Influence of wine-like conditions on arginine utilization by lactic acid bacteria

Wine can contain trace amounts of ethyl carbamate (EC), a carcinogen formed when ethanol reacts with carbamyl compounds such as citrulline. EC is produced from arginine by lactic acid bacteria (LAB), e.g., Lactobacillus and Pediococcus. Although the amounts of EC in wine are usually negligible, over the last few years there has been a slight but steady increase, as climate change has increased temperatures and alcohol levels have become proportionately higher, both of which favor EC formation. In this study, resting cells of LAB were used to evaluate the effects of ethanol, glucose, malic acid, and low pH on the ability of non-oenococcal strains of these bacteria to degrade arginine and excrete citrulline. Malic acid was found to clearly inhibit arginine consumption in all strains. The relation between citrulline produced and arginine consumed was clearly higher in the presence of ethanol (10-12%) and at low pH (3.0), which is consistent with both the decreased amount of ornithine produced from arginine and the reduction in arginine degradation. In L. brevis and L. buchneri strains isolated from wine and beer, respectively, the synthesis of citrulline from arginine was highest.     

Genetics of lactose utilization in lactic acid bacteria

Abstract: Lactose utilization is the primary function of lactic acid bacteria used in industrial dairy fermentations. The mechanism by which lactose is transported determines largely the pathway for the hydrolysis of the internalized disaccharide and the fate of the glucose and galactose moieties. Biochemical and genetic studies have indicated that lactose can be transported via phosphotransferase systems, transport systems dependent on ATP binding cassette proteins, or secondary transport systems including proton symport and lactose-galactose antiport systems. The genetic determinants for the group translocation and secondary transport systems have been identified in lactic acid bacteria and are reviewed here. In many cases the lactose genes are organized into operons or operon-like structures with a modular organization, in which the genes encoding lactose transport are tightly linked to those for lactose hydrolysis. In addition, in some cases the genes involved in the galactose metabolism are linked to or co-transcribed with the lactose genes, suggesting a common evolutionary pathway. The lactose genes show characteristic configurations and very high sequence identity in some phylogenetically distant lactic acid bacteria such as Leuconostoc and Lactobacillus or Lactococcus and Lactobacillus . The significance of these results for the adaptation of lactic acid bacteria to the industrial milk environment in which lactose is the sole energy source is discussed.     

D-amino acids in the cell pool of bacteria

About 30 different bacterial species were tested for the possible presence of freed-amino acids in their cell pool. Gram-positive bacteria particularly the species of the genusBacillus have a fairly large pool of freely extractabled-amino acids. Varied quantities of freed-amino acids were detected inBacillus subtilis B₃,Bacillus subtilis Marburg,Bacillus licheniformis, Bacillus brevis, Bacillus stearothermophilus, Lactobacillus fermenti, Lactobacillus delbrueckii, Staphylococcus aureus andClostridium acetobutylicum. The individual components ofd-amino acids were identified in 5Bacillus species referred to above,d-alanine is the major component; the otherd-amino acids identified are aspartic acid, glutamic acid, histidine, leucines, proline, serine and tyrosine. Thed-amino acid pool size inBacillus subtilis B₃ varies with different culture conditions. The pool size is maximum when growth temperature is 30°C and it fluctuates with change in pH of the medium. The maximum quantity ofd-amino acids could be recovered when the culture was at mid log phase. O₂ supply to the medium has little effect ond-amino acid pool size. The starvation of cells leads to depletion of thed-amino acid pool which is exhausted almost completely within 4 hours by incubation in nutrient-free medium.     

Influence of carbohydrates on the isolation of lactic acid bacteria

Aims: To determine the influence of carbohydrates on enrichment isolation of lactic acid bacteria from different niches. Methods and Results: Lactic acid bacteria in three traditional fermented products in southern Africa (amasi, mahewu and tshwala) and in three fresh samples (two flowers and a fruit) were enrichment cultured in media supplemented with 13 different carbohydrates. Diversity of lactic acid bacteria was determined by PCR‐denaturing‐gradient gel electrophoresis. Carbohydrates used in enrichment media had a big impact on the isolation of lactic acid bacteria from fermented products. Depending on the carbohydrates tested, the number of species detected ranged from one to four in amasi, one to five in mahewu and one to three in tshwala. Fructose and mannitol selected for relatively higher numbers of lactic acid bacteria in fermented products. Specific relationships between substrates and lactic acid bacteria have been noted. On the other hand, small influences were found among carbohydrates tested in flowers and fruit. Conclusion: Carbohydrates have a big impact on the isolation of a variety of lactic acid bacteria in fermented food. Significance and Impact of the Study: This is the first study that reports the influence of carbohydrates on the enrichment of lactic acid bacteria.     

Response of lactic acid bacteria to amino acid derivatives. II. Glycine

The response of five lactobacilli (for which glycine is an essential nutrient) to two tripeptides, five dipeptides, and seventeen other glycine derivatives has been tested over a range of concentrations and at four or five incubation times from 18 to 229 hours. In general the activities decreased with increasing concentrations and incubation times although in some cases they remained nearly constant, increased, or increased and then decreased. Hippuric acid, all of the dipeptides, and the tripeptide, l-leucylglycylglycine, exhibited greater activity than glycine for one or more of the organisms. These results may be interpreted to signify that (a) the apparent decrease in apparent glycine in hydrolyzed urines may be accounted for in part by the higher activity of hippuric acid in unhydrolyzed urines, and (b) some peptides may be utilized directly by lactic acid bacteria under some conditions.