乳酸乳球菌乳酸亚种IMAU11823全基因组测序及胞外多糖基因簇分析

目的:乳酸乳球菌乳酸亚种IMAU11823是从内蒙古锡林郭勒盟自然发酵乳制品嚼口中分离得到的1株具有优良发酵特性且高产胞外多糖的乳酸菌。为探究其产胞外多糖的作用机制,对其进行全基因组测序并解析基因组序列信息。方法:使用PacBio SMRT三代测序技术对该菌株进行全基因组测序,采用生物信息学方法对其进行序列组装、基因预测和功能注释,并深入挖掘可能参与胞外多糖生物合成相关的基因信息。结果:乳酸乳球菌乳酸亚种IMAU11823包含1条染色体DNA(基因组大小为2 458 520 bp,GC含量为35.2%)和3个环状质粒(pIMAU11823A、pIMAU11823B、pIMAU11823C,基因组大小和GC含量分别为127 965,24 554,7 734 bp和35.7%,39.5%,32.7%),同时发现该菌株基因组内具有乳糖、纤维二糖、蔗糖、果糖、甘露糖、半乳糖转运系统和7种糖核苷酸合成相关基因以及1个胞外多糖合成基因簇epsRXCDBEF(GTF1)H(GTF2)JKM。结论:本研究揭示了乳酸乳球菌乳酸亚种IMAU11823的基因组特征,并预测了其胞外多糖的合成机制,为研究其产生的胞外多糖结构特征提供了理论依据,同时为该菌株在工业生产中的应用奠定理论基础。     

基于电子鼻和电子舌技术评价乳酸乳球菌对发酵乳风味品质的影响

目的:探究不同发酵特性的乳酸乳球菌对发酵乳品质的影响.方法:通过电子鼻与电子舌技术,结合多元统计分析对191株乳酸乳球菌所制备的发酵乳进行风味与滋味品质评价.结果:主成分分析表明,具有不同产酸和蛋白水解特性的乳酸乳球菌所制备的发酵乳风味特征呈分离趋势.Mann-Whitney分析结果表明,慢速产酸组的发酵乳芳香成分显著...     

切达干酪发酵菌种的特性测定及发酵干酪的评价

对实验室研究较为成熟的2株乳酸乳球菌进行发酵产酸、产黏测定,同时对其蛋白水解能力进行评价;并对单菌株、不同比例组合菌株制备的切达干酪进行质构特性评价、感官分析和风味物质测定。测定结果表明:乳酸乳球菌乳酸亚种KLDS4.0424是主要的产酸菌种;与商业发酵剂相比,实验室菌株的蛋白水解能力和产黏能力相对较弱;乳酸乳球菌乳酸亚种KLDS4.0424与乳酸乳球菌乳脂亚种KLDS4.0326按1∶1接种制作的干酪具有良好的成熟度、质地和风味,具备开发成干酪发酵剂的潜力。      

开菲尔(Kefir)酸牛乳酒中乳酸菌分离及发酵性能测定

对自制的开菲尔酸牛乳酒进行分离得到16株乳酸菌,通过显微镜观察及生理生化特性研究,结果为肠膜明串珠菌乳脂亚种两株,乳酸乳球菌乳酸亚种2株,乳酸乳球菌乳脂亚种2株,粪肠球菌1株,瑞士乳杆菌3株,德氏乳杆菌保加利亚亚种2株,嗜酸乳杆菌4株;经发酵性能测定,筛选出2株乳酸球菌LC2、LC6和3株乳酸杆菌LB3、LB4、LB8发酵活力较高、发酵乳组织状态及风味较好,可作为Kefir酸牛乳酒纯培养发酵剂乳酸菌的备选菌株.     

产胞外多糖乳酸球菌的分离筛选及在Mozzarella干酪中的应用

从东北传统的发酵制品大酱、糖蒜和辣酱中分离出116株乳酸菌,其中LJ35和LJ51两株菌胞外多糖产量相对较高且稳定,分别为乳酸乳球菌乳酸亚种(L.lactis subsp.lactis)和乳酸乳球菌乳脂亚种(L.lactis subsp.cremoris),胞外多糖的产量分别为62.19 mg/L和74.24 mg/L.以菌株LJ35和LJ51制作Mozzarella千酪的研究表明,添加2%LJ35或2%LJ51作发酵剂制作的Mozzarellla干酪保水性分别提高了2.1%和3.2%;同时干酪的融化性得到改善,干酪硬度降低,变得柔软.     

高加索酸奶中乳酸菌的分离与鉴定

从自然发酵的5份酸奶样品中,通过平板划线等方法分离筛选乳酸菌。经形态特征,生理生化特性及糖发酵试验等,筛选到12株乳酸菌,分别为:乳杆菌7株,其中:3株德氏乳杆菌保加利亚亚种(Lactobacillus delbrueckii subsp.bulgaricus),3株瑞士乳杆菌(Lactobacillus hel-veticus),1株罗伊氏乳杆菌(Lactobacillus reuteri);乳酸球菌5株,包括3株嗜热链球菌(Streptococcus thermophilus),2株乳酸乳球菌乳脂亚种(Lactococcus lactis subsp.Cremoris)。     

不同来源食品级乳酸菌及双歧杆菌对乳酸链球菌素敏感性的研究

目的:研究不同来源的食品级乳酸菌和双歧杆菌对乳酸链球菌素(nisin)的敏感性,为构建以nisin作为食品级筛选标记的受体乳酸菌表达系统以及筛选食品发酵、保鲜与贮藏过程中的nisin抗性乳酸菌提供科学依据.方法:采用试管稀释法研究不同来源的食品级的18株乳酸球菌、15株乳酸杆菌和5株双歧杆菌对nisin的敏感性.结果:大部分乳球菌和部分乳杆菌对nisin不敏感,但乳酸乳球菌(Lactococcus lactis)ML0230、99210,肠膜明串珠菌葡聚糖亚种(Leuconostoc mesenteroides subsp dextranicum)AS 1.2141T,嗜酸乳杆菌(Lactobacillus acidophilus)La1,德氏乳杆菌保加利亚亚种(Lactobacillus delbrueckii subsp bulgaricus)S-1、DR、LD、AS 1.2625T,长双歧杆菌(Bifidobacterium longum)Blm对nisin非常敏感.在nisin质量浓度为5 μg/mL(IU/mL)时即可抑制其生长.结论:初步筛选出17株以nisin作为食品级筛选标记的受体乳酸菌,同时筛选出21株食品发酵、保鲜与贮藏过程中的nisin抗性乳酸菌.     

新疆酸马奶中乳酸菌的多态性分析及发酵性能研究

以新疆牧民传统家庭自制酸马奶样品为研究对象,考察乳酸菌的多态性及筛选优良性状的乳酸菌菌株。通过16S r RNA基因序列分析和生理生化试验等方法对分离出的菌株进行鉴定,并进行发酵性能测试。结果表明,本实验共分离出19株菌株,包括乳酸乳球菌乳酸亚种(Lactococcus lactis subsp.lactis)(8株)、粪肠球菌(Enterococcus faecalis)(2株)、屎肠球菌(Enterococcus faecium)(2株)、嗜热链球菌(Streptococcus thermophilus)(1株)、干酪乳杆菌(Lactobacillus casei)(3株)、植物乳杆菌(Lactobacillus plantarum)(2株)和徳氏乳杆菌乳酸亚种(Lactobacillus delbrueckii subsp.Lactis)(1株)。其中,干酪乳杆菌JDB1.1505是一株产酸和产黏性能都比较突出的乳酸菌,发酵脱脂乳的滴定酸度达到了130.1°T,黏度为1420.1m Pa·s,具有良好的乳品发酵应用潜能。     

传统乳制品中乳酸菌的分离及性能研究

从内蒙古地区采集的16个传统发酵乳制品中共分离到27株乳酸菌,其中干酪乳杆菌假植物亚种4株,干酪乳杆菌1株,戊糖乳杆菌1株,阿拉伯糖乳杆菌1株,粪肠球菌1株,屎肠球菌2株,乳酸乳球菌乳酸亚种12株,格氏乳球菌2株,野生链球菌3株。分离菌株发酵10%(W/V)脱脂乳的滴定酸度平均为52.3°T,乳杆菌中IML15-1滴定酸度和黏度分别为101.8°T和1307.5mPa·s;乳酸球菌中IMS8-2的黏度达到1567.5mPa·s。     

乳酸乳球菌乳酸亚种高产胆盐水解酶发酵条件的优化研究

本文利用从藏灵菇中筛选的产胆盐水解酶的乳酸乳球菌乳酸亚种(Lactococcuslactissubsp.lactis)研究提高酶活力的环境因素。针对主要影响胆盐水解酶合成的四个因素,采用四因素三水平L9(34)正交试验确定了高产胆盐水解酶优化发酵条件:葡萄糖添加量为3%、大豆蛋白胨添加量为2%、发酵温度为37℃、接种量为2%。在优化条件下,胆盐水解酶活力是优化前的11.84倍。     

Characterization of bacteriocins from two Lactococcus lactis subsp. lactis isolates

In this study, bacteriocins from two Lactococcus lactis subsp. lactis isolates from raw milk samples in Turkey designated OC1 and OC2, respectively, were characterized and identified. The activity spectra of the bacteriocins were determined by using different indicator bacteria including Listeria, Bacillus and Staphylococcus spp. Bacteriocins were tested for their sensitivity to different enzymes, heat treatments and pH values. Loss of bacteriocin activities after alpha-amylase treatment suggested that they form aggregates with carbohydrates. Molecular masses of the purified bacteriocins were determined by SDS-PAGE. PCR amplification was carried out with specific primers for the detection of their structural genes. As a result of these studies, the two bacteriocins were characterized as nisin and lacticin 481, respectively. Examination of plasmid contents of the isolates and the results of plasmid curing and conjugation experiments showed that in L. lactis subsp. lactis OC1 strain the 39.7-kb plasmid is responsible for nisin production, lactose fermentation and proteolytic activity, whereas the 16.0-kb plasmid is responsible for lacticin 481 production and lactose fermentation in L. lactis subsp. lactis OC2 strain.     

Isolation of halotolerant Lactococcus lactis subsp. lactis from intestinal tract of coastal fish

We isolated lactic acid bacteria from the intestinal tract of the pufferfish Takifugu niphobles caught in Shimoda, Shizuoka, Japan by using MRS broth prepared with 50% seawater. Additional screening was carried out using phenotypic tests such as Gram staining, cell morphology, catalase, oxidase and fermentation of glucose. Subsequently 227 isolates screened by the phenotypic tests were subjected to species-specific PCR for Lactococcus lactis, resulting in four positive isolates. The 16S rRNA gene sequences from three isolates were highly similar to that of L. lactis subsp. lactis (DNA database accession number M58837), while that of one isolate was identical to that of Leuconostoc mesenteroides (AB023246). These isolates were characterized by API 50 CH for carbohydrate fermentation and other phenotypic criteria for salt tolerance, and the characteristics were compared with those of L. lactis subsp. lactis from a cheese starter culture. The carbohydrate fermentation profiles of these isolates were characteristic of L. lactis subsp. lactis strains, whereas the tolerance of these isolates to salt was higher than that of L. lactis subsp. lactis from the cheese starter culture: the new L. lactis isolates showed high salt tolerance in MRS-agar plates containing 200% seawater or 6% sodium chloride. This is the first report of the isolation of halotolerant strains of L. lactis subsp. lactis from a marine environment.     

乳酸乳球菌KLDS4.0325的B族维生素生物合成途径分析

为了探究乳酸乳球菌KLDS4.0325的B族维生素合成潜力,利用各类B族维生素生物合成途径的相关蛋白序列针对该菌株的氨基酸序列进行同源性搜索,并与其他9 株乳酸乳球菌的叶酸生物合成途径进行比较分析。结果表明：与参考菌株相比,乳酸乳球菌KLDS4.0325具有较为完整的叶酸和核黄素合成途径编码基因,在基因水平上可以有效合成叶酸和核黄素,具有相当大的工业潜能。     

Growth stimulation of a proteinase positive Lactococcus lactis strain by a proteinase negative Lactococcus lactis strain

Lactococcus lactis AMP15/pAMP31(D471R) is a proteinase negative, lactose negative strain with a modified oligopeptide transport system, and potential as a debittering agent due to its efficient utilization of hydrophobic peptides. Five wild L. lactis strains of dairy origin, which produced cheeses of high flavour quality, were cocultured with L. lactis AMP15/pAMP31(D471R) in an attempt to select adequate combinations of strains for use as defined cheese starters with potential debittering ability. Four of these strains, L. lactis B6, K16, M21 and P21, inhibited growth of L. lactis AMP15/pAMP31(D471R) at a level of 10(6) to 10(7) cfu mL(-1) after 24 h of incubation, even though production of bacteriocin-like compounds could only be proven for L. lactis M21. When L. lactis AMP15/pAMP31(D471R) was cocultured with the fifth strain, L. lactis N22, its growth was significantly (P<0.001) inhibited whereas growth of L. lactis N22 was significantly stimulated. The nature of the interaction was studied and it was established that L. lactis N22 is auxotrophic for folate, a compound produced and excreted by L. lactis AMP15/pAMP31(D471R).     

Bacteriophage resistance in Lactococcus lactis ssp. lactis using antisense ribonucleic acid.

Antisense RNA against a conserved bacteriophage gene when expressed in a Lactococcus lactis ssp. lactis strain renders it resistant to bacteriophage infection. Two open reading frames have been identified in a L. lactis ssp. lactis bacteriophage that are conserved in a majority of isolates. They code for an 18-kDa (designated GP18C) protein and a 24-kDa (GP24C) protein, respectively, which are arranged along with previously identified open reading frames in a tandem motif similar to other bacteriophages. The presence of gp18C and gp24C in a number of bacteriophage isolates was confirmed by polymerase chain reaction using primers specific for these regions. Plasmids bearing various fragments of gp18C, gp24C, or both were constructed such that the respective open reading frames were positioned in the antisense direction relative to the Lactococcus lactis ssp. cremoris Wg2 promoter, p59. These antisense RNA-producing vectors inhibited the efficiency of plaquing of L. lactis ssp. lactis bacteriophage phi 7-9 up to 50%; the resulting plaques were extremely small and irregular in shape. The replication of the bacteriophage was severely inhibited, and the total number decreased over the first 3 h during infection in strains expressing antisense RNA compared with the host strain alone, in which the bacteriophage number increased 10(4)-fold.     

Is thermotolerance correlated to heat-shock protein synthesis in Lactococcus lactis subsp. lactis?

Exposure of Lactococcus lactis subsp. lactis cells to a heat shock at 40 degrees C for 30 min induces thermotolerance, the increased ability of bacterial cells to survive exposure to lethal temperature (52 degrees C for 25 min). This transient state of thermal resistance is accompanied, as in Escherichia coli, by the synthesis of a new set of specific proteins termed heat-shock proteins (Hsps). Pre-treatment of the bacterial cells by antibiotics (streptomycin, spiramycin, kanamycin and erythromycin) known to act on translation, induces the major Hsps synthesis but no thermal protection; conversely, puromycin and amino acid analogues treatments, known to produce abnormal and incomplete peptides, triggers the thermotolerance state without inducing significant Hsps synthesis. These results demonstrate that heat-shock response and induced thermotolerance are not tightly correlated phenomena in L. lactis subsp. lactis.     

镉胁迫下泡菜乳酸乳球菌的形态变化

通过扫描电镜和透射电镜分别观察不同质量浓度水平的Cd2+对泡菜乳酸乳球菌（Lactococcus lactis subsp.lactis）细胞的影响,扫描电镜结果显示：Cd2+质量浓度在0、10 mg/L时,泡菜乳酸乳球菌呈椭圆形、表面光滑、菌体生长繁殖旺盛,随着Cd2+质量浓度的增加菌体细胞表面产生白色颗粒状物质、菌体细胞存活数量大幅下降（OD600 nm值由1.336下降到0.515）。当添加200 mg/L Cd2+时,几乎没有见到明显的菌体、显示有少量棱形晶状物。透射电镜结果显示：当Cd2+质量浓度为0～50 mg/L时泡菜乳酸乳球菌结构完整、细胞内容物分布均、菌体生长较为正常,当菌体暴露于100、200 mg/L Cd2+时菌体细胞出现异常现象,如细胞破裂、内容物从薄膜穿孔中释放、质壁分离等。两类电镜结果均表明：在低质量浓度Cd2+（≤50 mg/L）胁迫下,对泡菜乳酸乳球菌的生长几乎不产生影响,添加Cd2+质量浓度上升到100、200 mg/L时泡菜乳酸乳球菌正常生长受到抑制。     

Growth characteristics of Candida kefyr and two strains of Lactococcus lactis subsp. lactis isolated from Zimbabwean naturally fermented milk.

Lactic acid bacteria (LAB) and yeasts constitute part of the microflora in Zimbabwean traditional fermented cows' milk, amasi. The present study was carried out to investigate the growth characteristics of Candida kefyr 23, Lactococcus lactis subsp. lactis biovar. diacetylactis C1 and L. lactis subsp. lactis Lc261, previously isolated from amasi, in ultrahigh temperature (UHT)-treated cows' milk. The strains were inoculated into the UHT milk as both single and yeast     

乳酸乳球菌胞外多糖磷酸化的工艺优化

采用单因素和正交试验,对乳酸乳球菌胞外多糖的磷酸化工艺进行研究,探讨磷酸盐用量、反应温度、反应时间、反应pH值对乳酸乳球菌胞外多糖最终PO43-接枝量的影响。所得的乳酸乳菌球菌胞外多糖磷酸化的工艺优化条件为：胞外多糖与磷酸盐质量比为6:1、温度90℃、时间4h、pH6.0,此条件下所得PO43-的接枝量为1.639mg/g。     

Incidence of nisin Z production in Lactococcus lactis subsp. lactis TFF 221 isolated from Thai fermented foods

Lactic acid bacteria isolated from various Thai fermented foods were screened for the presence of nisin gene by using PCR with primers specific to nisin A structural gene. Only one strain, Lactococcus lactis subsp. lactis TFF 221, isolated from kung jom, a traditional shrimp paste, was found to carry a nisin gene. The TFF 221 nisin had antimicrobial activity against not only closely related lactic acid bacteria but also some foodborne pathogens. It was heat stable and inactivated by alpha-chymotrypsin and proteinase K. Some characteristics of TFF 221 nisin were found to be very similar to those of nisin A produced by Lactococcus lactis subsp. lactis NCDO 2111. Both of them had the same antimicrobial spectrum and MICs against all indicator bacteria. However, when assayed with indicator organisms, in all cases the TFF 221 nisin produced larger zones of inhibition in agar diffusion assays than the nisin A did. Sequencing of the TFF 221 nisin gene showed that it was the natural nisin variant, nisin Z, as indicated by the substitution of asparagine residue instead of histidine at position 27. The nisin determinant in strain TFF 221 was found to be located on a conjugative transposon residing in the chromosome. The ability of the nisin produced by L. lactis subsp. lactis TFF 221 to inhibit a wide range of foodborne pathogens may be useful in improving the food safety of the fermented product, especially in the Thai environment, which suffers from perennial problems of poor food hygiene.