Engineering lactic acid bacteria for increased industrial functionality

Based on their spoilage-preventing and flavor-contributing characteristics, lactic acid bacteria (LAB) are employed as starter cultures for the fermentation of foods and feeds. In addition, several specific LAB strains are marketed on basis of their beneficial effects on the consumer's health, representing an explosively growing market for the products containing these so-called probiotics. Due to this extensive industrial use there is a strong interest in unraveling the molecular mechanisms involved in industrial robustness, cognate stress resistance, and health-promoting phenotypes of these LAB that may vary drastically between different starter and probiotic strains currently marketed. This review describes some of the post-genomic tools developed, as well as their employment for the identification of bacterial effector molecules involved in the aforementioned industrially relevant phenotypes. Furthermore, it addresses possible strategies to exploit such knowledge into the rational design of LAB strains with increased industrial functionality.     

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.     

Anti-mutagenic and immuno-stimulatory properties of lactic acid bacteria

Statistically significant antigenotoxic activity was exerted by six of nine strains of lactic acid bacteria tested (Lactobacillus delbrueckii subsp. bulgaricus, Staphylococcus carnosus, Streptococcus thermophilus, L. rhamnosus, Enterococcus faecium and En. faecalis) against nitrovin and 2-aminofluorene in Salmonella typhimurium TA100 and TA97. The mutagenic activity of both mutagens was substantially decreased by viable bacteria; cells heated to 100°C for 15 min were ineffective. In vitro, En. faecium stimulated the basic metabolic activities of human neutrophils which were essential for their antimicrobial and cytotoxic activity, whereas stimulation of guinea-pig macrophages was not so effective. Similar immuno-stimulatory effects were observed with both viable and heat-inactivated bacteria.L. Ebringer, M. Lahitová and D. Michálková are with the Institute of Molecular and Subcellular Biology, Comenius University, Odborárske nám. 5, SK-81107 Bratislava, Slovakia. M. Fereník and L. Kaáni are with the Institute of Immunology, Faculty of Medicine, Comenius University, SK-81108 Bratislava, Slovakia.     

降解嘌呤核苷乳酸菌的筛选及益生特性探索

【背景】高尿酸血症是人体内嘌呤代谢紊乱导致的一种慢性代谢疾病,利用乳酸菌降解嘌呤类物质是辅助治疗高尿酸血症的新方法。【目的】筛选高效降解嘌呤核苷的乳酸菌并对其益生特性进行研究。【方法】利用HPLC法评价乳酸菌对肌苷、鸟苷的降解效果。通过药敏性试验、体外耐受性试验及细胞黏附试验研究目标菌株的益生特性。【结果】筛选出一株发酵乳杆菌(Lactobacillus fermentum) SR2-6,对肌苷和鸟苷的降解率分别为99.26%和98.85%。该菌株对青霉素、氯霉素等5种常见抗生素不具备耐药性,在pH 2.0环境下处理4 h后菌株的存活率为76.51%,在饱腹状态下的人工肠液模拟消化4 h后活菌数仍能达到6.85 lg (CFU/mL),对Caco-2细胞的黏附数为(52.29±15.14) CFU/cell。【结论】发酵乳杆菌SR2-6能够高效降解肌苷和鸟苷且具有优良的益生特性,是预防和治疗高尿酸血症的潜在优势菌株,可作为优势菌种资源应用于相关功能产品的开发。     

Engineering metabolic highways in Lactococci and other lactic acid bacteria

Lactic acid bacteria (LAB) are widely used in industrial food fermentations and are receiving increased attention for use as cell factories for the production of food and pharmaceutical products. Glycolytic conversion of sugars into lactic acid is the main metabolic highway in these Gram-positive bacteria and Lactococcus lactis has become the model organism because of its small genome, genetic accessibility and simple metabolism. Here we discuss the metabolic engineering of L. lactis and the value of metabolic models compared with other LAB, with a particular focus on the food-grade production of metabolites involved in flavour, texture and health.     

Biological properties of antibiotic-resistant strains of lactic acid bacteria]

Lactic-acid bacteria (L. fermenti, L. acidophilus, L. delbruecki), when developing resistance to antibiotics, did not change their main biochemical, antagonistic properties and did not lose capacity for acid production. Only a decrease in their growth rate and a change in their sensitivity to the action of ultraviolet radiation were observed. Both initial and antibiotic-resistant strains were capable of taking on the mucous membrane of the large and small intestines in CBA mice.     

Aldolases of the lactic acid bacteria

Reciprocal qualitative and quantitative immunological experiments employing an anti-Pediococcus cerevisiae aldolase serum confirmed many of the interspecific relationships demonstrated previously among lactic acid bacteria with antisera prepared against the Streptococcus faecalis fructose diphosphate aldolase. The extent of immunological relatedness observed between the Lactobacillus and Pediococcus aldolases was markedly greater than that noted between Pediococcus and Streptococcus aldolases indicating that the pediococci share closer phylogenetic ties with the rod-shaped lactobacilli than with their spherical counterparts in the streptococci. In addition to confirming the existence of definitive, but distant, relationships between the lactic acid bacteria and certain gram positive nonsporeforming anaerobes, immunological cross-reactivity was also demonstrated between the pediococcal aldolases and those of Aerococcus viridans.This paper is dedicated with deepest appreciation to Prof. Roger Y. Stanier on the occasion of his 60th birthday in token of what his friendship and guidance have meant to me. — J. L.     

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。     

Engineering strategies aimed at control of acidification rate of lactic acid bacteria

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Highlights► Flux control does not reside in individual glycolytic enzymes in L. lactis. ► ATP demand does not control the glycolytic flux in L. lactis. ► Lactic acid bacteria are excellent candidates for the cell factories of the future.     

Comparative studies of lactic acid dehydrogenases in lactic acid bacteria

The stability, pH-dependence and kinetic properties of the Mn²⁺ and FDP-activated NAD-dependent lactic acid dehydrogenases from Lactobacillus casei ssp. casei (ATCC 393) and L. curvatus (DSM) 20010) were studied after the enzymes were purified to homogeneity by affinity chromatography. Both enzymes are virtually unidirectional, catalysing efficiently only the reduction of pyruvate. They are similar with respect to the effector requirement and pH-optimum. They differ, however, in their electrophoretic mobility, heat stability, pH-dependence of the Mn²⁺ requirement and several kinetic properties. It is suggested that most of these differences are caused by differences of the negative charges in the vicinity of the FDP-binding site or the site responsible for the interaction of the subunits of the enzymatically active oligomeres.Abbreviations l-LDH l-Lactic acid dehydrogenase - FDP Fructose-1,6-bisphosphate - DTE Dithioerythrol AddendumIn the case of the L. casei-LDH the shape of the NADH saturation curve is not changed by omitting the effectors FDP and Mn 2⁺. The K _M under these conditions is 3 fold higher (10.10 ^–5 M).