乳酸菌胞外多糖产生菌的 筛选与初步研究

目的从牧区传统乳制品中分离获得胞外多糖产量较高的菌株,并对胞外多糖的结构和功效进行初步研究,以期能为将来生产乳酸菌胞外多糖的可行性提供数据和依据。方法通过涂布平板法从内蒙古传统发酵乳制品中分离乳酸菌,并测定胞外多糖产出量,从中筛选胞外多糖高产菌株,通过生理生化试验和16S rRNA测序鉴定菌株。采用紫外光谱法和高效液相色谱法对胞外多糖的结构进行初步分析。通过测定胞外多糖的吸湿能力和保湿能力初步评价其吸湿保湿性能。结果共分离出90株菌株,筛选出1株胞外多糖高产菌株,并鉴定出该菌株为嗜热链球菌。通过分析得出该菌株产生的胞外多糖主要由4种单糖组成,分别为甘露糖、葡萄糖、半乳糖和阿拉伯糖,其摩尔比为0.25∶3.10∶3.70∶0.10,分子量范围为1.897×10~6～7.257×10~6 Da。通过保湿性能的测定,初步确定该嗜热链球菌产生的胞外多糖有良好的保湿性。结论本实验筛选出的胞外多糖高产菌株嗜热链球菌属于益生菌,有广泛的应用价值。     

嗜酸乳杆菌与嗜热链球菌共发酵互生机理的研究

目的:对嗜酸乳杆菌和嗜热链球菌共发酵时两者的互生作用机理进行研究。方法:以质量浓度100gL脱脂乳为培养基,将嗜酸乳杆菌主要代谢产物—氨基酸,如赖氨酸、精氨酸、缬氨酸分别以0.0083mgml、0.0036mgml、0.0053mgml的量加入含嗜热链球菌脱脂乳培养基中,40℃培养,测定凝乳时间;将嗜热链球菌的代谢产物-乳酸、甲酸分别为0.1332mgml和0.075mgml的量加入含嗜酸乳杆菌脱脂乳培养基中,37℃培养,测定其发酵乳的凝乳时间。结果:嗜热链球菌发酵乳凝乳时间由12h缩短到4h,pH为4.52～4.62,吉尔涅尔度为54.23～64.74°T;嗜酸乳杆菌发酵乳的凝乳时间由16h缩短为5h,pH为4.61～4.65;且嗜酸乳杆菌在CO2环境中发酵时,发酵时间明显缩短。结论:嗜酸乳杆菌和嗜热链球菌共发酵时具有互生关系。     

粘性嗜热链球菌ST-1产胞外多糖发酵条件优化

应用响应面法对一株粘性嗜热链球菌ST-1的产胞外多糖的发酵条件进行了优化.根据单因素的实验结果,选取接种量,发酵温度,发酵时间作为考察因素,以胞外多糖的产量作为响应值,利用Box-Behnken实验设计方法,建立了胞外多糖产量与三个考察因素之间的回归方程并得到最佳发酵条件为:接种量5%,发酵时间14 h,发酵温度42℃...     

刚果红平板法筛选血链球菌胞外多糖缺失突变株

细菌胞外多糖不但能够保护细菌,防止外界环境变化和侵蚀者对菌体细胞的侵害,而且在医学微生物学中还具有特有的生物学活性, 包括抗辐射、抗氧化等特性。尽管细菌胞外多糖受到了学者的广泛关注,但胞外多糖的生物合成机制还不十分清楚。以血链球菌为模式生物,以随机插入突变机制构建的血链球菌胞外多糖形成基因文库为受试对象,建立了一种简单易行的刚果红平板法用于筛选血链球菌细胞外粘多糖形成缺失突变株的方法,为日后研究细菌胞外多糖形成机制以及临床上筛选胞外多糖缺失突变株奠定了基础。     

嗜热链球菌IMAU20246胞外多糖基因簇及其表达分析北大核心

【目的】嗜热链球菌IMAU20246是一株具有良好发酵特性且高产胞外多糖(exopolysaccharides,EPS)的菌株,但其EPS基因簇及合成途径尚不清晰。因此可通过全基因组测序及生物信息学分析菌株基因组序列,探究EPS合成及调控机制。【方法】本实验对嗜热链球菌IMAU20246进行全基因组测序并进行生物信息学分析,解析EPS生物合成相关基因簇及EPS合成途径,同时采用实时荧光定量PCR技术(quantitative real-time PCR,qRT-PCR)对其不同时间点EPS基因簇的表达进行定量分析。【结果】嗜热链球菌IMAU20246基因组中有一个18.1 kb的EPS生物合成基因簇,编码15个与EPS生物合成相关的基因。嗜热链球菌IMAU20246通过转运葡萄糖、甘露糖、果糖、半乳糖、乳糖、海藻糖、纤维二糖及蔗糖合成UDP-葡萄糖、dTDP-葡萄糖、dTDP-鼠李糖、UDP-半乳糖、UDP-呋喃半乳糖、UDP-N-乙酰葡萄糖胺和UDP-N-乙酰半乳糖胺等7种糖核苷酸。qRT-PCR的结果表明,EPS基因簇中的基因在细胞生长阶段均能表达,特别是糖基转移酶基因epsE、epsF、epsH和epsJ在培养6 h时表达量最高,此时EPS产量达到最高。【结论】本研究从基因组解析了嗜热链球菌IMAU20246 EPS基因簇及其合成途径,为菌株的进一步开发提供了理论依据。     

嗜热链球菌的特性与应用研究进展

嗜热链球菌是一种重要的工业用乳酸菌,广泛应用于发酵乳制品生产。近年来,对嗜热链球菌的研究已不仅仅停留于应用方面,而有关该菌基因组学等深层次特性机理的研究越来越多,对嗜热链球菌的研究和应用开发具有较好的参考价值。综述了嗜热链球菌的认定和应用、基因组学特征、发酵特性、噬菌体防御和共生机制等方面的研究进展,并展望了现代生物技术在嗜热链球菌特性研究中的应用前景。     

响应面法优化嗜热链球菌AR333电转化条件

【背景】嗜热链球菌AR333是本实验室从发酵乳中筛选出的一株高产活性胞外多糖乳酸菌。【目的】建立嗜热链球菌AR333高效电转化体系。【方法】通过单因素试验和Box-Behnken响应面法优化电转化条件。【结果】嗜热链球菌AR333最优电转化条件为甘氨酸浓度8.3g/L,OD_(600)为0.8,10%甘油(体积比)和0.5 mol/L蔗糖的电转缓冲液,pIB184质粒80 ng,电场强度14 kV/cm,0.4 mol/L山梨醇、2 mmol/L CaCl_2和20 mmol/L MgCl_2的LM17复苏培养基,复苏时间5 h。【结论】在最优电转化条件下,嗜热链球菌AR333电转化效率达到3.68×10~5 CFU/μg-DNA,比优化前提高了14倍,实现了嗜热链球菌AR333的高效遗传转化,为其功能解析和基因工程改造奠定基础。     

一株嗜热链球菌产多糖条件的优化

使用单因素和正交试验设计相结合的方法对培养基配方及培养条件进行优化提高嗜热链球菌AR333的胞外多糖(exopolysaccharides,EPS)产量.获得最佳培养基配方为:脱脂乳粉15％(w/v)、半乳糖1％ (w/v)、大豆蛋白胨0.5％ (w/v)、磷酸氢二钾0.1％ (w/v).最佳培养条件为:接种量3％,40℃,初始pH6.5,发酵时间16 h.优化后嗜热链球菌AR333的EPS产量可达256.97mg/L,比优化前的产量提高了3.6倍.     

唾液链球菌嗜热亚种LCX2001胞外多糖分批发酵动力学*

对唾液链球菌嗜热亚种LCX2 0 0 1生物合成胞外多糖 (EPS)的动力学进行了研究 ,基于Logistic equation方程和Luedeking piret方程 ,得到了描述发酵过程的动力学模型和模型参数。该模型反映了细胞生长、乳酸生成、EPS生物合成和基质消耗之间的关系 ,模型的拟合结果与实验值吻合较好 ,误差小于 1 0 %。     

黄原胶(Xanthan Gum)的特性、生产及应用

黄原胶是野油菜黄单孢菌分泌于胞外的中性水溶性多糖。由于其独特的流变性质而有着极其广泛的工业应用。介绍了黄原胶的生产、特性、降解以及应用,并对其应用潜力作了预测。     

Isolation and characterization of Lactobacillus delbrueckii ssp. bulgaricus and Streptococcus thermophilus from plants in Bulgaria

One of the traditional ways of preparation of yogurt starter in Bulgaria is placing a branch of a particular plant species into boiled sheep's milk maintained at about 45°C, which is further incubated until a dense coagulum is obtained. To investigate the possible origin of the yogurt starter bacteria, Lactobacillus delbrueckii ssp. bulgaricus ( L. bulgaricus ) and Streptococcus thermophilus ( S. thermophilus ), the traditional way of yogurt-starter preparation was followed. Hundreds of plant samples were collected from four regions in Bulgaria and incubated in sterile skim milk. The two target bacteria at low frequencies from the plant samples collected were successfully isolated. Phenotypic and genotypic characteristics of these bacterial isolates revealed that they were identified as L. bulgaricus and S. thermophilus . Twenty isolates of L. bulgaricus and S. thermophilus , respectively, were selected from the isolated strains and further characterized with regard to their performance in yogurt production. Organoleptic and physical properties of yogurt prepared using the isolated strains from plants were not significantly different from those prepared using commercial yogurt-starter strains.
It was therefore suggested that L. bulgaricus and S. thermophilus strains widely used for commercial yogurt production could have originated from plants in Bulgaria. To our knowledge, this is the first report on the isolation and characterization of L. bulgaricus and S. thermophilus strains from plants.     

Complete genome sequence of Streptococcus thermophilus strain ND03

Streptococcus thermophilus strain ND03 is a Chinese commercial dairy starter used for the manufacture of yogurt. It was isolated from naturally fermented yak milk in Qinghai, China. We present here the complete genome sequence of ND03 and compare it to three other published genomes of Streptococcus thermophilus strains.     

Complete genome sequence of the pigmented Streptococcus thermophilus strain JIM8232

Streptococcus thermophilus is a dairy species commonly used in the manufacture of cheese and yogurt. Here, we report the complete sequence of S. thermophilus strain JIM8232, isolated from milk and which produces a yellow pigment, an atypical trait for this bacterium.     

Growth and activity of Bulgarian yogurt starter culture in iron-fortified milk

Bulgarian yogurts were manufactured and fortified with 8, 15 and 27 mg of iron kg(-1) of yogurt. The growth and acidifying activity of the starter culture bacteria Streptococcus thermophilus 13a and Lactobacillus delbrueckii subsp. bulgaricus 2-11 were monitored during milk fermentation and over 15 days of yogurt storage at 4 degrees C. Fortifying milk with iron did not affect significantly the growth of the starter culture during manufacture and storage of yogurt. Counts of yogurt bacteria at the end of fermentation of iron-fortified milks were between 2.1 x 10(10) and 4.6 x 10(10) CFU ml(-1), which were not significantly different from numbers in unfortified yogurts. In all batches of yogurt, the viable cell counts of S. thermophilus 13a were approximately three times higher than those of L. delbrueckii subsp. bulgaricus 2-11. Greater decrease in viable cell count over 15 days of storage was observed for S. thermophilus 13a compared to L. delbrueckii subsp. bulgaricus 2-11. Intensive accumulation of lactic acid was observed during incubation of milk and all batches reached pH 4.5 +/- 0.1 after 3.0 h. At the end of fermentation process, lactic acid concentrations in iron-fortified yogurts were between 6.9 +/- 0.4 and 7.3 +/- 0.5 g l(-1). The acidifying activity of starter culture bacteria in the control and iron-fortified milks was similar. There was no increase in oxidized, metallic and bitter off-flavors in iron-fortified yogurts compared to the control. Iron-fortified yogurts did not differ significantly in their sensorial, chemical and microbiological characteristics with unfortified yogurt, suggesting that yogurt is a suitable vehicle for iron fortification and that the ferrous lactate is an appropriate iron source for yogurt fortification.     

Metabolically improved exopolysaccharide production by Streptococcus thermophilus and its influence on the rheological properties of fermented milk

Altered levels of enzymes in the central carbon metabolism in Streptococcus thermophilus increased the exopolysaccharide (EPS) production 3.3 times over that of the parent strain. The influence of enhanced EPS production on the rheological properties of fermented milk is described for engineered strains of S. thermophilus which produce different levels of EPSs.     

The production of freeze-dried immobilized cultures of Streptococcus thermophilus and their acidification properties in milk

The aim of this study was to prepare alginate-immobilized freeze-dried cultures of Streptococcus thermophilus and to compare the acidifying activities of these rehydrated cultures with classical free cell liquid inoculants. Streptococcus thermophilus BT1 grew in alginate beads and the population reached 10(10) cfu g(-1) after 6 h incubation. Re-inoculation of the beads in fresh medium with a further 6 h incubation did not improve the biomass level, but extending the incubation at 42 degrees C to 24 h caused significant death. The rehydrated immobilized cell technology (ICT) starter contained 13% free cells. In acidifying activity tests, the ICT culture had a similar acidification curve to that of a classical milk-grown free cell culture, except that it reached lower final pH values. Although the differences between the ICT and liquid cultures were not important, there were significant effects of inoculation level on lag time, maximum acidification rate and on the pH and time at which the acidification rate was at its highest.     

Continuous manufacture of yogurt. I. Optimal conditions and kinetics of the prefermentation process

The principles of a method for the continuous manufacture of yogurt, based upon a two stage system, are given. The first stage, the prefermentation of milk at 45°C to a pH of 5.7, is described. The limitations of this continuous prefermentation are experimentally determined. No change in the balance of the yogurt bacteria, Lactobacillus bulgaricus and Streptococcus thermophilus, was observed. A mathematical approach is given for starting and stopping the process.     

Complete sequencing and pan-genomic analysis of Lactobacillus delbrueckii subsp. bulgaricus reveal its genetic basis for industrial yogurt production

Lactobacillus delbrueckii subsp. bulgaricus (Lb. bulgaricus) is an important species of Lactic Acid Bacteria (LAB) used for cheese and yogurt fermentation. The genome of Lb. bulgaricus 2038, an industrial strain mainly used for yogurt production, was completely sequenced and compared against the other two ATCC collection strains of the same subspecies. Specific physiological properties of strain 2038, such as lysine biosynthesis, formate production, aspartate-related carbon-skeleton intermediate metabolism, unique EPS synthesis and efficient DNA restriction/modification systems, are all different from those of the collection strains that might benefit the industrial production of yogurt. Other common features shared by Lb. bulgaricus strains, such as efficient protocooperation with Streptococcus thermophilus and lactate production as well as well-equipped stress tolerance mechanisms may account for it being selected originally for yogurt fermentation industry. Multiple lines of evidence suggested that Lb. bulgaricus 2038 was genetically closer to the common ancestor of the subspecies than the other two sequenced collection strains, probably due to a strict industrial maintenance process for strain 2038 that might have halted its genome decay and sustained a gene network suitable for large scale yogurt production.     

Survival of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus in the terminal ileum of fistulated Göttingen minipigs

The ability of Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus administered in yogurt to survive the passage through the upper gastrointestinal tract was investigated with G?ttingen minipigs that were fitted with ileum T-cannulas. After ingestion of yogurt containing viable microorganisms, ileostomy samples were collected nearly every hour beginning 3 h after food uptake. Living L. delbrueckii subsp. bulgaricus and S. thermophilus were detected in the magnitude of 10(6) to 10(7) per gram of intestinal contents (wet weight) in all animals under investigation. A calculation of the minimum amount of surviving bacteria that had been administered is presented. Total DNA extracted from ileostomy samples was subjected to PCR, which was species specific for L. delbrueckii and S. thermophilus and subspecies specific for L. delbrueckii subsp. bulgaricus. All three bacterial groups could be detected by PCR after yogurt uptake but not after uptake of a semisynthetic diet. One pig apparently had developed an endogenous L. delbrueckii flora. When heat-treated yogurt was administered, L. delbrueckii was detected in all animals. S. thermophilus or L. delbrueckii subsp. bulgaricus was not detected, indicating that heat-inactivated cells and their DNAs had already been digested and their own L. delbrueckii flora had been stimulated for growth.