Diagnosing lactic acid fermentation based on specific rates of growth,substrate consumption and product formation

The on-line calculated specific rates of growth, substrate consumption and product formation were used to diagnose microbial activities during a lactic acid fermentation. The specific rates were calculated from on-line measured cell mass, and substrate and product concentrations. The specific rates were more sensitive indicators of slight changes in fermentation conditions than such monitored data as cell mass or product concentrations.List of Symbols 1/h specific rate of cell growth - 1/h specific rate of substrate consumption - 1/h specific rate of product formation - ^* dimensionless specific rate of cell growth - ^* dimensionless specific rate of substrate consumption - ^* dimensionless specific rate of product formation - _max 1/h maximum specific rate of cell growth - _max 1/h maximum specific rate of substrate consumption - _max 1/h maximum specific rate of product formation - X g/l cell mass concentration - S g/l substrate concentration - S ^* dimensionless substrate concentration - S ₀ g/l initial substrate concentration - P g/l product concentration     

A rapid method for differentiation of dairy lactic acid bacteria by enzyme systems

Summary A rapid and simple technique utilizing the APIZYM enzymatic patterns complemented with arginine dihydrolase and citratase was developed for species differentiation of 40 lactic acid bacteria relevant to the dairy industry.Streptococcus species in general produced no -galactosidase, except forStreptococcus thermophilus. Lactobacillus species showed strong aminopeptidases and galactosidases but contained no arginine dihydrolase and citratase. Among the group N-streptococci,Streptococcus diacetylactis produced citratase, whereasStreptococcus cremoris differed by the production of butyrate esterase.Streptococcus faecalis was readily distinguishable fromStreptococcus lactis by butyrate esterase activity that was the basis of the differential agar developed. Heterofermentative lactobacilli differed from homofermentative lactobacilli in possessing arginine dihydrolase and citratase but by not producing leucine-aminopeptidase.     

Associative growth studies in three-strain mixtures of lactic streptococci

A recently developed differential agar medium was used to study associative growth patterns in 17 different heterologous, three-strain mixtures of Streptococcus lactis, S. cremoris, and S. diacetilactis grown in milk. Mixtures were made by combining equal volumes of 18-hr milk cultures of the three species. Relative populations of component species were followed through three successive transfers in milk after the initial mixed propagation. Direct evidence for strain dominance and compatibility was obtained. A procedure also was developed to estimate the extent of suppression of S. lactis and S. diacetilactis in a mixture containing a dominant S. cremoris strain. The technique described could be successfully applied in quality-control work in the dairy-starter manufacturing industry.     

Simple and rapid method for isolating large plasmid DNA from lactic streptococci.

A procedure for the rapid isolation of plasmid DNA larger than 30 megadaltons from lactic streptococci is described. This protocol can be used on a preparative scale to isolate sufficient quantities of plasmid DNA required for restriction analysis, cloning, or transformation experiments. A scaled-down protocol is very useful for rapidly screening the plasmid content of streptococcal strains. With this methodology, previously undetected large plasmids were observed.     

Use of virginiamycin to control the growth of lactic acid bacteria during alcohol fermentation

The antibiotic virginiamycin was investigated for its effects on growth and lactic acid production by seven strains of lactobacilli during the alcoholic fermentation of wheat mash by yeast. The lowest concentration of virginiamycin tested (0.5 mg Lactrol ^TMkg⁻¹ mash), was effective against most of the lactic acid bacteria under study, but Lactobacillus plantarum was not significantly inhibited at this concentration. The use of virginiamycin prevented or reduced potential yield losses of up to 11% of the produced ethanol due to the growth and metabolism of lactobacilli. However, when the same concentration of virginiamycin was added to mash not inoculated with yeast, Lactobacillus rhamnosus and L. paracasei grew after an extensive lag of 48 h and L. plantarum grew after a similar lag even in the presence of 2 mg virginiamycin kg⁻¹ mash. Results showed a variation in sensitivity to virginiamycin between the different strains tested and also a possible reduction in effectiveness of virginiamycin over prolonged incubation in wheat mash, especially in the absence of yeast. Received 05 August 1996/ Accepted in revised form 18 December 1996     

Improved medium for lactic streptococci and their bacteriophages

[This corrects the article on p. 807 in vol. 29.].     

Improved medium for lactic streptococci and their bacteriophages

Incorporation of 1.9% β-disodium glycerophosphate (GP) into a complex medium resulted in improved growth by lactic streptococci at 30 C. The medium, called M17, contained: Phytone peptone, 5.0 g; polypeptone, 5.0 g; yeast extract, 2.5 g; beef extract, 5.0 g; lactose, 5.0 g; ascorbic acid, 0.5 g; GP, 19.0 g; 1.0 M MgSO₄·7H₂O, 1.0 ml; and glass-distilled water, 1,000 ml. Based on absorbance readings and total counts, all strains of Streptococcus cremoris, S. diacetilactis, and S. lactis grew better in M17 medium than in a similar medium lacking GP or in lactic broth. Enhanced growth was probably due to the increased buffering capacity of the medium, since pH values below 5.70 were not reached after 24 h of growth at 30 C by S. lactis or S. cremoris strains. The medium also proved useful for isolation of bacterial mutants lacking the ability to ferment lactose; such mutants formed minute colonies on M17 agar plates, whereas wild-type cells formed colonies 3 to 4 mm in diameter. Incorporation of sterile GP into skim milk at 1.9% final concentration resulted in enhanced acid-producing activity by lactic streptococci when cells were inoculated from GP milk into skim milk not containing GP. M17 medium also proved superior to other media in demonstrating and distinguishing between lactic streptococcal bacteriophages. Plaques larger than 6 mm in diameter developed with some phage-host combinations, and turbid plaques, indicative of lysogeny, were also easily demonstrated for some systems.     

The bacteriophages of lactic acid bacteria with emphasis on genetic aspects of group N lactic streptococci

The paper reviews the bacteriophages of the group N lactic streptococci centering on isolation, ultrastructure and morphology, phage receptors, the structure of the genome, protein components, the phenomenon of the lysogenic state, restriction-modification systems and genetic exchange by transfection and transduction. The resulting consequences on industrial fermentations are briefly discussed.     

Comparative study of moderate and virulent phages of mesophilous lactic acid streptococci]

A method has been developed to identify phage containing mesophilous lactic acid streptococci. The method is based on the chloroform treatment of young cultures. The isolated moderate phages P4St and P6St are morphologically identical and serologically related to one another and to virulent phages P1Sv, P2Sv, P3Sv, P12Sv, P13Sv that can be isolated in industrial phagolysis.     

Agar medium for differential enumeration of lactic streptococci

An agar medium containing arginine and calcium citrate as specific substrates, diffusible (K₂HPO₄) and undiffusible (CaCO₃) buffer systems, and bromocresol purple as the pH indicator was developed to differentiate among lactic streptococci in pure and mixed cultures. Milk was added as the sole source of carbohydrate (lactose) and to provide growth-stimulating factors. Production of acid from lactose caused developing bacterial colonies to seem yellow. Subsequent arginine utilization by Streptococcus lactis and S. diacetilactis liberated ammonia, resulting in a localized pH shift back toward neutrality and a return of the original purple indicator hue. The effects of production of acid from lactose and ammonia were fixed around individual colonies by the buffering capacity of CaCO₃. After 36 hr at 32 C in a candle oats jar, colonies of S. cremoris were yellow, whereas colonies of S. lactis and S. diacetilactis were white. S. diacetilactis, on further incubation, utilized suspended calcium citrate, and, after 6 days, the citrate-degrading colonies exhibited clear zoning against a turbid background, making them easily distinguishable from the colonies of the other two species. The medium proved suitable for quantitative differential enumeration when compared with another widely used general agar medium for lactic streptococci.