Lactic Acid Bacteria
Author: Aceme Nyika
Easy-to-read handbook for postgraduate students and their supervisors. Explains complex research concepts and methodologies in simple terms.
LactobacillusLactobacillus is a genus of Gram-positive facultative anaerobic or microaerophilic bacteria. In humans they are symbiotic and are found in the gut flora. Lactobacillus species are used for the production of yogurt, cheese, sauerkraut, pickles, beer, wine, cider, kimchi, chocolate and other fermented foods, as well as animal feeds such as silage. In recent years much interest has been shown in the use of lactobacilli as probiotic organisms and their potential for disease prevention in humans and animals read more ...
Lactic Acid Bacteria with Anti-Cancer ActivitiesBeneficial bacteria include Lactobacillus and Bifidobacterium spp. and other lactic acid bacteria (LAB) commonly known as probiotics. LAB possesses numerous potential therapeutic properties including anti-inflammatory and anti-cancer activities and other features of interest. In recent years, studies with in vitro cell culture and animal models that clearly demonstrated protective effects of LAB for anti-tumor and anti-cancer effects. Dietary administration of LAB alleviated the risks of certain types of cancers and suppressed colonic tumor incidence, volume and multiplicity induced by various carcinogens in different animal models. Oral administration of LAB effectively reduced DNA adduct formation, ameliorated DNA damage and prevented putative preneoplastic lesions such as aberrant crypt foci induced by chemical carcinogens in the gastrointestinal (GI) tract of various animal models. LAB also increased the latency period and survival rates in test animals when challenged with carcinogenic agents. Reports also indicated that LAB cultures administered to animals inhibited liver, colon, bladder and mammary tumors, highlighting potential systemic effects of probiotics with anti-neoplastic activities read more ...
Medicinal Uses of Lactic Acid BacteriaMost probiotic strains belong to the genus Lactobacillus. The promising results of a first generation of probiotic microbes, evaluated in animal models as well as natural infections in animals and humans indicate a promising future for coming generations of probiotics. Antibiotic-associated, travellers' and pediatric diarrhea have been most studied, and more recently, inflammatory bowel disease and irritable bowel syndrome. Probably future probiotics will contain mixes of strains with complementary characteristics, tailormade for different gastrointestinal diseases, vaginosis or as delivery systems for vaccines, immunoglobulins and other protein based therapies read more ...
Exopolysaccharide Formation by Lactic Acid BacteriaLactic acid bacteria (LAB) synthesise a wide variety of exopolysaccharides (EPS); these polysaccharides are synthesised extracellularly from sucrose by glycansucrases, or intracellularly by glycosyltransferases from sugar nucleotide precursors. Biofilm formation, stress resistance and sucrose utilisation are clearly linked to the formation of EPS in individual species of LAB. The high frequency of homopolysacharide (HoPS) and heteropolysaccharide (HePS) producing LAB in the oral cavity and intestinal ecosystems argues in favour for an important role of EPS formation for the persistence of LAB in these habitats. The intricate regulatory network controlling the expression of glycansucrases in oral streptococci is in keeping with the contribution of HoPS and extracellular glycansucrases to biofilm formation and persistence in the oral cavity. EPS production by intestinal lactobacilli may play a comparable role. Glycansucrases in Lb. reuteri of HoPS and FOS production are regulated in response to stress sensed by the cytoplasmic membrane. The products of glycansucrases improve survival of lactobacilli in a scenario characterised by strong fluctuations in water activity, temperature, pH, and nutrient supply, and the presence of natural inhibitors. Because the expression of glycansucrases in many strains of lactobacilli and Leuconostoc species is induced by sucrose, the contribution of glycansucrases to sucrose catabolism may be their main ecological role in some strains read more ...
Biosynthesis of Exopolysaccharides Produced by Lactic Acid BacteriaExopolysaccharides (EPS) produced by lactic acid bacteria (LAB) can be classified according to the chemical composition and biosynthesis mechanism as homopolysaccharides (HoPS) and heteropolysaccharides (HePS). HoPS are composed of a single monosaccharide type, either glucose or fructose, and they are polymerised extracellularly by means of glycansucrases, sucrose being the donor of the corresponding sugar moiety. These α- or β-D-glucans and β-fructans are polymers of high molar mass (≥ 1 x106 Da) which can have different degrees of branching and they are usually produced in amounts higher than 1 g/L, although this value varies according to the strain and the production conditions. The glucansucrase and fructansucrase enzymes present a conserved functional structure in which four domains can be recognized, although enzymes produced by different strains do not share similar sequences. The HePS are built up of repeating unit structures of two or more types of monosaccharides, substituted monosaccharides and other organic and inorganic molecules. To date, around 42 different unique structures comprising from di- to octasaccharides have been described. Galactose, glucose, rhamnose and to a lower extent N-acetyl-glucosamine and N-acetyl-galactosamine are present in their composition. The HePS biosynthesis is a complex process not fully understood, that involves the activity of several specific, as well as housekeeping, enzymes which also participate in the metabolism of carbohydrates and in the synthesis of some components of the cell-wall. The genes involved in HePS synthesis are organised in eps clusters that share a common structural organization in which genes involved in regulation, export, polymerisation and chain length determination, as well as glycosyltransferases responsible for the intracellular assembly of the repeated units, can be recognised read more ...
Commercial Exploitation of Exopolysaccharides from Lactic Acid BacteriaLactic acid bacteria play a crucial role in various food fermentations. Several strains can produce long chain sugar polymers called exopolysaccharides (EPS). These can be classified due to different criteria e.g. the composition of different or just one kind of sugar monomer in hetero- and homopolysaccharides. While heteropolysaccharides are intensively used as additives in milk products, homopolysaccharides can be introduced in sourdough products influencing structural quality, baking ability and reducing bread staling factors. Additionally, beneficial effects on enteral health are possible. An example for industrial use of EPS in bakery products is the application of dextran in panettone and other breads. Also the addition of non-bacterial hydrocolloids is well established in industrial baking. Several investigations concerning the replacement of these additives by bacterial EPS have been made and provide data of dough and bread parameters such as textural factors, water retention and moisture and specific bread volume. Practically no information is available on the effects of bacterial EPS in other fermented foods such as fermented meat products, sauerkraut or vinegar. EPSs can be as defined additives or alternatively via in situ production by starter cultures. The addition of purified EPS has to be labelled on the end product, which is a disadvantage since consumers demand for fewer additives in foods. On the other hand, in situ production appears to be less effective in traditional wheat and rye dough systems due to strain-dependent acid formation, which may be required but counteracts positive EPS effects. Forthcoming chances of EPS applications may therefore lie within special applications as in gluten free breads where both, reduced pH and EPS should have synergistic positive effects on structure read more ...
Nutritional and Functional Benefits of Exopolysaccharides from Lactic Acid BacteriaThe quest to find food ingredients with valuable bioactive properties has encouraged interest in exopolysaccharides (EPSs) from lactic acid bacteria (LAB). Functional food products that offer health and sensory benefits beyond their nutritional composition are becoming progressively more important in the food supply chain. Informed consumers are becoming increasingly more health conscious and more aware that disease prevention can be effected through dietary means and, more specifically, by particular components of foods. Although the sensory benefits of EPSs are now well established, more knowledge to fully understand how these polysaccharides can impact on human health and nutrition is needed. Because of the wide variation in molecular structures of EPSs, and the complexity of the mechanisms by which physical changes in foods and bioactive effects are elicited, the future commercial development of EPS-producing cultures and ingredients will depend heavily upon this platform of knowledge read more ... Further reading:
- Lactobacillus Molecular Biology: From Genomics to Probiotics
- Bacterial Polysaccharides: Current Innovations and Future Trends
- MALDI-TOF Mass Spectrometry in Microbiology
- Climate Change and Microbial Ecology: Current Research and Future Trends
- Gas Plasma Sterilization in Microbiology: Theory, Applications, Pitfalls and New Perspectives
- Flow Cytometry in Microbiology: Technology and Applications
See also: Current microbiology books
- Lactobacillus Genomics and Metabolic Engineering
- Viruses of Microorganisms
- Protozoan Parasitism
- Genes, Genetics and Transgenics for Virus Resistance in Plants
- DNA Tumour Viruses
- Pathogenic Escherichia coli
- Postgraduate Handbook
- Molecular Biology of Kinetoplastid Parasites
- Bacterial Evasion of the Host Immune System
- Illustrated Dictionary of Parasitology in the Post-Genomic Era
- Next-generation Sequencing and Bioinformatics for Plant Science
- The CRISPR/Cas System
- Brewing Microbiology
- Brain-eating Amoebae
- Foot-and-Mouth Disease Virus
- Microbial Biodegradation
- MALDI-TOF Mass Spectrometry in Microbiology
- Aspergillus and Penicillium in the Post-genomic Era
- The Bacteriocins
- Omics in Plant Disease Resistance
- Climate Change and Microbial Ecology