Influence of pH,lactose and lactic acid on the growth of Streptococcus cremoris: a kinetic study

Summary The effect of various culture conditions on growth kinetics of an homofermentative strain of the lactic acid bacterium Streptococcus cremoris were investigated in batch cultures, in order to facilitate the production of this organism as a starter culture for the dairy industry. An optimal pH range of 6.3–6.9 was found and a lactose concentration of 37 g·l^-1 was shown to be sufficient to cover the energetic demand for biomass formation, using the recommended medium. The study of the effect of lactic acid concentration on growth kinetics revealed that the end-product was not the sole factor affecting growth. The strain was characterized for its tolerance towards lactic acid and a critical concentration of 70 g·l^-1 demonstrated. With the product yield of 0.9 g·g^-1 at non-lactose limiting conditions the lactic acid concentration of 33 g·l^-1 could not explain the low growth rates obtained, implicating a nutritional limitation.Symbols t _f fermentation duration (h) - X Biomass concentration (g·l^-1) - X _m maximum biomass concentration (g·l^-1) - S lactose concentration (g·l^-1) - S _r residual lactose concentration (g·l^-1) - P produced lactic acid concentration (g·l^-1) - P _a added lactic acid concentration (g·l^-1) - P _c critical lactic acid concentration (g·l^-1) - specific growth rate (h^-1) - _max maximum specific growth rate (h^-1) - R _x/S biomass yield (g·g^-1) calculated when =0 - R _P/S product yield (g·g^-1)     

Influence of pH and lactic acid concentration on Clostridium tyrobutyricum during continuous growth in a pH-auxostat

The aim of this project was to establish the minimal inhibitory concentration (MIC) of lactic acid for growth of Clostridium tyrobutyricum. A pH-auxostat was used to maintain a constant pH and to allow continuous growth at the highest possible rates at fixed, but adjustable concentrations of lactate. By raising the concentration of lactic acid and keeping the pH constant, the growth rate was shown to decrease linearly with increasing lactic acid concentration. The p K _a of lactic acid, measured in the actual growth medium at 37°C, was 3.40 (±0.03). Based on this value, the MIC_undiss values for each pH were estimated. The MIC of total lactic acid (MIC_tot) ranged from 150 mmol l⁻¹ to 1510 mmol l⁻¹ at pH 4.6–6.25, respectively. The corresponding MIC values of undissociated lactic acid (MIC_undiss) ranged from 8.9 to 2.1 mmol l⁻¹ at the same pH values. These results emphasize the importance of a rapid pH decrease and an equally rapid initial lactic acid fermentation of the ensilage, in order to sufficiently suppress clostridial growth.     

Plasmid-directed mechanisms for bacteriophage defense in lactic streptococci

Abstract Genetic studies with lactic streptococci have identified a variety of plasmids coding for systems that interfere with phage adsorption, direct restriction and modification activities, and disrupt various stages in the phage lytic cycle. This review describes mechanisms of phage defense that are plasmid-directed in lactic streptococci, examines the physical and genetic properties of the plasmids involved, and discusses genetic strategies for construction of phage-insensitive starter cultures for dairy fermentations.     

Bacteriophage and bacteriophage resistance in lactic acid bacteria

Abstract: The study of bacteriophage-host interactions has been instrumental in the development of genetic systems in many genera, and laid many of the foundations of modern molecular genetics. Research into bacteriophage and bacteriophage resistance in the lactic acid bacteria has moved into a new and exciting dimension in recent years. Mechanisms such as adsorption inhibition, restriction and modification, and abortive infection which have been detected and described phenotypically over the past decade are now being subjected to molecular analysis, and this has led to a better understanding of the nature and variety of resistance systems employed by lactic acid bacteria to combat phage attack. In addition, analysis of different bacteriophage has increased our knowledge of these ubiquitous particles to the point where it is possible to construct novel phage resistances based on the phage genome itself. This review outlines the recent progress in the molecular analysis of bacteriophage, bacteriophage resistance and counter resistance, and the construction of novel resistance mechanisms.     

Choline-containing bacteriophage receptors in Streptococcus pneumoniae.

Choline-containing teichoic acid seems to be essential for the adsorption of bacteriophage Dp-1 to pneumococci. This conclusion is based on the following observations: In contrast to pneumococci grown in choline-containing medium, cells grown in medium containing ethanolamine or other submethylated aminoalcohols instead of choline were found to be resistant to infection by Dp-1. Live choline-grown bacteria and heat- or UV-inactivated cells and purified cell walls prepared from these cells were capable of adsorbing phage Dp-1; ethanolamine-grown pneumococci or cell wall preparations were unable to do so. Adsorption of Dp-1 to choline-containing cell walls was competitively inhibited by phosphorylcholine and by several choline-containing soluble cell surface components, such as the Forssman antigen and the teichoic acid-glycan complexes formed by autolytic cell wall degradation. Cell walls prepared from pneumococci grown in ethanolamine or phosphorylethanolamine were inactive. Electron microscopic studies with pneumococci that had segments of choline-containing cell wall material amid ethanolamine-containing regions indicated that the Dp-1 phage particles adsorbed exclusively to the choline-containing surface areas. We suggest that the choline residues of the pneumococcal teichoic acid are essential components of the Dp-1 phage receptors in this bacterium.     

Transfection of Streptococcus pneumoniae with bacteriophage DNA.

It was possible to transfect Streptococcus pneumoniae with DNA obtained from a newly isolated bacteriophage, diplophage-4 (Dp-4). Optimal frequency of transfection (0.9%) required the use of a nuclease-defective mutant; with wild-type bacteria, the transfection frequency was about 100-fold lower. Transfection requires physiological conditions that appear to be similar to the competent state needed for genetic transformation (A. Tomasz, J. Bacteriol. 91:1050--1061, 1966).     

Genome sequence of Streptococcus mutans bacteriophage M102

Bacteriophage M102 is a lytic phage specific for serotype c strains of Streptococcus mutans, a causative agent of dental caries. In this study, the complete genome sequence of M102 was determined. The genome is 31,147 bp in size and contains 41 ORFs. Most of the ORFs encoding putative phage structural proteins show similarity to those from bacteriophages from Streptococcus thermophilus. Bioinformatic analysis indicated that the M102 genome contains an unusual lysis cassette, which encodes a holin and two lytic enzymes.     

Purification of Streptococcus group C bacteriophage lysin.

A simple procedure for the purification of Streptococcus group C phage lysin to apparent homogeneity is described. The electrophoretically pure, enzymatically stable polypeptide of 98,000 molecular weight converted Streptococcus (groups A, F, and H) cells into spheroplasts within 5 min at 0 degrees C or within less than a minute at 37 degrees C.     

Influence of lactic acid on the proliferation,metabolism, and differentiation of rabbit mesenchymal stem cells

Lactic acid, originated from degradation of biomaterials, cell cultures, and so on, would be a toxic compound in acute states. The present study was undertaken to ascertain whether the proliferation, metabolism, and differentiation of rabbit mesenchymal stem cells (rMSCs) were affected by additional lactic acid. Furthermore, this study aimed to determine whether this influence was due to decreasing pH, increasing osmotic pressure, or chemical action of lactate ion. It was shown that the proliferation and metabolism of MSCs were inhibited by decreasing pH or increasing lactate. However, when osmolarity was adjusted to the same level as that of sodium lactate using sodium chloride, cell proliferation was little affected by osmotic pressure. We also concluded that colony-forming potential and osteogenic differentiation capacity were significantly depressed by decreasing pH or increasing lactate. As was shown, this inhibition of lactate was not only due to osmotic pressure, but also mainly due to chemical action of lactate ion. However, we observed that acidifying extracellular medium and lactate ion promoted the retention of adipogenic differentiation potential of MSCs during in vitro expansion, which suggested that growth arrest and the decrease of osteogenic differentiation potential did not affect the adipogenic conversion of MSCs.     

Growth Phase and pH Influence Peptide Signaling for Competence Development in Streptococcus mutans

The development of competence by the dental caries pathogen Streptococcus mutans is mediated primarily through the alternative sigma factor ComX (SigX), which is under the control of multiple regulatory systems and activates the expression of genes involved in DNA uptake and recombination. Here we report that the induction of competence and competence gene expression by XIP (sigX-inducing peptide) and CSP (competence-stimulating peptide) is dependent on the growth phase and that environmental pH has a potent effect on the responses to XIP. A dramatic decline in comX and comS expression was observed in mid- and late-exponential-phase cells. XIP-mediated competence development and responses to XIP were optimal around a neutral pH, although mid-exponential-phase cells remained refractory to XIP treatment, and acidified late-exponential-phase cultures were resistant to killing by high concentrations of XIP. Changes in the expression of the genes for the oligopeptide permease (opp), which appears to be responsible for the internalization of XIP, could not entirely account for the behaviors observed. Interestingly, comS and comX expression was highly induced in response to endogenously overproduced XIP or ComS in mid-exponential-phase cells. In contrast to the effects of pH on XIP, competence induction and responses to CSP in complex medium were not affected by pH, although a decreased response to CSP in cells that had exited early-exponential phase was observed. Collectively, these results indicate that competence development may be highly sensitive to microenvironments within oral biofilms and that XIP and CSP signaling in biofilms could be spatially and temporally heterogeneous.