Growth of Streptococcus cremoris and Streptococcus lactis in a chemostat. Production of cells and survival of bacteria during frozen storage

1973 ◽  
Vol 19 (10) ◽  
pp. 1285-1295 ◽  
Author(s):  
I. J. McDonald ◽  
B. Reiter ◽  
P. L. Rogers
Keyword(s):  
Yeast Extract ◽  
Frozen Storage ◽  
Skim Milk ◽  
Streptococcus Lactis ◽  
Streptococcus Cremoris ◽  
Constant Ph ◽  
Limiting Nutrient

Streptococcus cremoris HP and Streptococcus lactis 829 were grown in chemostats in tryptone yeast extract broth and in supplemented 2% skim milk medium. In both media, lactose was the limiting nutrient. Cultures were grown at various dilution rates in media poised at constant pH and temperature and also at constant dilution rates in media controlled at different pH levels and temperatures. The effects of the various conditions of growth on production of bacteria, viable counts, and acid-producing activities of cells and on the ability of bacteria to survive subsequent frozen storage were determined. None of the conditions of growth tested had very pronounced effects on the ability of cells to survive or on the inability of cells to retain acid-producing activity after being frozen at −70 °C and stored at −40 °C.

Growth studies on the lactic streptococci: IV. Some observations on redox potential

1972 ◽  
Vol 39 (1) ◽  
pp. 161-165 ◽  
Author(s):  
A. R. Keen
Keyword(s):  
Lactic Acid ◽  
Redox Potential ◽  
Proteolytic Activity ◽  
Skim Milk ◽  
Continuous Cultures ◽  
Batch Cultures ◽  
Reduction Cell ◽  
Streptococcus Lactis ◽  
Streptococcus Cremoris ◽  
Constant Ph

SummaryRedox potential changes at 30°C in anaerobic reconstituted skim-milk cultures ofStreptococcus cremorisAM1and AM2andStreptococcus lactisML8have been investigated in batch cultures and continuous cultures maintained at constant pH by the addition of fresh medium.Str. lactisML8was more strongly reducing than eitherStr. cremorisAM1or AM2. The positiveEhvalues which can arise in dense continuous cultures of lactic streptococci are not likely to affect either the lactic acid formation or proteolytic activity of the resultant bacterial concentrate. An electrolytic reduction cell is described which allows variations in redox potential in cultures to be controlled simply and effectively.

Behavior of Listeria monocytogenes in Skim Milk during Fermentation with Mesophilic Lactic Starter Cultures

1988 ◽  
Vol 51 (8) ◽  
pp. 600-606 ◽  
Author(s):  
MICHELLE M. SCHAACK ◽  
ELMER H. MARTH
Keyword(s):  
Lactic Acid ◽  
Listeria Monocytogenes ◽  
Lactic Acid Bacteria ◽  
Skim Milk ◽  
Starter Cultures ◽  
Plate Count ◽  
Inoculum Level ◽  
Plate Count Agar ◽  
Streptococcus Lactis ◽  
Streptococcus Cremoris

The ability of Listeria monocytogenes to grow and compete with mesophilic lactic acid bacteria was examined. Autoclaved skim milk was inoculated with 103 cells of L. monocytogenes (strain V7 or Ohio)/ml, and with 5.0, 1.0, 0.5 or 0.1% of a milk culture of either Streptococcus cremoris or Streptococcus lactis. Inoculated milks were fermented for 15 h at 21 or 30°C, followed by refrigeration at 4°C. Samples were plated on McBride Listeria Agar to enumerate L. monocytogenes and on either APT Agar or plate count agar to enumerate lactic acid bacteria. L. monocytogenes survived in all fermentations, and commonly also grew to some extent. Incubation at 30°C with 5% S. lactis as inoculum appeared to be the most inhibitory combination for strain V7, causing 100% inhibition in growth based on maximum population attained. S. cremoris at the 5.0% and 0.1% inoculum levels, was slightly less inhibitory to L. monocytogenes at 37°C, but it was slightly more inhibitory to L. monocytogenes at the 1.0% inoculum level than was S. lactis. In general, S. lactis reduced the pH of fermented milks more than did S. cremoris. The population of L. monocytogenes began to decrease before 15 h in only one test combination, which was use of a 5.0% inoculum of S. cremoris and 30°C incubation. In most instances, growth of the pathogen appeared to be completely inhibited when the pH dropped below 4.75.

Low-Temperature Activity of Lactic Streptococci Isolated from Cultured Buttermilk

1982 ◽  
Vol 45 (13) ◽  
pp. 1208-1211 ◽  
Author(s):  
STEVEN L. HOGARTY ◽  
JOSEPH F. FRANK
Keyword(s):  
Low Temperature ◽  
Skim Milk ◽  
Potential Effect ◽  
Starter Cultures ◽  
Streptococcus Lactis ◽  
Streptococcus Cremoris ◽  
Generation Times ◽  
Significant Difference ◽  
Selection Of

Psychrotrophic and mesophilic lactic streptococci were isolated from commercial cultured buttermilk to determine their potential effect on the quality of this product. These isolates consisted primarily of Streptococcus lactis subsp. diacetylactis, with S. lactis, Streptococcus cremoris, and Leuconostoc spp. also being present. Psychrotrophic isolates of S. lactis subsp. diacetylactis were compared to mesophilic isolates in regard to their ability to grow and reduce diacetyl in acidified milk (pH 4.7) incubated at 7°C. There was no significant difference detected in the ability of the two groups to reduce diacetyl (P<.05). The mesophilic isolates grew more rapidly in acidified refrigerated milk than did the psychrotrophs, indicating that the psychrotrophic isolates were more acid sensitive. The psychrotrophic isolates exhibited generation times of 9 to 11 h when grown in skim milk (pH 6.7) at 7°C. Both psychrotrophic and mesophilic strains of S. lactis subsp. diacetylactis could rapidly reduce diacetyl in refrigerated acidified milk. The results of this study suggest that procedures for selection of starter cultures for buttermilk manufacture should be improved.

Occurrence of lactose-negative mutants in chemostat cultures of lactic streptococci

1975 ◽  
Vol 21 (3) ◽  
pp. 245-251 ◽  
Author(s):  
I. J. McDonald
Keyword(s):  
Yeast Extract ◽  
Skim Milk ◽  
Starter Cultures ◽  
The Other ◽  
Batch Cultures ◽  
Streptococcus Lactis ◽  
Chemostat Cultures ◽  
Glucose Agar ◽  
Casamino Acids ◽  
Selection Of

Batch and chemostat cultures of Streptococcus cremoris HP and Streptococcus lactis 829 were examined for lactose-negative (lac−) mutants on indicator agar. In batch cultures, S. cremoris HP gave less than 1% of the total count as lac− colonies while S. lactis 829 consistently contained about 15% of the total as lac− colonies. In chemostat cultures of S. cremoris HP in 2% skim milk containing casamino acids and yeast extract (0.1% each), the percentage of lac− colonies increased markedly when the temperature of growth was 18 °C but not when the temperature of growth was 25 °C. The percentage of lac− colonies in chemostat cultures in the skim milk medium at 25 °C was about the same as that in batch cultures. On the other hand, when chemostat cultures of S. lactis 829 in the skim milk medium were grown at several temperatures between 18 and 33 °C, the percentage of lac− colonies was markedly lower than that found in batch cultures of this organism. Cultivation of S. cremoris HP in chemostats with yeast extract – lactose broth at low temperatures (14–18 °C resulted in cultures that gave plate counts on lactose agar, which were as much as 50% lower than counts on glucose agar but did not result in the selection of lac− mutants. Cultivation of S. lactis 829 in chemostats with yeast extract – glucose broth at low temperature (18 °C resulted in a selection of cells giving lac− colonies and atypical (small) lac+ colonies. The results show that cultivation of S. cremoris HP and S. lactis 829 in chemostats sometimes gave rise to altered populations. Conditions causing a change in one organism did not necessarily cause a similar change in the other. The results indicate that the successful propagation of lactic streptococci in chemostats for use as starter cultures in the dairy industry will require the careful establishment of optimum conditions for every strain so as to minimize the possible selection of undesirable populations.

Preparation of a highly active form of nisin from Streptococcus lactis

1971 ◽  
Vol 17 (1) ◽  
pp. 61-67 ◽  
Author(s):  
F. J. Bailey ◽  
A. Hurst
Keyword(s):  
Active Form ◽  
Gradient Elution ◽  
Antibiotic Activity ◽  
Complex Medium ◽  
Main Peak ◽  
Acetone Precipitation ◽  
Highly Active ◽  
Streptococcus Lactis ◽  
Constant Ph ◽  
Ph Gradient Elution

Cells of Streptococcus lactis (354/07) synthesized and retained nisin when grown in a complex medium with 2.5% glucose at a constant pH of 6.7. Nisin was extracted from cells by a previously used method with hot 0.05 N HCl but milder methods of extraction from whole and broken cells using a variety of solvents were also tested. In the preferred method broken cells were extracted with 0.05 N HCl at 2 °C. The Cl− ions of the extract were exchanged for acetate on columns of the resin Amberlite CG 4B and the eluate was concentrated by acetone precipitation at −19 °C. The nisin was finally purified by pH gradient elution from CM cellulose columns. Three peaks with antibiotic activity were found, two of the peaks were minor and represented less than 5% of the nisin. The main peak gave a single band on electrophoresis. Electrophoresis of the material from the CM cellulose peaks revealed about 44 bands of basic proteins. Nisin made by the hot or cold HCl extraction behaved similarly in electrophoresis and CM cellulose chromatography but the antibiotic activity of the material isolated from the cold extract was nine times greater than that of the material isolated from the hot extract.

NUTRITIONAL EVALUATION OF AN ENSILED PRODUCT FROM FISH

1965 ◽  
Vol 43 (11) ◽  
pp. 1879-1883 ◽  
Author(s):  
M. A. Krishnaswamy ◽  
S. B. Kadkol ◽  
G. D. Revankar
Keyword(s):  
Protein Efficiency Ratio ◽  
Milk Powder ◽  
Skim Milk ◽  
Skim Milk Powder ◽  
Efficiency Ratio ◽  
Protein Ratio ◽  
Protein Utilization ◽  
Streptococcus Lactis ◽  
Available Lysine ◽  
Net Protein

Ensiled fish was prepared from a local variety of freshwater fish (Barbus carnaticus) by fermentation with a pure culture of Streptococcus lactis, commercial lactose being used as a source of fermentable carbohydrate. The fermented material (pH 4.7) was roller dried. The finished product was cream colored and had a somewhat aromatic odor. It had a protein content of about 72%. Total lysine, available lysine, methionine, cystine, and tryptophan of the ensiled fish (expressed as g/16 g N) were 10.1, 8.1, 3.6, 1.1, and 1.2%, respectively. Hygienically, the product, being free from coliforms, enterococci, Salmonella, coagulase-positive staphylococci, and pathogenic anaerobes, was satisfactory. The biological value of the product as determined by protein efficiency ratio (3.3), net protein utilization (82.3%), and net protein ratio (4.2) was not significantly different from that of skim milk powder, which has a protein efficiency ratio of 3.2, net protein utilization of 82.8%, and net protein ratio of 4.9.

Acid Production and Proteolytic Activity in Milk by Gamma-Irradiation Induced Mutants of Lactobacilli

1977 ◽  
Vol 40 (9) ◽  
pp. 600-602 ◽  
Author(s):  
JASJIT SINGH ◽  
B. RANGANATHAN
Keyword(s):  
Gamma Irradiation ◽  
Proteolytic Activity ◽  
Acid Production ◽  
Lactobacillus Casei ◽  
Amino Nitrogen ◽  
Lactobacillus Bulgaricus ◽  
Soluble Nitrogen ◽  
Streptococcus Lactis ◽  
Streptococcus Cremoris ◽  
Induced Mutants

Biochemical changes in selected gamma-irradiation induced mutants of Lactobacillus bulgaricus and Lactobacillus casei were examined. Cultures were tested after 24 h of incubation at 37 C for titratable and volatile acidities and proteolytic activity. The gamma-irradiation induced mutants exhibited 50–95% greater proteolytic activity than the unirradiated parent culutres. Some of the mutants produced greater titratable and volatile acidities in milk as compared to parent cultures. Two mutant cultures, Lb/G-1 from L. bulgaricus 59 and Lc/G-1 from L. casei RTS released significantly greater amounts of soluble nitrogen and amino nitrogen in whole casein and selected fractions than did parent cultures. Combining the mutant cultures with Streptococcus lactis C10 or Streptococcus cremoris C1 resulted in greater acid producing ability than that of the parent cultures mixed with the streptococci.

scholarly journals Complex regulation of AprA metalloprotease in Pseudomonas fluorescens M114: evidence for the involvement of iron, the ECF sigma factor, PbrA and pseudobactin M114 siderophore

Microbiology ◽  
2006 ◽  
Vol 152 (1) ◽  
pp. 29-42 ◽  
Author(s):  
Bláithín Maunsell ◽  
Claire Adams ◽  
Fergal O'Gara
Keyword(s):  
Pseudomonas Fluorescens ◽  
Proteolytic Activity ◽  
Yeast Extract ◽  
Sigma Factor ◽  
Skim Milk ◽  
Protease Production ◽  
Iron Starvation ◽  
Transcription Analysis ◽  
Skim Milk Agar ◽  
Complex Regulation

In the soil bacterium Pseudomonas fluorescens M114, extracellular proteolytic activity and fluorescent siderophore (pseudobactin M114) production were previously shown to be co-ordinately negatively regulated in response to environmental iron levels. An iron-starvation extracytoplasmic function sigma factor, PbrA, required for the transcription of siderophore biosynthetic genes, was also implicated in M114 protease regulation. The current study centred on the characterization and genetic regulation of the gene(s) responsible for protease production in M114. A serralysin-type metalloprotease gene, aprA, was identified and found to encode the major, if not only, extracellular protease produced by this strain. The expression of aprA and its protein product were found to be subject to complex regulation. Transcription analysis confirmed that PbrA was required for full aprA transcription under low iron conditions, while the ferric uptake regulator, Fur, was implicated in aprA repression under high iron conditions. Interestingly, the iron regulation of AprA was dependent on culture conditions, with PbrA-independent AprA-mediated proteolytic activity observed on skim milk agar supplemented with yeast extract, when supplied with iron or purified pseudobactin M114. These effects were not observed on skim milk agar without yeast extract. PbrA-independent aprA expression was also observed from a truncated transcriptional fusion when grown in sucrose asparagine tryptone broth supplied with iron or purified pseudobactin M114. Thus, experimental evidence suggested that iron mediated its effects via transcriptional activation by PbrA under low iron conditions, while an as-yet-unidentified sigma factor(s) may be required for the PbrA-independent aprA expression and AprA proteolytic activity induced by siderophore and iron.

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