High cell density cultivation of probiotics and lactic acid production

Probiotic characterization of Bacillus smithii: Research advances, concerns, and prospective trends

Bacillus smithii is a thermophilic Bacillus that can be isolated from white wine, hot spring soil, high-temperature compost, and coffee grounds, with various biofunctions and wide applications. It is resistant to both gastric acid and high temperature, which makes it easier to perform probiotic effects than traditional commercial probiotics, so it can maintain good vitality during food processing and has great application prospects. This paper starts with the taxonomy and genetics and focuses on aspects, including genetic transformation, functional enzyme production, waste utilization, and application in the field of food science as a potential probiotic. According to available studies during the past 30 years, we considered that B. smithii is a novel class of microorganisms with a wide range of functional enzymes such as hydrolytic enzymes and hydrolases, as well as resistance to pathogenic bacteria. It is available in waste degradation, organic fertilizer production, the feed and chemical industries, the pharmaceutical sector, and food fortification. Moreover, B. smithii has great potentials for applications in the food industry, as it presents high resistance to the technological processes that guarantee its health benefits. It is also necessary to systematically evaluate the safety, flavor, and texture of B. smithii and explore its biological mechanism of action, which is of great value for further application in multiple fields, especially in food and medicine.

Role of Clay Substrate Molecular Interactions in Some Dairy Technology Applications

The use of clay materials in dairy technology requires a multidisciplinary approach that allows correlating clay efficiency in the targeted application to its interactions with milk components. For profitability reasons, natural clays and clay minerals can be used as low-cost and harmless food-compatible materials for improving key processes such as fermentation and coagulation. Under chemical stability conditions, clay materials can act as adsorbents, since anionic clay minerals such as hydrotalcite already showed effectiveness in the continuous removal of lactic acid via in situ anion exchange during fermentation and ex situ regeneration by ozone. Raw and modified bentonites and smectites have also been used as adsorbents in aflatoxin retention and as acidic species in milk acidification and coagulation. Aflatoxins and organophilic milk components, particularly non-charged caseins around their isoelectric points, are expected to display high affinity towards high silica regions on the clay surface. Here, clay interactions with milk components are key factors that govern adsorption and surface physicochemical processes. Knowledge about these interactions and changes in clay behavior according to the pH and chemical composition of the liquid media and, more importantly, clay chemical stability is an essential requirement for understanding process improvements in dairy technology, both upstream and downstream of milk production. The present paper provides a comprehensive review with deep analysis and synthesis of the main findings of studies in this area. This may be greatly useful for mastering milk processing efficiency and envisaging new prospects in dairy technology.

Analysis of the effects of specific growth rate of Lactococcus lactis MG1363 on aerobic metabolism and its application to high-density culture

Lactic acid bacteria (LAB) are known to produce a large amount of lactate when cultured under non-aerated conditions, which inhibits their growth at high concentrations. Our previous studies have shown that LAB can be cultured without lactate production under aerated conditions at a low specific growth rate. In this study, we investigated the effects of specific growth rate on cell yield and the specific production rates of metabolites in aerated fed-batch cultures of Lactococcus lactis MG1363. The results showed that lactate and acetoin production could be suppressed at specific growth rates below 0.2 h^-1, whereas acetate production was the highest at a specific growth rate of 0.2 h^-1. When LAB was cultured at a specific growth rate of 0.25 h^-1 with the addition of 5 mg/L heme to assist ATP production by respiration, lactate and acetate production was suppressed, and cell concentration reached 19 g-dry-cell/L (5.6 × 10ˆ10 cfu/mL) with a high cell yield of 0.42 ± 0.02 g-dry-cell/g-glucose.

Journey of the Probiotic Bacteria: Survival of the Fittest

This review aims to bring a more general view of the technological and biological challenges regarding production and use of probiotic bacteria in promoting human health. After a brief description of the current concepts, the challenges for the production at an industrial level are presented from the physiology of the central metabolism to the ability to face the main forms of stress in the industrial process. Once produced, these cells are processed to be commercialized in suspension or dried forms or added to food matrices. At this stage, the maintenance of cell viability and vitality is of paramount for the quality of the product. Powder products requires the development of strategies that ensure the integrity of components and cellular functions that allow complete recovery of cells at the time of consumption. Finally, once consumed, probiotic cells must face a very powerful set of physicochemical mechanisms within the body, which include enzymes, antibacterial molecules and sudden changes in pH. Understanding the action of these agents and the induction of cellular tolerance mechanisms is fundamental for the selection of increasingly efficient strains in order to survive from production to colonization of the intestinal tract and to promote the desired health benefits.

Effect of Trehalose and Lactose Treatments on the Freeze-Drying Resistance of Lactic Acid Bacteria in High-Density Culture

Freeze-drying is a commonly used method in commercial preparations of lactic acid bacteria. However, some bacteria are killed during the freeze-drying process. To overcome this, trehalose and lactose are often used as protective agents. Moreover, high-density culture is an efficient way to grow bacterial strains but creates a hypertonic growth environment. We evaluated the effects of trehalose and lactose, as a primary carbon source or as an additive in fermentation, on the freeze-drying survival of Lactobacillus fermentum FXJCJ6-1, Lactobacillus brevis 173-1-2, and Lactobacillus reuteri CCFM1040. Our results showed that L. fermentum FXJCJ6-1 accumulated but did not use intracellular trehalose in a hypertonic environment, which enhanced its freeze-drying resistance. Furthermore, genes that could transport trehalose were identified in this bacterium. In addition, both the lactose addition and lactose culture improved the freeze-drying survival of the bacterium. Further studies revealed that the added lactose might exert its protective effect by attaching to the cell surface, whereas lactose culture acted by reducing extracellular polysaccharide production and promoting the binding of the protectant to the cell membrane. The different mechanisms of lactose and trehalose in enhancing the freeze-drying resistance of bacteria identified in this study will help to elucidate the anti-freeze-drying mechanisms of other sugars in subsequent investigations.

Clay-Catalyzed Ozonation of Hydrotalcite-Extracted Lactic Acid Potential Application for Preventing Milk Fermentation Inhibition

An unprecedented route for mitigating the inhibitory effect of lactic acid (LA) on milk fermentation was achieved through lactate adsorption on hydrotalcite (Ht) from simulated lactate extracts. During its regeneration by ozonation, Ht displayed catalytic activity that appeared to increase by addition of montmorillonite (Mt). Changes in the pH, Zeta potential and catalyst particle size during LA ozonation were found to strongly influence LA–LA, LA–catalyst and catalyst–catalyst interactions. The latter determine lactate protonation–deprotonation and clay dispersion in aqueous media. The activity of Mt appears to involve hydrophobic adsorption of non-dissociated LA molecules on silica-rich areas at low pH, and Lewis acid–base and electrostatic interactions at higher pH than the pKa. Hydrotalcite promotes both hydrophobic interaction and anion exchange. Hydrotalcite–smectite mixture was found to enhance clay dispersion and catalytic activity. This research allowed demonstrating that natural clay minerals can act both as adsorbents for LA extract from fermentation broths and as catalysts for adsorbent regeneration. The results obtained herein provide valuable and useful findings for envisaging seed-free milk clotting in dairy technologies.

Safety evaluation of Lactococcus lactis IDCC 2301 isolated from homemade cheese

For applications of microorganisms as probiotics in the food industry, safety evaluation has increasingly become important to ensure the health of consumers. Although people have been using various lactic acid bacteria for different purposes, some studies have reported that certain lactic acid bacteria exhibit properties of virulence and produce toxic compounds. Thus, it is necessary to examine the characteristics associated with lactic acid bacteria that are safe for use as probiotics. This research aimed to assess the safety of Lactococcus lactis IDCC 2301 isolated from homemade cheese using in vitro and in vivo assays, including antibiotic resistance, hemolytic activity, toxin production, infectivity, and metabolic activity in immune-compromised animal species. The results demonstrated that the strain was susceptible to nine antibiotics suggested by the European Food Safety Authority (EFSA). Whole-genome analysis revealed that L. lactis IDCC 2301 neither has toxigenic genes nor harbors antibiotic resistance. Moreover, L. lactis IDCC 2301 showed neither hemolytic nor β-glucuronidase activity. Furthermore, none of the D-lactate and biogenic amines were produced by L. lactis IDCC 2301. Finally, it was demonstrated that there was no toxicity and mortality using single-dose oral toxicity tests in rats. These results indicate that L. lactis IDCC 2301 can be safely used as probiotics for human consumption.

Safety assessment of Streptococcus thermophilus IDCC 2201 used for product manufacturing in Korea

Safety evaluation of probiotics has become increasingly important for human consumption in food industry. The aims of this study were to assess safety of Streptococcus thermophilus IDCC 2201 through in vitro and in vivo tests. In results, this strain was found to be negative for hemolytic and β-glucuronidase activity. In addition, thermophilus IDCC 2201 was susceptible to nine antibiotics suggested by EFSA. In accordance with MIC tests, whole-genome analysis indicated that S. thermophilus IDCC 2201 neither harbors antibiotic resistance nor toxigenic genes. Furthermore, none of the biogenic amines including tyramine and histamine was produced and negligible amounts of D-lactate were produced by S. thermophilus IDCC 2201. Finally, it was confirmed that there was no mortality and toxicity throughout single-dose oral toxicity tests in rats. Therefore, we report that S. thermophilus IDCC 2201 is considered to be safe for human consumption as probiotics.

Ionic Liquids Toxicity-Benefits and Threats

Ionic liquids (ILs) are solvents with salt structures. Typically, they contain organic cations (ammonium, imidazolium, pyridinium, piperidinium or pyrrolidinium), and halogen, fluorinated or organic anions. While ILs are considered to be environmentally-friendly compounds, only a few reasons support this claim. This is because of high thermal stability, and negligible pressure at room temperature which makes them non-volatile, therefore preventing the release of ILs into the atmosphere. The expansion of the range of applications of ILs in many chemical industry fields has led to a growing threat of contamination of the aquatic and terrestrial environments by these compounds. As the possibility of the release of ILs into the environment s grow systematically, there is an increasing and urgent obligation to determine their toxic and antimicrobial influence on the environment. Many bioassays were carried out to evaluate the (eco)toxicity and biodegradability of ILs. Most of them have questioned their "green" features as ILs turned out to be toxic towards organisms from varied trophic levels. Therefore, there is a need for a new biodegradable, less toxic "greener" ILs. This review presents the potential risks to the environment linked to the application of ILs. These are the following: cytotoxicity evaluated by the use of human cells, toxicity manifesting in aqueous and terrestrial environments. The studies proving the relation between structures versus toxicity for ILs with special emphasis on directions suitable for designing safer ILs synthesized from renewable sources are also presented. The representants of a new generation of easily biodegradable ILs derivatives of amino acids, sugars, choline, and bicyclic monoterpene moiety are collected. Some benefits of using ILs in medicine, agriculture, and the bio-processing industry are also presented.

Lactobacillus brevis CD2: Fermentation Strategies and Extracellular Metabolites Characterization

Functional foods and nutraceuticals frequently contain viable probiotic strains that, at certain titers, are considered to be responsible of beneficial effects on health. Recently, it was observed that secreted metabolites might play a key role in this respect, especially in immunomodulation. Exopolysaccharides produced by probiotics, for example, are used in the food, pharmaceutical, and biomedical fields, due to their unique properties. Lactobacillus brevis CD2 demonstrated the ability to inhibit oral pathogens causing mucositis and periodontal inflammation and to reduce Helycobacter pylori infections. Due to the lack of literature, for this strain, on the development of fermentation processes that can increase the titer of viable cells and associated metabolites to industrially attractive levels, different batch and fed-batch strategies were investigated in the present study. In particular, aeration was shown to improve the growth rate and the yields of lactic acid and biomass in batch cultures. The use of an exponential feeding profile in fed-batch experiments allowed to produce 9.3 ± 0.45 × 10⁹ CFU/mL in 42 h of growth, corresponding to a 20-fold increase of viable cells compared with that obtained in aerated batch processes; moreover, also increased titers of exopolysaccharides and lactic acid (260 and 150%, respectively) were observed. A purification process based on ultrafiltration, charcoal treatment, and solvent precipitation was applied to partially purify secreted metabolites and separate them into two molecular weight fractions (above and below 10 kDa). Both fractions inhibited growth of the known gut pathogen, Salmonella typhimurium, demonstrating that lactic acid plays a major role in pathogen growth inhibition, which is however further enhanced by the presence of Lact. brevis CD2 exopolysaccharides. Finally, the EPS produced from Lact. brevis CD2 was characterized by NMR for the first time up to date.

Multi-Product Lactic Acid Bacteria Fermentations: A Review

Industrial biotechnology is a continuously expanding field focused on the application of microorganisms to produce chemicals using renewable sources as substrates. Currently, an increasing interest in new versatile processes, able to utilize a variety of substrates to obtain diverse products, can be observed. A robust microbial strain is critical in the creation of such processes. Lactic acid bacteria (LAB) are used to produce a wide variety of chemicals with high commercial interest. Lactic acid (LA) is the most predominant industrial product obtained from LAB fermentations, and its production is forecasted to rise as the result of the increasing demand of polylactic acid. Hence, the creation of new ways to revalorize LA production processes is of high interest and could further enhance its economic value. Therefore, this review explores some co-products of LA fermentations, derived from LAB, with special focus on bacteriocins, lipoteichoic acid, and probiotics. Finally, a multi-product process involving LA and the other compounds of interest is proposed.

Lactobacillus plantarum LMT1-48 exerts anti-obesity effect in high-fat diet-induced obese mice by regulating expression of lipogenic genes

Obesity is a major health problem and is known to be closely associated with metabolic diseases. Abnormal hepatic accumulation of fat causes fatty liver or hepatic steatosis, and long-term consumption of a high-fat diet is known to be a key obesity-causing factor. Recent studies have demonstrated that probiotics such as Lactobacillus strains, exert an anti-obesity effect by regulating adipogenesis. However, it is still unknown how the consumption of probiotics can reduce abdominal fat volume by regulating the hepatic expression of lipogenic genes. Therefore, we evaluated the effect of long-term ingestion of L. plantarum LMT1-48 on the expression of lipogenic genes in high-fat diet (HFD)-fed mice. We observed that treatment of 3T3-L1 adipocytes with L. plantarum LMT1-48 extract inhibited their differentiation and lipid accumulation by downregulating lipogenic genes, namely, PPARγ, C/EBPα, FAS, and FABP4. Interestingly, administration of L. plantarum LMT1-48 reduced liver weight and liver triglycerides concurrently with the downregulation of the lipogenic genes PPARγ, HSL, SCD-1, and FAT/CD36 in the liver, resulting in the reduction of body weight and fat volume in HFD-fed obese mice. Notably, we also observed that the administration of at least 10⁶ CFU of L. plantarum LMT1-48 significantly lowered body weight and abdominal fat volume in modified diet-fed mouse models. Collectively, these data suggest that L. plantarum LMT1-48 is a potential healthy food for obese people.

Improvement of the antimicrobial activity of lactic acid bacteria in combination with berries/fruits and dairy industry by-products

BACKGROUND

By-products from berries/fruits (B/F) and the dairy industry (DI) are an important environmental issue in many countries. In the present study, the concept of an improvement of the antimicrobial activity of lactic acid bacteria (LAB) in combination with B/F (raspberries, blackcurrants, apples, rowanberries) and DI by-products was analysed. Antimicrobial activities of the B/F by-products and LAB (13 LAB strains were estimated against 15 pathogenic strains) were evaluated, with whey substrate being used for the selected and the highest antimicrobial activities showing LAB cultivation.

RESULTS

The broadest spectrum of pathogenic bacteria inhibition was shown by lyophilised blackcurrant and apple by-products, which inhibited 13 and 12 pathogenic strains of the 15 strains analysed, respectively. The strongest inhibition of the tested pathogens were shown by the Lactobacillus uvarum LUHS245 and Lactobacillus casei LUHS210 and, for the abovementioned LAB biomass preparation, whey enriched with 2.5 g 100 g^-1 glucose, 2.0 g 100 g^-1 yeast extract and 0.5 g 100 g^-1 saccharose is a suitable and sustainable substrate. The B/F by-product's antimicrobial activity can be enhanced in combination with the LUHS245 and LUHS210 strains.

CONCLUSION

LAB, B/F and DI by-products can be used for preparation of antimicrobial products because the combination of compounds from different origins showed higher antimicrobial properties. © 2019 Society of Chemical Industry.

Effects of nanobubble water on the growth ofLactobacillus acidophilus1028 and its lactic acid production

Nanobubbles (NBs) in the culture medium may offer a new way of accelerating bacterial growth in the lag and logarithmic phases.

Extractive Fermentation of Lactic Acid in Lactic Acid Bacteria Cultivation: A Review

Lactic acid bacteria are industrially important microorganisms recognized for their fermentative ability mostly in their probiotic benefits as well as lactic acid production for various applications. Nevertheless, lactic acid fermentation often suffers end-product inhibition which decreases the cell growth rate. The inhibition of lactic acid is due to the solubility of the undissociated lactic acid within the cytoplasmic membrane and insolubility of dissociated lactate, which causes acidification of cytoplasm and failure of proton motive forces. This phenomenon influences the transmembrane pH gradient and decreases the amount of energy available for cell growth. In general, the restriction imposed by lactic acid on its fermentation can be avoided by extractive fermentation techniques, which can also be exploited for product recovery.

A membrane stirrer for product recovery and substrate feeding

During fermentation processes, in situ product recovery (ISPR) using submerged membranes allows a continuous operation mode with effective product removal. Continuous recovery reduces product inhibition and organisms in the reactor are not exposed to changing reaction conditions. For an effective in situ product removal, submerged membrane systems should have a sufficient large membrane area and an anti-fouling concept integrated in a compact device for the limited space in a lab-scale bioreactor. We present a new membrane stirrer with integrated filtration membranes on the impeller blades as well as an integrated gassing concept in an all-in-one device. The stirrer is fabricated by rapid prototyping and is equipped with a commercial micromesh membrane. Filtration performance is tested using a yeast cell suspension with different stirring speeds and aeration fluxes. We reduce membrane fouling by backflushing through the membrane with the product stream.

Improvement of the fermentative activity of lactic acid bacteria starter culture by the addition of Mn²⁺

Production of lactic acid bacteria (LAB) starter with raw material has received much scientific investigation, but little information is available on the influences of some trace elements on the growth and fermentative activity of LAB. Based on this fact, this paper aimed to investigate the effects of Mn(2+) on the performance of Lactobacillus plantarum CX-15 starter with Jerusalem artichoke (JA) as the main medium substrate. The results showed that Mn(2+) addition had a significant beneficial affect on the fermentative activity of L. plantarum CX-15 starter. In contrast, the lack of Mn(2+) would cause the subsequent fermentation significantly slower, whether the cell density in starter culture was higher or lower. The possible mechanism of these phenomenons was further elucidated by the time course analysis of the specific activities of metabolism key enzymes during the culture processes of L. plantarum CX-15 starter. Compared to the fermentation processes without Mn(2+) addition, it was found that Mn(2+) addition would enhance the lactate dehydrogenase (LDH) activity but reduce the activities of pyruvate dehydrogenase (PDH) and ATPase activity. Therefore, it could be concluded that the improvement of L. plantarum starter fermentative activity was probably a consequence of Mn(2+) acting as "metabolic switch," which regulated the metabolic flux from pyruvic acid to lactic acid and other metabolism pathway.

Lactobacillus crispatus L1: high cell density cultivation and exopolysaccharide structure characterization to highlight potentially beneficial effects against vaginal pathogens

BACKGROUND

Vaginal lactic acid bacteria defend the host against pathogens through a combination of competitive exclusion, competition for nutrients, production of antimicrobial substances and through the activation of the immune system. A new human isolate named Lactobacillus crispatus L1 was characterized in this work, and a preliminary evaluation of its probiotic potential is described together with a process to obtain a high productivity of viable biomass.

RESULTS

In a simulated digestion process 1.8⋅10(10) cells∙ml(-1) survived the gastric environment with 80% viability, without being affected by small intestine juices. Experiments on six different C sources were performed to analyze growth and organic acids production and, glucose, provided the best performances. A microfiltration strategy was exploited to improve the cellular yield in 2 L-fermentation processes, reaching 27 g · l(-1) of dry biomass. Moreover, L. crispatus L1 demonstrated a greater stability to high concentrations of lactic acid, compared to other lactobacilli. The specific L. crispatus L1 exopolysaccharide was purified from the fermentation broth and characterized by NMR showing structural features and similarity to exopolysaccharides produced by pathogenic strains. Live L. crispatus L1 cells strongly reduced adhesion of a yeast pathogenic strain, Candida albicans in particular, in adherence assays. Interestingly a higher expression of the human defensin HBD-2 was also observed in vaginal cells treated with the purified exopolysaccharide, indicating a possible correlation with C. albicans growth inhibition.

CONCLUSIONS

The paper describes the evaluation of L. crispatus L1 as potential vaginal probiotic and the fermentation processes to obtain high concentrations of viable cells.

l-(+)-Lactic acid production by co-fermentation of cellobiose and xylose without carbon catabolite repression using Enterococcus mundtii QU 25

We established an effective highl-lactic acid production system based on fed-batch bacterial cultures utilising lignocellulosic biomass-derived mixed sugars without carbon catabolite repression.

Recombinant production of hyperthermostable CelB from Pyrococcus furiosus in Lactobacillus sp

Lactic acid bacteria (LAB) are used widespread in the food industry as traditional starters for various fermented foods. For recombinant protein production, LAB would be superior with view from the food safety demands since most of them are Generally Recognized As Safe organisms. We investigated the two pSIP expression systems, pSIP403 and pSIP409 (Sørvig et al. 2005), to produce a hyper-thermophilic β-glycosidase (CelB) from Pyrococcus furiosus in Lactobacillus plantarum NC8 and Lactobacillus casei as hosts, respectively. Both lactobacilli harboring the pSIP409-celB vector produced active CelB in batch bioreactor cultivations (MRS medium) while the specific CelB activity of the cell free extract was about 44 % higher with L. plantarum (1,590 ± 90 nkat/mg(protein)) than with L. casei (1,070 ± 66 nkat/mg(protein)) using p-nitrophenyl-β-galactoside (pNPGal) as the substrate. A fed-batch bioreactor cultivation of L. plantarum NC8 pSIP409-celB resulted in a specific CelB activity of 2,500 ± 120 nkat ( pNPGal)/mg(protein) after 28 h. A repeated dosage of the inducer spp-IP did not increase the enzyme expression further. As alternative for the cost intensive MRS medium, a basal whey medium with supplements (yeast extract, Tween 80, NH(4)-citrate) was developed. In bioreactor cultivations using this medium, about 556 ± 29 nkat ( pNPGal)/mg(protein) of CelB activity was achieved. It was shown that both LAB were potential expression hosts for recombinant enzyme production. The pSIP expression system can be applied in L. casei.

The complete genome sequence of Lactobacillus bulgaricus reveals extensive and ongoing reductive evolution

Lactobacillus delbrueckii ssp. bulgaricus (L. bulgaricus) is a representative of the group of lactic acid-producing bacteria, mainly known for its worldwide application in yogurt production. The genome sequence of this bacterium has been determined and shows the signs of ongoing specialization, with a substantial number of pseudogenes and incomplete metabolic pathways and relatively few regulatory functions. Several unique features of the L. bulgaricus genome support the hypothesis that the genome is in a phase of rapid evolution. (i) Exceptionally high numbers of rRNA and tRNA genes with regard to genome size may indicate that the L. bulgaricus genome has known a recent phase of important size reduction, in agreement with the observed high frequency of gene inactivation and elimination; (ii) a much higher GC content at codon position 3 than expected on the basis of the overall GC content suggests that the composition of the genome is evolving toward a higher GC content; and (iii) the presence of a 47.5-kbp inverted repeat in the replication termination region, an extremely rare feature in bacterial genomes, may be interpreted as a transient stage in genome evolution. The results indicate the adaptation of L. bulgaricus from a plant-associated habitat to the stable protein and lactose-rich milk environment through the loss of superfluous functions and protocooperation with Streptococcus thermophilus.

Exopolysaccharides production in Lactobacillus bulgaricus and Lactobacillus casei exploiting microfiltration

The physiology of Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus casei, extensively used in the dairy industry, was studied in order to evaluate key parameters in the synthesis of exopolysaccharides and to improve their production through novel fermentation processes. Selected strains were studied in shake flasks and in fermentor experiments using glucose and lactose as main carbon sources and bacto casitone as the only complex component, in a temperature range between 35 and 42 degrees C. The production of exopolysaccharides was monitored and correlated to the growth conditions using both a colorimetric assay and chromatographic methods. Fermentor experiments in batch mode yielded 100 mg l(-1) of EPS from L. bulgaricus and 350 mg l(-1) from L. casei. Moreover, the use of a microfiltration (MF) bioreactor resulted in exopolysaccharides (EPS) concentrations threefold and sixfold those of batch experiments, respectively. The monosaccharidic composition of the two analyzed polymers differed from those previously reported. The optimization of the production of EPSs using the MF fermentation strategy could permit the use of these molecules produced by generally recognised as safe (GRAS) microorganisms in the place of other polysaccharides in the food industry.

10 years of the nisin-controlled gene expression system (NICE) in Lactococcus lactis

Lactococcus lactis is a Gram-positive lactic acid bacterium that, in addition to its traditional use in food fermentations, is increasingly used in modern biotechnological applications. In the last 25 years great progress has been made in the development of genetic engineering tools and the molecular characterization of this species. A new versatile and tightly controlled gene expression system, based on the auto-regulation mechanism of the bacteriocin nisin, was developed 10 years ago-the NIsin Controlled gene Expression system, called NICE. This system has become one of the most successful and widely used tools for regulated gene expression in Gram-positive bacteria. The review describes, after a brief introduction of the host bacterium L. lactis, the fundaments, components and function of the NICE system. Furthermore, an extensive overview is provided of the different applications in lactococci and other Gram-positive bacteria: (1) over-expression of homologous and heterologous genes for functional studies and to obtain large quantities of specific gene products, (2) metabolic engineering, (3) expression of prokaryotic and eukaryotic membrane proteins, (4) protein secretion and anchoring in the cell envelope, (5) expression of genes with toxic products and analysis of essential genes and (6) large-scale applications. Finally, an overview is given of growth and induction conditions for lab-scale and industrial-scale applications.