生物钟的基因调控

从细菌到哺乳动物的大多数生物都存在分子时钟,也就是生物钟。它的存在使生物的生理,生化,行为表现出以24小时为周期的节律性。本文从基因组成以及节律发生的分子机制等方面,对昼夜节街生物钟进行综述。     

鲜切花保鲜相关调控基因研究进展

对切花保鲜相关调控基因：ACC氧化酶基因（CAO）,ACC合成酶基因（ACS）,ert-1基因和切花保鲜相关调控因子;乙醇、乙醛、DPSS和钴等做一综述。     

调控胚胎发育的基因

胚胎发育是一个沿时空顺序坐标在形态上剧烈变化,既复杂又充满神秘色彩的过程,对它的研究由来已久。孟德尔（Ｍｅｎｄｅｌ,１９００）和摩尔根（Ｍｏｒｇａｎ）的遗传研究,使生物学家们开始关注突变引起体形奇特性变化的重要性。Ｂｒｉｄｇｅｓ（１９１５）阐述了果蝇...     

基因治疗中的基因调控研究进展

基因治疗的目的是将导入的外源基因能够得到时序上、水平上的正确表达,其产物发挥治疗作用。目的基因表达的调控是影响基因治疗效果的一个重要因素。本文系统介绍了基因靶技术在基因治疗中的地位,提高逆转录病毒载体滴度的方法,逆转录病毒载体与目的基因序列的影响,反式激活提高目的基因应用以及对基因治疗中目的基因表达调控的展望。     

植物基因的人工调控表达

通过增加或减少特定诱导物，可精确调节目的的基因上游构建的“基因开关”，实现外源目的基因的准确调控，使外源基因在植物体内适时、适量、有效地表达。因此构建一个拥有“基因开关”的人工调控表达系统是势在必行的，该系统的成功构建也将有利于提高转基因植物广泛应用的可能性。     

基因与学习记忆调控

近年,有关基因与学习记忆调控的研究引人注目。实验显示：（１）ｃ－ｆｏｓ等即刻早期基因（ＩＥＧｓ）的激活是学习记忆形成的必要条件,长时程增强（ＬＴＰ）诱出的同时也伴有ＩＥＧｓ的激活;（２）应用转基因技术获得α－ＣａＭＫⅡ、Ｆｙｎ和Ｎ－ＣＡＭ等基因突变的小鼠,均表现明显的空间学习记忆障碍,以及ＬＴＰ诱导和维持障碍;（３）果蝇单基因（ｄｎｃ,ｒｕｔ等）突变体的学习记已能力明显下降,其机制与突触可塑性的改     

真核基因转录的负调控机理

本通过对目前关于真核基因表达调控方面研究成果的综合分析,提出了真核基因转录的十种负调控机理,即竞争作用、复制作用、隔离作用、隐蔽作用、沉默作用、变构作用、修饰作用、锁合作用、反义作用及转座作用,并引证进行了初步讨论。     

Evaluation of lactic acid bacteria autolysate for the supplementation of lactic acid bacteria fermentation

At the end of culture in a carbon-limited medium, i.e. the best conditions for subsequent autolysis, lactic acid bacteria were harvested and autolysed at 50 °C for 24 h. The resulting supernatant was then successfully tested as a substitute for industrial yeast extract for the supplementation of whey permeate and its conversion into lactic acid: for almost equivalent total nitrogen amounts of both supplements, the same growth and production rates were recorded.     

Biogenic amine production by lactic acid bacteria isolated from cider

AIMS: To study the occurrence of histidine, tyrosine and ornithine decarboxylase activity in lactic acid bacteria (LAB) isolated from natural ciders and to examine their potential to produce detrimental levels of biogenic amines. METHODS AND RESULTS: The presence of biogenic amines in a decarboxylase synthetic broth and in cider was determined by reversed-phase high-performance liquid chromatography (RP-HPLC). Among the 54 LAB strains tested, six (five lactobacilli and one oenococci) were biogenic amine producers in both media. Histamine and tyramine were the amines formed by the LAB strains investigated. Lactobacillus diolivorans were the most intensive histamine producers. This species together with Lactobacillus collinoides and Oenococcus oeni also seemed to produce tyramine. No ability to form histamine, tyramine or putrescine by Pediococus parvulus was observed, although it is a known biogenic amine producer in wines and beers. CONCLUSIONS: This study demonstrated that LAB microbiota growing in ciders had the ability to produce biogenic amines, particularly histamine and tyramine, and suggests that this capability might be strain-dependent rather than being related to a particular bacterial species. SIGNIFICANCE AND IMPACT OF THE STUDY: Production of biogenic amines by food micro-organisms has continued to be the focus of intensive study because of their potential toxicity. The main goal was to identify the microbial species capable of producing these compounds in order to control their presence and metabolic activity in foods.     

Pediocin production by recombinant lactic acid bacteria

Production of the anti-listerial bacteriocin, pediocin, by lactic acid bacteria (LAB) transformed with the cloning vector pPC418 (Ped⁺, 9.1 kb) was influenced by composition of media and incubation temperature. Maximum pediocin production, tested against Listeria innocua, by electrotransformants of Lactococcus lactis ssp. lactis was measured in tryptone/lactose/yeast extract medium after 24 h growth at 30 °C, while incubation at 40 °C was optimum for Ped⁺ transformants of Streptococcus thermophilus and Enterococcus faecalis. The amount of pediocin produced by S. thermophilus in skim milk and cheese whey supplemented with 0.5% yeast extract was estimated as 51000 units ml^–1 and 25000 units ml^–1, respectively. Pediocin production remained essentially unchanged in reconstituted skim milk or whey media diluted up to 10-fold. The results demonstrate the capacity of recombinant strains of LAB to produce pediocin in a variety of growth media including skim milk and inexpensive cheese whey-based media, requiring minimum nutritional supplementation.     

Genomics of lactic acid bacteria

Lactic acid bacteria (LAB) are found to occupy a variety of ecological niches including fermented foods as well as mucosal surfaces of humans and other vertebrates. This review is based on the genomic content of LAB that is responsible for the functional and ecological diversity of these bacteria. These genomes reveal an ongoing process of reductive evolution as the LAB have specialized to different nutritionally rich environments. Species-to-species variation in the number of pseudogenes as well as genes directing nutrient uptake and metabolism reflects the adaptation of LAB to food matrices and the gastrointestinal tract. Although a general trend of genome reduction was observed, certain niche-specific genes appear to be recently acquired and appear on plasmids or adjacent to prophages. Recent work has improved our understanding of the genomic content responsible for various phenotypes that continue to be discovered, as well as those that have been exploited by man for thousands of years.     

Vanillin production from simple phenols by wine-associated lactic acid bacteria

AIMS: The ability of lactic acid bacteria (LAB) to metabolize certain phenolic precursors to vanillin was investigated. METHODS AND RESULTS: Gas chromatography-mass spectrometry (GC-MS) or HPLC was used to evaluate the biosynthesis of vanillin from simple phenolic precursors. LAB were not able to form vanillin from eugenol, isoeugenol or vanillic acid. However Oenococcus oeni or Lactobacillus sp. could convert ferulic acid to vanillin, but in low yield. Only Lactobacillus sp. or Pediococcus sp. strains were able to produce significant quantities of 4-vinylguaiacol from ferulic acid. Moreover, LAB reduced vanillin to the corresponding vanillyl alcohol. CONCLUSIONS: The transformation of phenolic compounds tested by LAB could not explain the concentrations of vanillin observed during LAB growth in contact with wood. SIGNIFICANCE AND IMPACT OF THE STUDY: Important details of the role of LAB in the conversion of phenolic compounds to vanillin have been elucidated. These findings contribute to the understanding of malolactic fermentation in the production of aroma compounds.     

乳酸菌对真菌毒素的脱毒作用研究进展

真菌毒素广泛存在于农业产品中,对人和动物的健康构成巨大威胁。乳酸菌作为一种公认安全的微生物,在食品生物减毒方面具有巨大的应用潜力,成本低廉且不会对食品品质及生态环境造成不良影响。文章主要根据近年来国内外研究进展,阐述乳酸菌对食品和饲料中几种常见真菌毒素的脱毒作用(抑制真菌生长、毒素的吸附和降解),关注乳酸菌在生物脱毒方面的实际应用,为乳酸菌在食品保鲜领域的应用提供理论指导。     

乳酸菌的系统分类概况

乳酸菌是重要的益生菌资源,在食品、农业、化工业、医学等领域具有广阔的应用前景。目前,人们熟知的乳酸菌主要集中在乳杆菌属、双歧杆菌属、链球菌属、肠球菌属、乳球菌属、片球菌属和明串珠菌属等少数属种。为了拓宽人们对乳酸菌的认知,本文就乳酸菌的系统分类学进行阐述。在系统分类学上,乳酸菌分别隶属于厚壁菌门4纲7目18科39属653种和放线菌门2纲2目3科12属88种。最后,对乳酸菌的益生作用、安全性与有效来源、益生潜能的体外评价指标等进行简要的讨论。     

Degradation of free and sulfur-dioxide-bound acetaldehyde by malolactic lactic acid bacteria in white wine

AIMS: Acetaldehyde is the major carbonyl compound formed during winemaking and has implications for sensory and colour qualities of wines as well as for the use of the wine preservative SO(2). The current work investigated the degradation of acetaldehyde and SO(2)-bound acetaldehyde by two commercial Oenococcus oeni starters in white wine. METHODS AND RESULTS: Wines were produced by alcoholic fermentation with commercial yeast and adjusted to pH 3.3 and 3.6. While acetaldehyde was degraded rapidly and concurrently with malic acid at both pH values, SO(2)-bound acetaldehyde caused sluggish bacterial growth. Strain differences were small. CONCLUSIONS: Efficient degradation of acetaldehyde can be achieved by commercial starters of O. oeni. According to the results, the degradation of acetaldehyde could not be separated from malolactic conversion by oenococci. While this may be desirable in white winemaking, it may be necessary to delay malolactic fermentation (MLF) in order to allow for colour development in red wines. SO(2)-bound acetaldehyde itself maybe responsible for the sluggish or stuck MLF, and thus bound SO(2) should be considered next to free SO(2) in order to evaluate malolactic fermentability. SIGNIFICANCE AND IMPACT OF THE STUDY: The current study provides new results regarding the metabolism of acetaldehyde and SO(2)-bound acetaldehyde during the MLF in white wine. The information is of significance to the wine industry and may contribute to reducing the concentration of wine preservative SO(2).     

Exocellular polysaccharides produced by lactic acid bacteria

Abstract The production of homopolysaccharides (dextrans, mutans) and heteropolysaccharides by lactic acid bacteria, their chemical composition, their structure and their synthesis are outlined. Mutans streptococci, which include Streptococcus mutans and S. sobrinus produce soluble and insoluble α-glucans. The latter may contain as much as 90%α-1–3 linkages and possess a marked ability to promote adherence to the smooth tooth surface causing dental plaque. Dextrans produced by Leuconostoc mesenteroides are high molecular weight α-glucans having 1–6, 1–4 and 1–3 linkages, varying from slightly to highly branched; 1–6 linkages are predominant. Emphasis is put on exopolysaccharide producing thermophilic and mesophilic lactic acid bacteria, which are important in the dairy industry. The produced polymers play a key role in the rheological behaviour and the texture of fermented milks. One of the main problems in this field is the transitory nature of the thickening trait. This instability is not yet completely understood. Controversial results exist on the sugar composition of the slime produced, but galactose and glucose have always been identified with galactose predominating in most cases.