properties of the reactant. In general, amide formation increased when the α‐substituent was electron‐deficient; 2‐chloro‐2‐phenylacetonitrile, for example, afforded 89 % amide. We found, moreover, that (R)‐mandelonitrile was hydrolysed with 11 % of amide formation whereas 55 % amide was formed from the (S)‐enantiomer; a similar effect was found for the O‐acetyl derivatives. A mechanism that accomodates our results is proposed.     

A novel enzymatic approach to the massproduction of L-galactose from L-sorbose

Wild-type strain of Pseudomonas cichorii ST-24 was unable to grow on D -psicose and inductively produced D -tagatose 3-epimerase (D -TE) with D -tagatose as an inducer. We have isolated a constitutive mutant, designated strain Ka75, which had acquired a new ability to grow on a mineral salts medium containing D -psicose as a sole carbon source. The D -psicose-metabolizing mutant synthesized a high level of D -TE. When grown on the culture medium supplemented with Mn(2+), the mutant strain produced around 250-fold higher activity than did the parent strain. Enzymatic properties of the constitutive enzyme were similar to those of the wild-type. Using the immobilized D -TE and recombinant L-rhamnose isomerase (L-RhI) from Escherichia coli strain JM109, a two-step enzymatic reaction was performed for massproduction of a rare aldo-hexose monosaccharide, L-galactose, from a common one, L-sorbose. In the first step, L-sorbose was epimerized to L-tagatose in a yield of 28%. The L-tagatose obtained was utilized as a starting material for L-galactose preparation by the immobilized L-RhI. At equilibrium, approximately 30% L-tagatose was isomerized to L-galactose. Finally, 7.5 g of L-galactose was obtained from 100 g of L-sorbose, viz an overall yield of 7.5%. The product obtained was purified and identified to be L-galactose by specific optical rotation and high performance liquid chromatography (HPLC) analysis, and was ultimately confirmed by (13)C nuclear magnetic resonance ((13)C NMR) and IR spectra.     

Ozone is the most effective disinfectant for dental treatment units: Results after 8 years of comparison

The method of disinfecting water in dental treatment units using ozone‐containing water was first described 10 years ago. In an investigational period over the last 8 years, waters from the outlets of 14 treatment units were examined microbiologically in a total of 240 tests. Twelve of the treatment units, employing hydrogen peroxide/silver ion disinfection ‐ after repeated sanitization ‐ regularly exceeded the limits laid down in the regulations governing water purity, and Pseudomonas aeruginosa could be detected at 181 water outlets. However, germs could hardly be detected in any of the tests of waters sampled from the two treatment units using ozonated water disinfection.     

Stereoselective acylation of Dl-menthol in organic solvents by an immobilized lipase from Pseudomonas cepacia with vinyl propionate

An effective lipase-catalyzed stereoselective transesterification of (±)-menthol in organic solvent with vinyl propionate as acylating agent is described. Immobilization by adsorption and the presence of molecular sieves improved the formation of (±)-menthyl propionate by lipase (PS-30) from Pseudomonas cepacia. The reaction time course, mole ratio of substrates, temperature, amount of enzyme, as well as the effect of various organic solvents, were examined for their influence on the enzymatic stereoselective formation of (−)-menthyl propionate. Among the parameters studied, the stereospecificity toward (−)-menthol decreased significantly as temperature increased but the yields of both enantiomers increased. Organic solvents with log P (partition coefficient) values above 3.5 gave higher yield and stereoselectivity than solvents with lower log P values.     

Biofilm Matrix and Its Regulation in Pseudomonas aeruginosa

Biofilms are communities of microorganisms embedded in extracellular polymeric substances (EPS) matrix. Bacteria in biofilms demonstrate distinct features from their free-living planktonic counterparts, such as different physiology and high resistance to immune system and antibiotics that render biofilm a source of chronic and persistent infections. A deeper understanding of biofilms will ultimately provide insights into the development of alternative treatment for biofilm infections. The opportunistic pathogen Pseudomonas aeruginosa, a model bacterium for biofilm research, is notorious for its ability to cause chronic infections by its high level of drug resistance involving the formation of biofilms. In this review, we summarize recent advances in biofilm formation, focusing on the biofilm matrix and its regulation in P. aeruginosa, aiming to provide resources for the understanding and control of bacterial biofilms.     

Novel approach to fabricate polycarbonate antibacterial superhydrophobic surfaces

A novel approach to fabricate a stable polycarbonate (PC) surface with superhydrophobicity and antibacterial properties obtained by use the phase separation and solvent/non-solvent selected method without any use to surface chemical modification materials, with high chemical stability. At the same time a systematic study of dependence surface morphology on the acetone/DMF solvent mixture treatment. In medical devices, the bacterial attachment onto the surface of polymers such as a PC is influenced by the physicochemical properties of the polymers, including surface roughness and hydrophobicity. The resulting surfaces demonstrated that the water CA of the PC surface was 154 ± 2° with excellent inhibition percentage of two bacteria. FESEM showed that the surface structure comprised branches or petals outside the ‘plant seabeds’ with a hierarchical micro-/nano-binary formation, in addition to related AgNps with a rough surface. In order to test the stability and properties of the PC surfaces, Pseudomonas aeruginosa and Acinetobacter baumannii suspensions in ‘Amide Organic’ was poured above the surface and allowed to settle on top of the surface for several minutes, then, the Anti-adhesive effect of colonies bacteria was evaluated and the results showed the very small percentage of bacteria was adhesive on surfaces.     

Properties of poly(AAc‐co‐HPMA‐cl‐EGDMA) hydrogel‐bound lipase of Pseudomonas aeruginosa MTCC‐4713 and its use in synthesis of methyl acrylate

Microbial lipases (E.C. 3.1.1.3) are preferred biocatalysts for the synthesis of esters in organic solvents. Various extracellular thermoalkaliphilic lipases have been reported from Pseudomonas sp. In the present study, a purified alkaline thermoalkalophilic extracellular lipase of Pseudomonas aeruginosa MTCC‐4713 was efficiently immobilized onto a synthetic poly(AAc‐co‐HPMA‐cl‐EGDMA) hydrogel by adsorption and the bound lipase was evaluated for its hydrolytic potential towards various p‐nitrophenyl acyl esters varying in their C‐chain lengths. The bound lipase showed optimal hydrolytic activity towards p‐nitrophenyl palmitate (p‐NPP) at pH 8.5 and temperature 45°C. The hydrolytic activity of the hydrogel‐bound lipase was markedly enhanced by the presence of Hg²⁺, Fe³⁺, and NH salt ions in that order. The hydrogel‐immobilized lipase (25 mg) was used to perform esterification in various n‐alkane(s) that resulted in ～ 84.9 mM of methyl acrylate at 45°C in n‐heptane under shaking (120 rpm) after 6 h, when methanol and acrylic acid were used in a ratio of 100 mM:100 mM, respectively. Addition of a molecular sieve (3Å × 1.5 mm) to the reaction system at a concentration of 100 mg/reaction vol (1 mL) resulted in a moderate enhancement in conversion of reactants into methyl acrylate (85.6 mM). During the repetitive esterification under optimum conditions, the hydrogel‐bound lipase produced 71.3 mM of ester after 10th cycle of reuse. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci 104: 183–191, 2007     

Microbial degradation of phosmet on blueberry fruit and in aqueous systems by indigenous bacterial flora on lowbush blueberries (Vaccinium angustifolium)

ABSTRACT:  Phosmet-adapted bacteria isolated from lowbush blueberries ( Vaccinium angustifolium ) were evaluated for their ability to degrade phosmet on blueberry fruit and in minimal salt solutions. Microbial metabolism of phosmet by isolates of Enterobacter agglomerans and Pseudomonas fluorescens resulted in significant reductions ( P < 0.05; 33.8%) in phosmet residues on blueberry fruit. Degradation was accompanied by microbial proliferation of phosmet-adapted bacteria. Preferential utilization of phosmet as a carbon source was investigated in minimal salt solutions inoculated with either E. agglomerans or P. fluorescens and supplemented with phosmet or phosmet and glucose. Microbial degradation concurrent with the proliferation of P. fluorescens was similar in both liquid systems, indicative of preferential utilization of phosmet as an energy substrate. E. agglomerans exhibited the ability to degrade phosmet as a carbon source, yet in the presence of added glucose, phosmet degradation occurred within the 1st 24 h only followed by total population mortality resulting in no appreciable degradation. Characteristic utilization of glucose by this isolate suggests a possible switch in carbon substrate utilization away from phosmet, which resulted in toxicity from the remaining phosmet. Overall, microbial metabolism of phosmet as an energy source resulted in significant degradation of residues on blueberries and in minimal salt solutions. Thus, the role of adapted strains of E. agglomerans and P. fluorescens in degrading phosmet on blueberries represents an extensive plant–microorganism relationship, which is essential to determination of phosmet persistence under pre- and postharvest conditions.