Inducible reactivation of UV-irradiated cholera phage e5 in Vibrio cholerae MAK757

Summary The survival of UV-irradiated cholera phage e5 was found to increase when the host cells, Vibrio cholerae MAK757, were exposed to a low dose of UV irradiation before phage infection (Weigle reactivation), indicating the existence of a UV-inducible DNA repair pathway (SOS repair) in V. cholerae MAK757. The induction signal generated by UV irradiation was transient in nature and lasted about 20–30 min at 37°C. Maximal weigle reactivation of the phage was obtained when the host cells were irradiated with a UV dose of 16 J/m². V. cholerae MAK757 was also found to possess efficient photoreactivation and host cell reactivation of UV-damaged DNA in phage e5.     

Regulation of fructose uptake and catabolism by succinate in Azospirillum brasilense.

Fructose uptake and catabolism in Azospirillum brasilense is dependent on three fructose-inducible enzymes (fru-enzymes): (i) enzyme I and (ii) enzyme II of the phosphoenolpyruvate:fructose phosphotransferase system and (iii) 1-phosphofructokinase. In minimal medium containing 3.7 mM succinate and 22 mM fructose as sources of carbon, growth of A. brasilense was diauxic, succinate being utilized in the first phase of growth and fructose in the second phase with a lag period between the two growth phases. None of the fru-enzymes could be detected in cells grown with succinate as the sole source of carbon, but they were detectable toward the end of the first phase of diauxie. All the fru-enzymes were coinduced by fructose and coordinately repressed by succinate. Studies on the effect of succinate on differential rates of syntheses of the fru-enzymes revealed that their induced syntheses in fructose minimal medium were subject to transient as well as permanent (catabolite) repression by succinate. Succinate also caused a similar pattern of transient and permanent repression of the fructose transport system in A. brasilense. However, no inducer (fructose) exclusionlike effect was observed as there was no inhibition of fructose uptake in the presence of succinate with fructose-grown cells even when they were fully induced for succinate uptake activity.     

Continuous ethanol production in an immobilized whole cell fermenter using untreated sugar cane bagasse as carrier

Summary Saccharomyces cerevisiae was immobilised by adsorption to untreated sugar cane bagasse in a packed bed reactor. Complete conversion of glucose to ethanol was obtained at a dilution rate of 0.19 h⁻¹. Continuous ethanol production was maintained for up to 57 days. Reactor productivity increased with increasing packing density of the bagasse. Plugging of void spaces due to cell overgrowth led to channelling of the feed and decreased reactor productivity. Increasing the average column temperature alleviated plugging and restored column performance over a short period; however prolonged exposure to the high temperature resulted in decreased ethanol production rates. Bagasse has advantages as a support material for ethanol production from sugar cane or beet, including negligible cost, ready availability and the capacity to support a high yeast population.     

Characterization of three-fraction mycobacillin synthetase.

Mycobacillin synthetase lacks aspartic acid racemase, alanine racemase and glutamic acid racemase activities. The enzyme also does not respond to ATP-[32P]Pi exchange, nor does it catalyse the antibiotic synthesis in presence of amino acids of configuration opposite to that present in the molecule. Preincubation with optical isomers of opposite configuration inhibited the ATP-[32P]Pi exchange reaction to the extent of 60-90%. None of the three fractions of mycobacillin synthetase contained a pantothenic acid arm. Two molecules of ATP are required to synthesize one peptide bond of mycobacillin. Intermediate peptides of mycobacillin are not covalently linked to the three-fraction mycobacillin synthetase.     

Gill microcirculation of the air-breathing climbing perch, Anabas testudineus (Bloch):relationships with the accessory respiratory organs and systemic circulation

The general macrocirculation and branchial microcirculation of the air-breathing climbing perch, Anabas testudineus, was examined by light and scanning electron microscopy of vascular corrosion replicas. The ventral aorta arises from the heart as a short vessel that immediately bifurcates into a dorsal and a ventral branch. The ventral branch distributes blood to gill arches 1 and 2, the dorsal branch to arches 3 and 4. The vascular organization of arches 1 and 2 is similar to that described for aquatic breathing teleosts. The respiratory lamellae are well developed but lack a continuous inner marginal channel. The filaments contain an extensive nutritive and interlamellar network; the latter traverses the filament between, but in register with, the inner lamellar margins. Numerous small, tortuous vessels arise from the efferent filamental and branchial arteries and anastomose with each other to form the nutrient supply for the filament, adductor muscles, and arch supportive tissues. The efferent branchial arteries of arches 1 and 2 supply the accessory air-breathing organs. Arches 3 and 4 are modified to serve primarily as large-bore shunts between the dorsal branch of the ventral aorta and the dorsal aorta. In many filaments from arches 3 and 4, the respiratory lamellae are condensed and have only 1-3 large channels. In some instances in arch 4, shunt vessels arise from the afferent branchial artery and connect directly with the efferent filamental artery. The filamental nutrient and interlamellar systems are poorly developed or absent. The respiratory and systemic pathways in Anabas are arranged in parallel. Blood flows from the ventral branch of the ventral aorta, through gill arches 1 and 2, into the accessory respiratory organs, and then returns to the heart. Blood, after entering the dorsal branch of the ventral aorta, passes through gill arches 3 and 4 and proceeds to the systemic circulation. This arrangement optimizes oxygen delivery to the tissues and minimizes intravascular pressure in the branchial and air-breathing organs. The efficiency of this system is limited by the mixing of respiratory and systemic venous blood at the heart.     

Metabolic concomitants in pure, pancreatic beta cells during glucose-stimulated insulin secretion

The role of the redox potential in insulin secretion by beta cells stimulated with high glucose was investigated using an in vitro pancreas perfusion system. To assess glycolytic flux the sum of fructose-1,6-P2 + triose-P was determined in pure beta cells microdissected from lyophilized sections of the isolated perfused pancreas quick frozen during the early insulin secretory response. L-Glycerol 3-phosphate and dihydroxyacetone phosphate were measured as indicators of the free cytosolic [NAD+]/[NADH] ratio and NADH and NADPH were also measured. Fructose-1,6-P2 + triose-P was increased in beta cells simultaneously with the onset of insulin secretion indicating an increase in glucose metabolism had occurred. The ratio of [dihydroxyacetone phosphate]/[L-glycerol 3-phosphate] increased simultaneously with the onset of insulin secretion. NADH content increased only after initiation of insulin secretion and NADPH levels remained unchanged during the early secretory response to high glucose. These data contradict the hypothesis that insulin secretion is triggered by a more reduced cytosolic redox state and instead indicate that insulin secretion is initiated by other metabolic coupling factor(s) generated in beta cells stimulated by high glucose.     

Pollen-pistil interaction in Linum grandiflorum

A detailed investigation of the receptive surface of the stigma of a dimorphic taxon, Linum grandiflorum, was carried out using scanning electron microscopy, cytochemistry and polyacrylamide gel electrophoresis. The stigma surfaces of the pin and thrum morphs showed distinct differences. The stigma of the pin morph was of the dry type and the papillae were covered with a uniform cuticle-pellicle layer. The stigma of the thrum morph, on the other hand, resembled the wet type; the cuticle-pellicle layer was disrupted at places and a secretion product was released onto the surface of the stigma. Coomassie blue staining material was present on the surface of only the thrum stigma. Although esterases and acid phosphatases were present on the stigma of both the morphs, their activity was invariably higher on the thrum stigma. Polyacrylamide gel electrophoresis of stigma leachates also showed distinct differences in the protein profiles of the two morphs.