Cell division in <Emphasis Type="Italic">Escherichia coli</Emphasis>cultures monitored at single cell resolution

Background  

A fundamental characteristic of cells is the ability to divide. To date, most parameters of bacterial cultures, including cell division, have been measured as cell population averages, assuming that all bacteria divide at a uniform rate.     

Specialized persister cells and the mechanism of multidrug tolerance in Escherichia coli

Bacterial populations produce persisters, cells that neither grow nor die in the presence of bactericidal agents, and thus exhibit multidrug tolerance (MDT). The mechanisms of MDT and the nature of persisters have remained elusive. Our previous research has shown that persisters are largely responsible for the recalcitrance of biofilm infections. A general method for isolating persisters was developed, based on lysis of regular cells by ampicillin. A gene expression profile of persisters contained toxin-antitoxin (TA) modules and other genes that can block important cellular functions such as translation. Bactericidal antibiotics kill cells by corrupting the target function (for example, aminoglycosides interrupt translation, producing toxic peptides). We reasoned that inhibition of translation will lead to a shutdown of cellular functions, preventing antibiotics from corrupting their targets, giving rise to MDT persister cells. Overproduction of the RelE toxin, an inhibitor of translation, caused a sharp increase in persisters. Functional expression of a putative HipA toxin also increased persisters, while deletion of the hipBA module caused a sharp decrease in persisters in both stationary and biofilm populations. HipA is thus the first validated persister-MDT gene. We suggest that random fluctuation in the levels of MDT proteins leads to the formation of rare persister cells. The function of these specialized dormant cells is to ensure the survival of the population in the presence of lethal factors.     

Enterotoxin formation by Clostridium perfringens type A studied by the use of fluorescent antibody.

Fluorescein isothiocyanate-conjugated antibody to purified enterotoxin of Clostridium perfringens was used to study the intracellular formation of enterotoxin by this organism. Enterotoxin was detected at 4 h of growth at the end of the cell containing forespore. With the development of the spore, enterotoxin accumulation continued and involved the entire length of the cell until its lysis with the release of enterotoxin and mature spore. The spores did not contain demonstrable enterotoxin. Only a certain number of the sporulated cells of the enterotoxigenic strains studied produced this toxin. The amount of enterotoxin produced varied with sporulation percentage, and between strains and individual cells.     

Zur Kenntnis der postmeiotischen Ereignisse der Samenentwicklung bei den Skarabäiden (Coleoptera)

Zusammenfassung Die postmeiotischen Ereignisse der Samenentwicklung wurden bei der Käferfamilie Scarabaeidae untersucht.Alle Geschlechtszellen einer Spermatozyste bilden während der Spermiohistogenese ein Bündel, das von einer aus den Zystenzellen stammenden und einer mit sog. Kopfzelle versehenen Plasmahülle umgeben ist. Die Samenzellen erreichen ihre aktive Beweglichkeit erstmalig im Bündelzustand im Hoden. Als erstes Zeichen der Aktivierung kommt eine verschiedene Färbbarkeit und oft eine eigene, gelbliche Farbe der Bündel zum Vorschein. Die Bündel sammeln sich in den zentralen Teilen des Hodens an, wo Sauerstoff am reichlichsten durch die Tracheenzweige des Samenleiters zugeführt wird.Eine große Mannigfaltigkeit herrscht betreffs der Entwicklung der Koplzelle, des Schicksals des bei der Spermiohistogenese beseitigten Zytoplasmas und des Eintritts der Samenzellen in den Samenleiter.Die phytophagen Skarabäiden und die Geotrupinen bilden eine ziemlich einheitliche Gruppe. Das beseitigte Zytoplasma ist knapp, die Koplzelle und die Hülle des Bündels schwach entwickelt. Das blinde Ende des Samenleiters wird in einem jungen Hoden zum erstenmal wahrscheinlich durch eine Aktivität der Spermienbündel durchbrochen, wonach der Weg zum Samenleiter beständig offen bleibt. Die Befreiung der Samenzellen aus der Bündelhülle erfolgt beim Eintreten in den Samenleiter. Die Hüllen werden ziemlich entfernt in den Windungen des Samenleiters abgebaut.Bei den meisten untersuchten Koprophagen entwickelt sich eine große Kopfzelle auf Kosten des ursprünglichen Zytoplasmas der Zystenzellen und des beseitigten Zytoplasmas der Spermatiden. Die Kopfzellen mit zugehörenden Bündelhüllen werden nach oder bei der Perforation des blinden Samenleiterendes abgeworfen. Sie bilden ein dichtes Gedränge im Samenleiter, wo sie bald abgebaut und resorbiert werden. Bei den Aphodius-Arten erfolgt die Resorption schon sofort im hodeninneren Teil des Samenleiters. Die Perforation des Samenzellenbündels scheint wenigstens bei den Aphodius-Arten ein aktiver Vorgang zu sein.Diese Untersuchung wurde ausgeführt mit Unterstützung des Finnischen Staates.     

Increased sister-chromatid exchange rate and its regression during prolonged incubation in lymphocyte cultures from patients with multiple sclerosis

Peripheral venous blood lymphocytes from multiple sclerosis patients, cultured for 72 h in the presence of phytohemagglutinin, appeared to have a higher sister-chromatid exchange (SCE) rate than cells from matched controls. Prolongation of the incubation time to 9 days by adding interleukin-2 to the cultures, caused the cells from the MS patients to lose their increased SCE frequency, so that the mean rate no longer differed from that of the controls. The SCE rate of the controls did not change significantly on prolonged incubation.     

A survey of Clostridium perfringens enterotoxin antibody in human and animal sera in western Canada

Sera from human, cattle, sheep, swine, and horse populations in western Canada were tested for the presence of Clostridium perfringens enterotoxin antibody by the passive hemagglutination (PHA) test, supplemented by an immunodiffusion test and by counterimmunoelectrophoresis. A total of 224 human, 345 cattle, 165 sheep, 620 swine, and 768 horse serum samples were examined. Low-titer reactions in the PHA test were detected in human, cattle, horse, and swine sera, in that order, with no titers demonstrated in sheep. The titers in human sera ranged up to 1:128 and three of these samples were also positive in the other two serological tests. The significance of this antibody is not clear, but it is suggested that the low prevalence of the antibody may reflect a low prevalence of enterotoxigenic C. perfringens strains in western Canada. Such serological surveys may be applicable to epidemiological studies involving enterotoxigenic C perfringens.     

Distribution of nuclear pores and perinuclear dense substances in spermatocytes I of some oedionychina fleabeetles

The nuclear envelope of growing postpachytene spermatocyte I differs notably in structure between the fleabeetles Omophoita cyanipennis and Oedionychus bicolor. The former species shows a more conventional structure with an even and probably random distribution of nuclear pores, and a strongly electron-opaque layer of fibrogranular material (FM) separated from the outer nuclear membrane by an intermediate layer of about 40 nm thickness. Peripherally from the FM layer, a continuous corona of granular dense material (GM) is accumulated around the nucleus. In Oedionychus, all nuclear pores are clustered in “nuclear sieves”, i.e., shallow, cup-like indentations of the nuclear envelope. The sieves are filled with an electron-opaque substance resembling the FM of the Omophoita spermatocytes. This substance is kept at a distance of about 40 nm from the outer nuclear membrane. GM is produced only at the sieves, and is thus discontinuous. The sieves with their contents are called nuclear sieve complexes (NSC).     

Efficacy of laboratory tests for the detection of enterotoxigenic Clostridium perfringens.

Nineteen Clostridium perfringens strains with positive erythemal and ligated intestinal loop reactions, and 22 strains with negative reactions, originating from food-poisoning cases, were tested comparatively using the fluorescent antibody (FA), reversed passive hemagglutination (RPHA), and immunodiffusion (ID) tests. All the biologically positive strains were detected by the three immunological tests used. The FA test detected five additional strains among the biologically negative group which did not react in RPHA or ID tests. Sporulating culture supernatant fluids, after 13 to 17h of growth, were satisfactory for testing for the presence of enterotoxin by the RPHA and ID tests. The FA test was used on cell smears.