Increased Sensitivity of the Microbiological Assay for Biotin by Lactobacillus plantarum

Addition of Tween 80 to biotin assay medium containing acid-hydrolyzed casein as the amino acid source caused marked growth of Lactobacillus plantarum ATCC 8014 in the absence of added biotin. This growth-promoting activity could be eliminated by treating the "vitamin-free" Casamino Acids (Difco) with activated charcoal (Darco G-60) at pH 3.5 for 30 to 60 min. Incorporation of Tween 80 and charcoal-purified Casamino Acids (PCA) into the assay medium (0.8 g and 27 g, respectively, per liter of single strength medium) in place of unpurified Casamino Acids resulted in a medium in which L. plantarum responded to 30 to 50 times less biotin over an extended linear response range (1.3 logs versus 1.0 log) than was required for similar growth in the standard medium. Endogenous growth in the modified medium was absent if the inoculum used was of low density, if it was prepared from biotin-deficient cells, and if the reagents used were free from contaminating traces of biotin. Assays of biological materials for biotin content using the standard medium and the Tween 80-PCA-modified medium resulted in nearly identical values for all samples tested.     

Mutation and Selection of Lactobacillus plantarum Strains That Do Not Produce Carbon Dioxide from Malate

A differential medium was developed to distinguish between malate-decarboxylating (MDC⁺) and -non-decarboxylating (MDC⁻) strains of Lactobacillus plantarum. MDC⁻ strains produced a visible acid reaction in the medium, whereas MDC⁺ strains did not. Use of the medium allowed for rapid screening and isolation of mutagenized cells that had lost the ability to produce CO₂ from malate.     

Kinetics and Modeling of Lactic Acid Production by Lactobacillus plantarum

An unstructured model was developed to describe bacterial growth, substrate utilization, and lactic acid production by Lactobacillus plantarum in cucumber juice. Significant lactic acid production occurred during growth, as well as stationary phases. The percentage of acid produced after growth ceased was a function of the medium composition. Up to 51% of the lactic acid was produced after growth ceased when NaCl was not present in the medium, whereas not more than 18% of the total lactic acid was produced after the growth ceased in presence of NaCl, probably because of an increase in the cell death rate. An equation relating the specific death rate and NaCl concentration was developed. With the kinetic model proposed by R. Luedeking and E. L. Piret (J. Biochem. Microbiol. Technol. Eng. 1:393-412, 1958) for lactic acid production rate, the growth-associated and non-growth-associated coefficients were determined as 51.9 (±4.2) mmol/g of cells and 7.2 (±0.9) mmol/g of cells h^-1 respectively. The model was demonstrated for batch growth of L. plantarum in cucumber juice. Mathematical simulations were used to predict the influence of variations in death rate, proton concentration when growth ceased, and buffer capacity of the juice on the overall fermentation process.     

Exopolysaccharides produced by Lactobacillus plantarum: technological properties,biological activity,and potential application in the food industry

Some lactic acid bacteria are capable of producing capsular or extracellular polysaccharides, with desirable technological properties and biological activities. Such polysaccharides produced by lactic acid bacteria are called exopolysaccharides and can be used to alter rheological properties, acting in processes involving viscosity, emulsification, and flocculation, among others. They may also be involved in prebiotic, probiotic, and biological activities, as well as having potential application in the food industry. In this mini-review, the objectives were to present some beneficial properties of exopolysaccharides (EPS) produced by Lactobacillus plantarum that have not been commercially explored. For that, the article focused to summarize revision of current publications within the following topics: (1) rheological properties, (2) prebiotic properties, (3) biological activities, and (4) potential application in the food industry. EPS produced by Lb. plantarum can be used as gelling agent, emulsifier, or stabilizer for food products. The glucan nature of the produced EPS enhances probiotic properties of this LAB species. Lactobacillus plantarum EPS has antioxidant, antibiofilm, and antitumor activities. Finally, there is an improvement in texture of fermented food products where Lb. plantarum is used as starter culture which is related to EPS production in situ. Therefore, EPS produced by Lb. plantarum have important and desirable properties to be explored for several applications, including health and food areas.     

Production and characterization of antifungal compounds produced by Lactobacillus plantarum IMAU10014

Lactobacillus plantarum IMAU10014 was isolated from koumiss that produces a broad spectrum of antifungal compounds, all of which were active against plant pathogenic fungi in an agar plate assay. Two major antifungal compounds were extracted from the cell-free supernatant broth of L. plantarum IMAU10014. 3-phenyllactic acid and Benzeneacetic acid, 2-propenyl ester were carried out by HPLC, LC-MS, GC-MS, NMR analysis. It is the first report that lactic acid bacteria produce antifungal Benzeneacetic acid, 2-propenyl ester. Of these, the antifungal products also have a broad spectrum of antifungal activity, namely against Botrytis cinerea, Glomerella cingulate, Phytophthora drechsleri Tucker, Penicillium citrinum, Penicillium digitatum and Fusarium oxysporum, which was identified by the overlay and well-diffusion assay. F. oxysporum, P. citrinum and P. drechsleri Tucker were the most sensitive among molds.     

Enhancing the Viability of Lactobacillus plantarum Inoculum by Immobilizing the Cells in Calcium-Alginate Beads Incorporating Cryoprotectants

Many literature reports have cited the importance of the rehydration conditions of lyophilized cultures in determining viability. The rate of rehydration and the volume of fluid used have been identified as two important factors. One possible means of controlling these is by immobilizing the cells before lyophilization within a gel matrix in which the subsequent rehydration rate and fluid volume would be controlled by the properties of the gel. In this study Lactobacillus plantarum was immobilized and lyophilized in Ca-alginate beads in which 1 M glycerol or 0.75 M adonitol with skim milk were incorporated as a cryoprotectant. The properties of these Ca-alginate beads were examined before and after lyophilization and rehydration. The beads incorporating glycerol were smaller and stronger than those with adonitol. After lyophilization, size decreased and strength increased but to a greater extent in the beads with glycerol, indicating that the microenvironment within the two bead types was probably different. The protective effect of the bead microenvironment on immobilized L. plantarum was also examined. Lyophilization and rehydration within the alginate beads with either polyol yielded higher survival rates than that attained with free cell cultures during rehydration in optimal or suboptimal conditions. During rehydration under suboptimal conditions, the immobilized cell survival was greatest when 0.75 M adonitol was the incorporated cryoprotectant.     

植物乳杆菌DY6主要抑菌代谢物的分析和鉴定

【背景】被广泛应用于食品和饲料等多个行业的乳酸菌已成为制作生物防腐剂的研究热点。【目的】探究抑菌性能良好的植物乳杆菌DY6的抑菌物质,为其进一步应用提供参考依据。【方法】对植物乳杆菌发酵液中抑菌物质的理化特性进行研究,采用GC-MS分析发酵上清液代谢物,通过多元统计学分析方法推测主要抑菌物质,抑菌物质通过半制备进行初步分离后用GC-MS鉴定。【结果】植物乳杆菌DY6对金黄色葡萄球菌、大肠杆菌、沙门氏菌都有较强的抑制作用。采用不同发酵时间的发酵液作为研究对象,测定发酵上清液的抑菌能力,发酵0-4 h上清液无抑菌能力,发酵至8 h抑菌能力逐步上升,发酵24-48 h发酵上清液抑菌能力趋于稳定,在48 h时抑菌能力最佳,抑菌直径为15.28mm。通过多元统计学分析乳酸菌发酵液差异标志物,发现主要差异物为有机酸(如乳酸、乙酸、丙酸等)和脂肪酸(如辛酸、癸酸等)。经过半制备液相分离发酵上清液得到的抑菌组分,主要有有机酸(如乳酸、乙酸、3-苯基乳酸、苯丙酸等)和脂肪酸(如癸酸、辛酸、壬酸等),另外还有少量的醛类和醇类物质。【结论】确定了植物乳杆菌DY6的抑菌物质主要为有机酸和脂肪酸,为其进一步防腐应用提供了理论基础。     

Water Stress and Day-To-Day Variation in Apparent Photosynthetic Acclimation of Field-Grown Soybeans to Elevated Carbon Dioxide Concentration

Midday measurements of single leaf gas exchange rates of upper canopy leaves of soybeans grown in the field at 350 (AC) and 700 (EC) µmol(CO₂) mol^–1 in open topped chambers sometimes indicated up to 50 % higher net photosynthetic rates (P _N) measured at EC in plants grown at AC compared to EC. On other days mean P _N were nearly identical in the two growth [CO₂] treatments. There was no seasonal pattern to the variable photosynthetic responses of soybean to growth [CO₂]. Even on days with significantly lower P _N in the plants grown at EC, there was no reduction in ribulose-1,5-bisphosphate carboxylase/oxygenase, chlorophyll, or soluble protein contents per unit of leaf area. Over three years, gas exchange evidence of acclimation occurred on days when either soil was dry or the water vapor pressure deficit was high (n = 12 d) and did not occur on days after rain or on days with low water vapor pressure deficit (n = 9 d). On days when photosynthetic acclimation was evident, midday leaf water potentials were consistently 0.2 to 0.3 MPa lower for the plants grown at EC than at AC. This suggested that greater susceptibility to water stress in plants grown at EC cause the apparent photosynthetic acclimation. In other experiments, plants were grown in well-watered pots in field chambers and removed to the laboratory early in the morning for gas exchange measurements. In these experiments, the amount of photosynthetic acclimation evident in the gas exchange measurements increased with the maximum water vapor pressure deficit on the day prior to the measurements, indicating a lag in the recovery of photosynthesis from water stress. The apparent increase in susceptibility to water stress in soybean plants grown at EC is opposite to that observed in some other species, where photosynthetic acclimation was evident under wet but not dry conditions, and may be related to the observation that hydraulic conductance is reduced in soybeans when grown at EC. The day-to-day variation in photosynthetic acclimation observed here may account for some of the conflicting results in the literature concerning the existence of acclimation to EC in field-grown plants.     

Physiological and Biochemical Characteristics of Sugar Beet Plants Grown at an Increased Carbon Dioxide Concentration and at Various Nitrate Doses

Three-week-old sugar beet (Beta vulgaris L.) seedlings were grown for an additional four weeks under controlled conditions: in river sand watered with a modified Knop mixture containing one half-fold (0.5N), standard (1N), and or threefold (3N) nitrate amount, at the irradiance of 90 W/m² PAR, and at the carbon dioxide concentrations of 0.035% (1C treatment) or 0.07% (2C treatment). The increase in the carbon dioxide concentration and in the nitrogen dose resulted in an increase in the leaf area and the leaf and root dry weight per plant. With the increase in the nitrogen dose, morphological indices characterizing leaf growth increased more noticeably in 1C plants than in 2C plants. And vice versa, the effects of increased CO₂ concentration were reduced with the increase in the nitrogen dose. Roots responded to the changes in the CO₂ and nitrate concentrations otherwise than leaves. At a standard nitrate dose (1N), the contents of proteins and nonstructural carbohydrates (sucrose and starch) in leaves depended little on the CO₂ concentration. At a double CO₂ concentration, the content of chlorophyll somewhat decreased, and the net photosynthesis rate (P _n) calculated per leaf area unit increased. An increase in the nitrogen dose did not affect the leaf carbohydrate content of the 1C and 2C plants except the leaves of the 2C-3N plants, where the carbohydrate content decreased. In 1C and 2C plants, an increase in the nitrogen dose caused an increase in the protein and chlorophyll content. Specific P _n values somewhat decreased in 1C-0.5N plants and had hardly any dependence on the nitrate dose in the 2C plants. The carbohydrate content in roots did not depend on the CO₂ concentration, and the content was the highest at 0.5N. Characteristic nitrogen dose-independent acclimation of photosynthesis to an increased carbon dioxide concentration, which was postulated previously [1], was not observed in our experiments with sugar beet grown at doubled carbon dioxide concentration.     

Production, purification and structural characterization of an exopolysaccharide produced by a probiotic Lactobacillus plantarum MTCC 9510

Exopolysaccharides (EPS) from lactic acid bacteria contribute to specific rheology and texture of fermented milk products and finds applications even in non-dairy foods and in therapeutics. Box-Behnken model of response surface methodology (RSM) was employed to formulate the production medium for exopolysaccharide (EPS). FT-IR spectral analysis of the purified EPS from Lactobacillus plantarum MTCC 9510 revealed prominent characteristic groups corresponding to polyhydric alcohols. The degradation temperature (Td) of the polysaccharide was found to be 260°C with the help of thermo gravimetric analysis (TGA). Structure elucidation of the EPS showed that it consists of a trisaccharide repeating unit of α-d-glucose, β-d-glucose and α-d-mannose.     

Increased Production of Hydrogen Peroxide by Lactobacillus delbrueckii subsp. bulgaricus upon Aeration: Involvement of an NADH Oxidase in Oxidative Stress

The growth of Lactobacillus delbrueckii subsp. bulgaricus (L. delbrueckii subsp. bulgaricus) on lactose was altered upon aerating the cultures by agitation. Aeration caused the bacteria to enter early into stationary phase, thus reducing markedly the biomass production but without modifying the maximum growth rate. The early entry into stationary phase of aerated cultures was probably related to the accumulation of hydrogen peroxide in the medium. Indeed, the concentration of hydrogen peroxide in aerated cultures was two to three times higher than in unaerated ones. Also, a similar shift from exponential to stationary phase could be induced in unaerated cultures by adding increasing concentrations of hydrogen peroxide. A significant fraction of the hydrogen peroxide produced by L. delbrueckii subsp. bulgaricus originated from the reduction of molecular oxygen by NADH catalyzed by an NADH:H₂O₂ oxidase. The specific activity of this NADH oxidase was the same in aerated and unaerated cultures, suggesting that the amount of this enzyme was not directly regulated by oxygen. Aeration did not change the homolactic character of lactose fermentation by L. delbrueckii subsp. bulgaricus and most of the NADH was reoxidized by lactate dehydrogenase with pyruvate. This indicated that NADH oxidase had no (or a very small) energetic role and could be involved in eliminating oxygen.     

Hot-Loop Test for the Determination of Carbon Dioxide Production from Glucose by Lactic Acid Bacteria

A hot-loop test was found to be more rapid, convenient, and reliable for the detection of carbon dioxide production than were conventional methods such as displacement of agar plugs and precipitation in barium hydroxide.     

Gas Exchange of Algae: III. Relation between the Concentration of Carbon Dioxide in the Nutrient Medium and the Oxygen Production of Chlorella pyrenoidosa

The oxygen production of a photosynthetic gas exchanger containing Chlorella pyrenoidosa (1% packed cell volume) was measured when various concentrations of carbon dioxide were present within the culture unit. The internal carbon dioxide concentrations were obtained by manipulating the entrance gas concentration and the flow rate. Carbon dioxide percentages were monitored by means of electrodes placed directly in the nutrient medium. The concentration of carbon dioxide in the nutrient medium which produced maximal photosynthesis was in the range of 1.5 to 2.5% by volume. Results were unaffected by either the level of carbon dioxide in the entrance gas or the rate of gas flow. Entrance gases containing 2% carbon dioxide flowing at 320 ml/min, 3% carbon dioxide at 135 ml/min, and 4% carbon dioxide at 55 ml/min yielded optimal carbon dioxide concentrations in the particular unit studied. By using carbon dioxide electrodes implanted directly in the gas exchanger to optimize the carbon dioxide concentration throughout the culture medium, it should be possible to design more efficient large-scale units.     

Production of plantaricin NC8 by Lactobacillus plantarum NC8 is induced in the presence of different types of gram-positive bacteria

Lactobacillus plantarum NC8 was shown to produce plantaricin NC8 (PLNC8), a recently purified and genetically characterized inducible class IIb bacteriocin, only when it was co-cultured with other gram-positive bacteria. Among 82 strains belonging to the genera Bacillus, Enterococcus, Lactobacillus, Lactococcus, Leuconostoc, Listeria, Pediococcus, Staphylococcus, and Streptococcus, 41 were shown to induce PLNC8 production in L. plantarum NC8. There was apparently no relationship between the sensitivity of the strains and their ability to induce the bacteriocin, indicating that the inducer and sensitive phenotypes may not be linked. In some instances, induction was promoted by both living and heat-killed cells of the inducing bacteria. However, no PLNC8-inducing activity was found in the respective cell-free, pure culture supernatants. Inducer strains also promoted the production of a PLNC8-autoinducing activity by L. plantarum NC8, which was found only in the cell-free co-culture supernatants showing inhibitory activity. This PLNC8-autoinducing activity was diffusible, heat resistant, and of a proteinaceous nature, and was different from the bacteriocin itself. Taken together, the results suggest that the presence of specific gram-positive bacteria acts as an environmental stimulus activating both PLNC8 production by L. plantarum NC8 and a PLNC8-autoinducing activity, which in turn triggers or maintains bacteriocin production in the absence of inducing cells.     

Comparative studies of the degradation of grass fructan and inulin by strains of Lactobacillus paracasei subsp. paracasei and Lactobacillus plantarum

Four strains of Lactobacillus paracasei subsp. paracasei and Lact. plantarum are investigated within 16 d in order to determine the formation of metabolites during the degradation of grass fructan and inulin as well as the subsequent fermentation to lactic acid. The decrease of the total content of fructans throughout the entire time of investigation shows differences specific for strains as for either fructan substrate. The strain Lact. plantarum V 54/6 completely degrades the grass fructan and inulin within no longer than 13 d. The utilization of fructan by the other strains is temporally delayed, and in a smaller degree of degradation, especially remarkable for inulin cleavage. The structural modifications of decomposed fructans are characterized by a noticeable shift of the mean DP from approximately 80 to the oligomeric range analysed by anion exchange chromatography. Additionally, a newly formed series of peaks of oligomeric saccharides was detected during the degradation of grass fructan and inulin. Part of the fructose that is derived from cleavage of fructans is fermented immediately by the LAB strains into differently high amounts of lactic acid. The abundance of formed fructose is enriched in the medium to a varying extent, depending on the strain as well as the substrate used. From these results a number of fructan degradative enzymes in lactobacilli have been concluded to possibly vary their modes of regulation: strain specific exo- and endohydrolases with different activities against β-2,1 and β-2,6 linked fructan.