Transient self-inhibition of the growth of Lactobacillus delbrueckii subsp. bulgaricus in a pH-regulated fermentor

An industrial strain of Lactobacillus delbrueckii subsp. bulgaricus was grown in a synthetic medium on lactose as carbon substrate, in a pH-regulated fermentor. Growth proceeded in two distinct phases separated by a transient stationary phase. Various experimental approaches were used to identify the cause of this growth arrest. Growth experiments in L. bulgaricus culture supernatant fluids collected at different cultivation times in fermentor, and supplemented or not with various nutritional solutions, enabled us to discard the possibility of a nutritional limitation. Tube cultures of L. bulgaricus in medium supplemented with various lactic acid concentrations showed a potential inhibition by this metabolic end product but confirmed that this inhibition was not responsible for the cessation of growth. It was concluded that at least one inhibitory compound was produced during the growth phase of the strain, and this compound disappeared from the medium in the transient stationary phase, enabling the growth to start again later in the culture. Indeed, the stoichiometric analysis of the culture showed, firstly, that unidentified carbon compounds were produced from lactose during growth, which were probably converted in lactic acid during the transient stationary phase and, secondly, that part of the amino acids consumed gave catabolic end products. Finally, bacteriocin-like compounds were not considered to be responsible for this growth arrest.     

Study on lyotropic liquid-crystalline properties of trimethylsilyl hydroxypropylcellulose

The lyotropic liquid-crystalline behavior of trimethylsilyl hydroxypropylcellulose (TMS-HPC) is reported in this paper. The introduction of the trimethylsilyl (TMS) group in the parent HPC increases the solubility in organic solvents, and the lyotropic mesophase can be formed in concentrated acetone solution. The critical concentration (C*) in acetone is approximately 36%. The liquid crystalline nature of TMS-HPC/acetone solution was confirmed by PLM, and the mechanism of liquid crystallization was studied by FTIR and WAXD methods.     

High yield regioselective monobenzyloxycarbonylation of secondary alcohols in glycopyranoside series

The regioselective monobenzyloxycarbonylation of secondary alcohols in methyl 6-O-(4-methoxytrityl)-alpha-D-manno-, gluco- and galactopyranoside has been achieved in high yields (74-85%) by using benzyl chloroformate in the presence of 4-dimethylaminopyridine and/or 1,4-diazabicyclo[2.2.2]octane.     

Multilevel phenotypic selection on morphological characters in a metapopulation of Silene tatarica

This study partitions selection in a natural metapopulation of a riparian plant species, Silene tatarica, into individual- and patch-level components by using contextual analysis, in which a patch refers to a spatially distinct stand of individual plants. We estimated selection gradients for two morphological characters (plant height and number of stems), their respective patch means, and plant density with respect to reproductive success in a two-year study. The approach was also extended to partition selection separately within habitats with varying degrees of exposure to river disturbances and herbivory. The selection differentials and gradients for plant height were positive at both individual and patch levels, with selection forces highest in the closed habitat with low exposure to disturbance. This pattern suggests that local groups with taller than average plants are more visible to pollinators than to groups that are shorter than average plants; and, within patches, individuals with short stature are visited less often than taller ones. Selection on the number of stems was in opposition at individual and patch levels. At the individual level the character was selected toward higher values, whereas selection at the patch-level favored smaller mean number of stems. The strength of the latter component was associated with the intensity of herbivory in different habitats, suggesting that the patch-level selection against a large number of stems might be due to high attractiveness of such patches to the main herbivore, reindeer. Consequently, direction and strength of selection in spatially structured populations may depend significantly on fitness effects arising at the group level.     

Offspring food allocation by parents and helpers in a cooperative mammal

In cooperatively breeding species, helpers and parents commonlyface two decisions when they find a food item: first, whetherto feed the item to a young group member or to eat it themselves;and second, which offspring to feed. Little is known aboutthe factors that influence these decisions in cooperative mammals,though optimal foraging theory provides a basis for a rangeof predictions. In this article we describe pup feeding behaviorby helpers and parents in a cooperative mongoose, the meerkat(Suricata suricatta). When meerkat pups begin accompanyingthe group, they beg food from older group members, who digup dispersed prey items. As predicted, the probability of aprey item being fed to a pup shows a positive relationship with prey size and a negative relationship with pup distance.Meerkats apparently follow a "feed the nearest pup rule" andare more likely to feed the nearest pup if it is hungry. Hungrierpups beg more and follow older group members more closely.Across all age categories, females feed pups more frequentlythan males, both in terms of the relative frequency of feeds,and the proportion of prey biomass found by each individualthat is fed to pups. Females also feed female pups significantlymore than male pups, while males feed pups of both sexes equally.These sex biases in feeding contributions may result from femalegroup members benefiting more than males from higher pup survival,and in particular higher female pup survival, because femalesare the philopatric sex.     

A prevalence survey for zoonotic enteric bacteria in a research monkey colony with specific emphasis on the occurrence of enteric Yersinia

Transmissible pathogenic and opportunistic zoonotic enteric bacteria comprise a recognized occupational health threat to exposed humans from non-human primates (NHPs). In an effort to evaluate the occurrence of selected enteric organisms with zoonotic and biohazard potential in a research colony setting, we performed a prevalence study examining 61 juvenile and young adult rhesus macaques participating in a transplant immunology project. Primary emphasis was directed specifically to detection of pathogenic enteric Yersinia, less well-documented and reported NHP pathogens possessing recognized significant human disease potential. NHPs were surveyed by rectal culture during routine health monitoring on three separate occasions, and samples incubated using appropriate media and specific selective culture methods. Enteric organisms potentially transmissible to humans were subcultured and identified to genus and species. Significant human pathogens of the Salmonella/Shigella, Campylobacter, and enteric Yersinia groups were not isolated throughout the survey, suggesting prevalence of these organisms may generally be quite low.     

One step purification of glucose-6-phosphate dehydrogenase from brain areas by immunoaffinity chromatography

Glucose-6-phosphate dehydrogenase was purified from rabbit brain cortex using a single immunoaffinity chromatographic step and was contaminated only by a 50 kDa protein. The proteins, separated by SDS-PAGE, were sequenced: the glucose-6-phosphate dehydrogenase was blocked at the N-terminal, the co-eluted protein was similar to -tubulin. Our technique can be applied to purification and sequencing of the enzyme from brain areas or to measure its turnover rate in cultured cells.     

Control of biogenic H(2)S production with nitrite and molybdate

The effects of the metabolic inhibitors, sodium nitrite and ammonium molybdate, on production of H₂S by a pure culture of the sulfate-reducing bacterium (SRB) Desulfovibrio sp. strain Lac6 and a consortium of SRB, enriched from produced water of a Canadian oil field, were investigated. Addition of 0.1 mM nitrite or 0.024 mM molybdate at the start of growth prevented the production of H₂S by strain Lac6. With exponentially growing cultures, higher levels of inhibitors, 0.25 mM nitrite or 0.095 mM molybdate, were required to suppress the production of H₂S. Simultaneous addition of nitrite and molybdate had a synergistic effect: at time 0, 0.05 mM nitrite and 0.01 mM molybdate, whereas during the exponential phase, 0.1 mM nitrite and 0.047 mM molybdate were sufficient to stop H₂S production. With an exponentially growing consortium of SRB, enriched from produced water of the Coleville oil field, much higher levels of inhibitors, 4 mM nitrite or 0.47 mM molybdate, were needed to stop the production of H₂S. The addition of these inhibitors had no effect on the composition of the microbial community, as shown by reverse sample genome probing. The results indicate that the efficiency of inhibitors in containment of SRB depends on the composition and metabolic state of the microbial community. Journal of Industrial Microbiology & Biotechnology (2001) 26, 350–355. Received 02 August 2000/ Accepted in revised form 17 April 2001     

Rapid detection and quantification of five periodontopathic bacteria by real-time PCR

The quantity of periodontopathic bacteria in plaque samples is an important determinant for understanding the etiologic role of bacteria. The real-time PCR method was used to detect and quantify periodontopathic bacteria, such as Actinobacillus actinomycetemcomitans, Bacteroides forsythus, Porphyromonas gingivalis, Treponema denticola, and Treponema socranskii, in saliva and subgingival plaque samples. There was good agreement between the results of conventional PCR and real-time PCR methods. Using the LightCycler system we were able to determine the amount of periodontopathic bacteria within an hour. The real-time PCR method was linear for samples containing from 10(3) to more than 10(8) cells (r2 = 0.999). The application of the real-time PCR method should be useful in the rapid detection and quantification of periodontopathic bacteria in clinical samples.     

Mutualistic relationships between phytoplankton and bacteria caused by carbon excretion from phytoplankton

For the competition system of phytoplankton and bacteria through inorganic phosphorus, our mathematical model showed that mutualistic relationships between them could occur due to production and consumption of extracellular organic carbon by phytoplankton and bacteria. In our model, phytoplankton are limited in their growth by light and phosphorus, and bacteria are limited in their growth by phosphorus and carbon released from phytoplankton. We adopted permanence as a criterion of the coexistence in mathematical analysis, and led necessary conditions of permanence in the model. Under these coexistence conditions, we estimated the strength of total effects of interactions between phytoplankton and bacteria at the steady state by press perturbation method. The results of this estimation indicated the mutualistic interactions between phytoplankton and bacteria. This suggests that mutualistic situation could occur due to the introduction of carbon flow from phytoplankton to bacteria, even if phytoplankton and bacteria compete with each other through common resource, inorganic phosphorus.