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.

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.

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.

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.

Note on Selection of Coordinate Systems for Geodynamics

1975 ◽  
Vol 26 ◽  
pp. 395-407
Author(s):  
S. Henriksen
Keyword(s):  
Sea Level ◽  
The Other ◽  
Coordinate Systems ◽  
Mean Sea Level ◽  
The Earth ◽  
The One ◽  
Static Systems ◽  
Selection Of

The first question to be answered, in seeking coordinate systems for geodynamics, is: what is geodynamics? The answer is, of course, that geodynamics is that part of geophysics which is concerned with movements of the Earth, as opposed to geostatics which is the physics of the stationary Earth. But as far as we know, there is no stationary Earth – epur sic monere. So geodynamics is actually coextensive with geophysics, and coordinate systems suitable for the one should be suitable for the other. At the present time, there are not many coordinate systems, if any, that can be identified with a static Earth. Certainly the only coordinate of aeronomic (atmospheric) interest is the height, and this is usually either as geodynamic height or as pressure. In oceanology, the most important coordinate is depth, and this, like heights in the atmosphere, is expressed as metric depth from mean sea level, as geodynamic depth, or as pressure. Only for the earth do we find “static” systems in use, ana even here there is real question as to whether the systems are dynamic or static. So it would seem that our answer to the question, of what kind, of coordinate systems are we seeking, must be that we are looking for the same systems as are used in geophysics, and these systems are dynamic in nature already – that is, their definition involvestime.

INTERFERENSI GRAMATIKAL DALAM KUMPULAN CERPEN BIARKAN AKU MEMULAI KARYA NURUL F. HUDA

2019 ◽  
Vol 1 (01) ◽  
pp. 16-23
Author(s):  
Zimmatul Liviana
Keyword(s):  
Short Stories ◽  
Data Collection ◽  
Qualitative Method ◽  
Language Variation ◽  
The Other ◽  
Qualitative Descriptive ◽  
Ofthe Object ◽  
Selection Of ◽  
Descriptive Qualitative

The research grammatical interference in a collection ofshort stories Biarkan Aku Memula iwork Nurul F. Hudaisa collection ofshort storiesset in the back that Is start work Let Nurul F. Huda contains many grammatical interference.The problem of this   study were(1)how   the various morphologi calinterference containedin   a   collection of short stories Biarkan Aku Memulai work Nurul F. Huda. (2)how the various syntactic interference contained in a collection of short stories Biarkan Aku Memulai work Nurul F. Huda. The purposeof this studyis to describe the morphological and         Syntactic interference contained in a collection of short stories Biarkan Aku Memulai work Nurul F. Huda. Sociolinguistics is the study of language variation and use in society. Interference is the event of the use of language elements of one into the other language elements that occur in the speakers themselves. This research uses descriptive qualitative method because to describe the actual realityin order to obtainan accurateand objective. Qualitative descriptive methods were used to analyzethe elements ofa word orphrase that incorporated elements of other languages with the analysis and description of the formulation of the problem is the answer. Data collection techniques using observation techniques, the determination ofthe object of research, the selection of short stories.Based on the analysis of the data in this study can be found that there are six forms of interference morphology, namely (1) the prefix nasal N-sound, (2) the addition of the suffix, (3) the exchange prefix, (4) exchange suffixes, (5) exchange konfiks, (6) removal affixes. While the syntactic interference only on the words and phrases in a sentence. The results of the study it can be concluded that the interference morphology more common than syntactic interference.

The role of a metabolic intermediate in the biodegradation of inhibitory substrates

1997 ◽  
Vol 36 (10) ◽  
pp. 27-36 ◽  
Author(s):  
P. Mungkarndee ◽  
S. M. Rao Bhamidimarri ◽  
A. J. Mawson ◽  
R. Chong
Keyword(s):  
The Other ◽  
Metabolic Product ◽  
Dichlorophenoxyacetic Acid ◽  
Mutual Inhibition ◽  
Metabolic Intermediate ◽  
Batch Cultures ◽  
Ortho Cresol ◽  
2,4 Dichlorophenoxyacetic Acid

Biodegradation of the mixed inhibitory substrates, 2,4-dichlorophenoxyacetic acid (2,4-D) and para-chloro-ortho-cresol (PCOC) was studied in aerobic batch cultures. Each substrate added beyond certain concentrations inhibited the degradation of the other. This mutual inhibition was found to be enhanced by 2,4-dichlorophenol (2,4-DCP) which is an intermediate metabolic product of 2,4-D. When 2,4-DCP accumulated to approximatelY 40 mg/l degradation of all compounds in the mixed 2,4-D and PCOC substrate system was completely inhibited. The degradation of 2,4-D and PCOC individually was also found to be inhibited by elevated concentrations of 2,4-DCP added externally, while PCOC inhibited the utilization of the intermediate.

The influence of the initial concentrations of glucose and yeast extract on the ethanolic fermentation by Pachysolen tannophilus

1990 ◽  
Vol 55 (3) ◽  
pp. 854-866 ◽  
Author(s):  
Rodríguez V. Bravo ◽  
Rubio F. Camacho ◽  
Villasclaras S. Sánchez ◽  
Vico M. Castro
Keyword(s):  
Cell Growth ◽  
Ethanol Production ◽  
Yeast Extract ◽  
Culture Medium ◽  
Ethanolic Fermentation ◽  
Pachysolen Tannophilus ◽  
Significant Component ◽  
Batch Cultures

The ethanolic fermentation in batch cultures of Pachysolen tannophilus was studied experimentally varying the initial concentrations of two of the components in the culture medium: glucose between 0 and 200 g l-1 and yeast extract between 0 and 8 g l-1. The yeast extract appears to be a significant component both in cell growth and for ethanol production.

The Propaganda Feedback Loop

2018 ◽  
Author(s):  
Yochai Benkler ◽  
Robert Faris ◽  
Hal Roberts
Keyword(s):  
Case Studies ◽  
Feedback Loop ◽  
The Other ◽  
Hillary Clinton ◽  
Donald Trump ◽  
The Public ◽  
False Reporting ◽  
Media Ecosystem ◽  
Crowd Out ◽  
Selection Of

This chapter presents a model of the interaction of media outlets, politicians, and the public with an emphasis on the tension between truth-seeking and narratives that confirm partisan identities. This model is used to describe the emergence and mechanics of an insular media ecosystem and how two fundamentally different media ecosystems can coexist. In one, false narratives that reinforce partisan identity not only flourish, but crowd-out true narratives even when these are presented by leading insiders. In the other, false narratives are tested, confronted, and contained by diverse outlets and actors operating in a truth-oriented norms dynamic. Two case studies are analyzed: the first focuses on false reporting on a selection of television networks; the second looks at parallel but politically divergent false rumors—an allegation that Donald Trump raped a 13-yearold and allegations tying Hillary Clinton to pedophilia—and tracks the amplification and resistance these stories faced.

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