An <Emphasis Type="Italic">Escherichia coli aer</Emphasis> mutant exhibits a reduced ability to colonize the streptomycin-treated mouse large intestine

The oxygen sensor Aer of Escherichia coli affects the expression level of genes that are involved in sugar acid degradation. Phenotypes of Aer mediated gene regulation, namely growth on sugar acids was tested ‘in vitro’ with Phenotype MicroArrays and colonization of the mouse large intestine was tested ‘in vivo’. The aer mutant did not grow on the sugar acids d-gluconate, d-glucuronate, d-galacturonate, as well as the sugar alcohol d-mannitol. Since sugar acids are the predominant carbon source for E. coli in the intestinal mucosa, the ability of the aer mutant to colonize the streptomycin-treated mouse large intestine was tested. The mutant exhibited a decreased ability to colonize the intestine when compared to wild-type cells. This effect was more pronounced under competitive conditions. The colonization phenotype of the aer mutant was complemented with either of two plasmids. One of them expressed the Aer protein, whereas the other one expressed the sugar acid degradation enzymes that are encoded by edd and eda. The data support the interpretation that decreased expression of edd and eda along with the decreased ability to grow on sugar acids may contribute to the reduced capacity of the aer mutant to colonize the mouse intestine. While Aer seems to be important during the initiation phase of colonization, FlhD/FlhC appears to be of disadvantage during maintenance phase. FlhD/FlhC is the master regulator of all flagellar genes and required for Aer expression. Mutants in flhD exhibited an initial competitive disadvantage during the first 3 days of colonization, but recovered lateron.     

Selective predation of the pike Esox lucius: comparison of lateral plates and some metric features of the three-spined stickleback Gasterosteus aculeatus

Selective predation of Esox lucius on Gasterosteus aculeatus in a natural assemblage of fish of a stream in Central Poland is described and analysed. The number of lateral plates, the standard length and four size-dependent traits were significantly smaller for sticklebacks from stomach samples than for those from population samples. Thc remaining three metric traits were not significantly different among the samples. The regressions of five metric features (out of seven) on the standard length were significantly different between the sample of caten sticklebacks and that from the free-living population. This supports the supposition that the selectivity of pikc predation with respect to metric traits is not attributable to selection on body size of the prey. Thus, it is reasonable to claim that the sample of caten sticklebacks is selectively taken from the natural population. It justifies the selective predation assumption of some hypotheses of the causes of the pattern of geographic variation in the three-spined stickleback.     

Pneumococcal Forssman antigen: enrichment in mesosomal membranes and specific binding to the autolytic enzyme of Streptococcus pneumoniae.

The choline-containing pneumococcal membrane teichoic acid (Forssman antigen) can be isolated with the membrane fractions of the bacteria. The small vesicle (mesosomal) fraction generated during the formation of protoplasts seems to be highly enriched in this material. Forssman antigen was identified in cell fractions on the basis of (i) radioactive choline label, (ii) autolysin-inhibitory activity, and (iii) the sedimentation profile in sucrose density gradients with and without detergent. A membrane teichoic acid could also be isolated from pneumococci grown in medium in which choline was replaced by ethanolamine as the nutritionally required amino alcohol. This material contained radioactive ethanolamine label and behaved similarly to the choline-containing membrane teichoic acid during centrifugation in detergent-containing and detergent-free density gradients. On the other hand, the material had only low autolysin-inhibitory activity. Binding of pure pneumococcal autolysin to micelles of purified Forssman antigen could be demonstrated by mixing these components in vitro and analyzing them by sucrose density gradients and by agarose chromatography. No binding could be observed between the pneumococcal enzyme and the micellar forms of either cardiolipin or polyglycerophosphate-type lipoteichoic acid isolated from Streptococcus lactis.     

THE FINE STRUCTURE AND MODE OF ATTACHMENT OF THE SHEATHED FLAGELLUM OF VIBRIO METCHNIKOVII

The sheathed flagellum of Vibrio metchnikovii was chosen for a study of the attachment of the flagellum to the bacterial cell. Normal and autolysed organisms and isolated flagella were studied by electron microscopy using the techniques of thin sectioning and negative staining. The sheath of the flagellum has the same layered structure as the cell wall of the bacterium, and in favourable thin sections it appears that the sheath is a continuation of the cell wall. After autolysis the sheath is usually absent and the core of the flagellum has a diameter of 120 A. Electron micrographs of autolysed bacteria negatively stained with potassium phosphotungstate show that the core ends in a basal disc just inside the plasma membrane. The basal disc is about 350 A in diameter and is thus considerably smaller than the "basal granules" described previously by other workers.     

A Commentary on the Need for 3D-Biologically Relevant In Vitro Environments to Investigate Astrocytes and Their Role in Central Nervous System Inflammation

Astrocytes execute essential functions in the healthy CNS, whilst also being implicated as a limitation to functional regeneration and repair after injury. They respond to injury to minimize damage to healthy tissue whilst also attempting to seal the broken blood-brain-barrier, however, they impede recovery if they are persistent and form a permanent scar in the injured brain. As such, it is of great importance to understand the mechanism underlying the astrocytic response to injury, and this understanding is currently limited by the in vitro environments available to scientists. Biomaterials such as nanofibres and hydrogels offer great potential for the development of superior, 3D cell culture environments in which to study astrocyte behavior and phenotype. The implementation of such in vitro environments with a particularly interdisciplinary approach can improve the field’s understanding of astrocytes, their role in central nervous system inflammation, and elucidate potential strategies to achieve functional regeneration.     

Effects of nitrous oxide inactivation of vitamin B12 and of methionine on folate coenzyme metabolism in rat liver, kidney, brain, small intestine and bone marrow

The effects of nitrous oxide inactivation of the vitamin B12-dependent enzyme, methionine synthetase (EC 2.1.1.13), and of methionine on folate coenzyme metabolism were determined in rat liver, kidney, brain, small intestine and bone marrow cells. Nitrous oxide exposure led to an increase in the proportion of 5-methyltetrahydrofolate at the expense of other reduced folates in all tissues examined. Administration of methionine at levels up to 400 mg/kg resulted in the normalization of folate coenzyme patterns in liver as a result of the increased levels of S-adenosylmethionine. In other tissues examined, methionine had no effect on the levels of S-adenosylmethionine or S-adenosylhomocysteine, or on the distribution of folate coenzymes. These results are consistent with the methyl trap hypothesis as the explanation of the relationship between vitamin B12 and folate metabolism, and provide direct evidence that the sparing effect of methionine on folate metabolism is a phenomenon restricted to the liver.     

Factors influencing the uptake of 14C-labelled Vibrio anguillarum vaccine in direct immersion experiments with rainbow trout, Salmo gairdneri Richardson

The factors influencing the uptake of a ¹⁴C-labelled Vibrio anguillarum vaccine in direct immersion experiments with rainbow trout, Salmo gairdneri were studied. Immersion times of longer than 10 s did not increase vaccine uptake. A pre-immersion dip in a hyperosmotic solution had no effect on uptake, even at lower vaccine bath concentrations. It appeared that the head end of the fish was implicated in uptake. Vaccine uptake decreased at lower temperatures, whereas the use of an adjuvanted vaccine and a soluble vaccine preparation led to increased uptake. Larger fish took up more vaccine.