NaCl-activated extracellular proteinase from Virgibacillus sp. SK37 isolated from fish sauce fermentation

ABSTRACT:  Virgibacillus sp. SK37 exhibited high extracellular proteolytic activity in skim milk broth containing 10% NaCl. Optimum conditions of the crude proteinase were at pH 8.0 and 65 °C. The proteinase was strongly inhibited by phenylmethanesulfonyl fluoride (PMSF) and preferably hydrolyzed Suc-Ala-Ala-Pro-Phe-AMC, suggesting the serine proteinase with a subtilisin-like characteristic. Proteolytic activity increased with NaCl concentration up to 20%. Ca²⁺ activated the enzyme activity but reduced enzyme stability at 65 °C. Several proteinases with dominant molecular mass (MW) of 81, 67, 63, 50, 38, and 18 kDa were detected on native-polyacrylamide gel electrophoresis (native-PAGE) activity staining in the absence and presence of 25% NaCl. These results demonstrated that Virgibacillus sp. SK37 produced salt-activated extracellular proteinases. Virgibacillus sp. SK37 could be a promising strain for starter culture development used in fish sauce fermentation.     

裂殖壶菌发酵产DHA油脂的生产工艺优化

采用磷酸香草醛法实时监测裂殖壶菌发酵产DHA油脂的积累情况,对裂殖壶菌的基础发酵工艺进行了优化。得到裂殖壶菌生长和油脂积累的最佳培养基配方为:葡萄糖30 g/L,玉米浆粉6 g/L,蛋白胨4 g/L,硝酸钠3.6~3.9 g/L,海水晶15 g/L;在50 L的发酵罐中采用后期流加一定量的葡萄糖提高碳氮比来提高油脂积累外,通过流加3.0 g/L的大豆油来刺激菌体生长,最终经过72 h的流加培养,菌体湿重达到200 g/L,总油脂含量达到60%以上,油脂脂肪酸组成中的DHA含量占22%左右。     

转rhG-CSF基因鱼腥藻的筛选及生理特性研究

用酶联免疫方法测得转基因鱼腥藻7120-G-CSF中G-CSF蛋白最大表达量为总可溶性蛋白的0.1006%.对转基因蓝藻的生长曲线、叶绿素含量和光合放氧量测定结果表明,rhG-CSF基因转化蓝藻后,对蓝藻前中期的生长影响不大,但20d后生长速度下降,这时外源蛋白表达也达到最大值.另外对外加碳源和氮源对转基因藻生长影响做了初步探索.     

微生物谷氨酰胺转胺酶的分批发酵生产

在首先采用我们自行设计的2L小型、便易的生化反应器,对我们研究室保藏的高产酶菌株链霉菌(Streptomyces sp.)WZFF.L-M168发酵生产微生物谷氨酰胺转胺酶(MTG)过程中发酵培养基的碳源、氮源和初始pH值的影响作用进行研究,确定培养条件后,逐级扩大发酵罐规模,在20L和200L发酵罐上以在线监控技术手段直接监测分析环境因素对MTG发酵生产的作用效果,确立各级发酵罐分批发酵的生产工艺条件。结果表明:碳氮源采用葡萄糖、淀粉和多价胨,初始pH值为7.0,接种量5%～10%,发酵过程中在线控制培养温度、pH、通气量和搅拌速度等各项参数指标分别为30±0.5℃、6.6～6.9,0.8～1.1vvm和200～400r/min较为适宜。在这优化技术条件下,200L发酵罐可以稳定生产酶活在2.75U/ml以上的MTG。     

伯克霍尔德氏菌胞外酯酶催化己酸乙酯合成的研究

从变质的食用油中分离得到1株具有产己酸乙酯酯化酶能力的伯克霍尔德氏菌(Burkholderia sp.)X10,并对其发酵条件和酯化条件进行了优化。结果表明,该菌株最佳发酵条件为:淀粉4%,酵母膏3%,橄榄油4%,发酵液初始p H值6.5,培养温度30℃,转速180 r/min。最佳酯化条件为:己酸添加量2%,酯化温度35℃,酯化液初始p H4.6,振荡方式为连续振荡。优化条件下酯化酶活力由1.79 U/m L提高到3.53 U/m L,较优化前增加了97.21%。     

一株产海藻糖合成酶嗜中温芽孢杆菌的鉴定及其酶学性质

由长白山温泉附近土壤中筛选得到产海藻糖舍酶菌株，为革兰氏阳性菌，具有芽孢和鞭毛，其最适生长温度为55℃，对这一菌株进行生理生化指标测定。进一步对该菌株所产海藻糖合酶的酶学性质进行研究，酶反应最适作用pH值为7．0，在pH6．6～7．4时该酶稳定，最适作用温度为35℃，在25-45℃时该酶可稳定保存。     

Factors affecting soluble selenium removal by a selenate-reducing bacterium Bacillus sp. SF-1

High concentrations of soluble selenium, selenate and selenite, have acute and chronic toxicity toward living things. With the aim of developing a biological process for selenium removal, the effects of a variety of parameters on the reduction of soluble selenium by a Bacillus sp. strain SF-1, which is capable of reductively transforming selenate into selenite and, subsequently, into nontoxic insoluble elemental selenium, were studied. The bacterial strain could effectively reduce 20 mM of selenate to selenite and 2 mM of selenite to elemental selenium in the presence of an appropriate carbon source and in the absence of oxygen. The reduction rate of selenate to selenite was much higher than that of selenite to elemental selenium, resulting in the transient accumulation of selenite during selenate reduction. The selenate reduction rate increased with increases in the selenate concentration up to 20 mM, while the rate of selenite reduction decreased sharply at selenite concentrations of more than 2 mM. The elemental selenium transformed from selenate via selenite was found both inside and outside the cells. Bacillus sp. SF-1 was able to utilize a variety of organic acids or sugars as a carbon source in selenate reduction. Although the copresence of sulfate did not inhibit selenate reduction, it was completely inhibited by some other oxyanions, including nitrate. A model sequencing batch system using the bacterial strain was developed and exhibited good performance in the treatment of wastewater containing high concentrations of selenate.     

Algicidal effect of bacterial isolates of Pedobacter sp. against cyanobacterium Microcystis aeruginosa

The aim of this study was to isolate algicidal bacteria so as to control harmful cyanobacterium Microcystis aeruginosa (M.aeruginosa) blooms using biological methods. Nine bacterial strains were isolated to inhibit the growth of M. aeruginosa, among which the MaI11-5 bacterial strain exhibited remarkable algicidal activity against M. aeruginosa cells during the test. Based on the 16S rDNA analysis, the isolated MaI11-5 was identified as Pedobacter sp. through morphology and homology research. The results of cocultivation of the cyanobacteria with MaI11-5 algicidal isolates showed obvious algicidal activity against cyanobacterial cells. The algicidal effect of MaI11-5 exceeded 50% after two days, exceeded 70% after four days, and reached 80% after seven days. The observation results with a scanning electron microscope showed that the cyanobacterial cells aggregated and produced mucous-like substances when cocultivated with the algicidal bacteria. The results indicated that the MaI11-5 bacterial strain may possess a novel function for controlling harmful blooms and further studies will provide new insights into its role in water environment.     

Histamine Formation in Fish Sauce Production

ABSTRACT: The formation of histamine in fish sauce made from Stolephorus sp was studied. In the first experiment, fish were iced on board and mixed with salt at the factory, while in the second experiment fish were mixed with salt on board collection vessels. Eight batches were fermented for 12 mo. Histamine levels increased during fermentation to 22 to 159 and 589 to 686 ppm in the first and second experiments respectively. Good correlation between histamine levels in raw material and final products was found. It was concluded that histamine was formed both in the raw material and during fermentation. It was speculated that histidine decarboxylase enzymes formed prior to fermentation produced histamine during fermentation.