A regulatory interaction between pyrimidine and purine biosyntheses via ureidosuccinic acid

Summary l-Ureidosuccinic acid (USA), an intermediate metabolite of pyrimidine biosynthesis, inhibits cell growth. Mutants blocked in pyrimidine biosynthesis after dihydroorotate (DHO), are more resistant to USA than are the wild type and the mutants blocked in the synthesis of DHO. This difference in sensitivity correlates with the level of dihydroorotase activity. Purines revert USA inhibition. Mutants selected for their resistance to USA were resistant because of a) overproducing purines (adenine excretion), b) having a reduced USA uptake, or c) showing a USA resistance independant of the above phenotypes.     

保加利亚乳杆菌微胶囊化工艺研究

目的制备保加利亚乳杆菌微胶囊,提高菌株的酸、热耐受性及降低菌体的分离成本。方法以保加利亚乳杆菌(Lactobacillus bulgaricus)为研究对象,海藻酸钠(SA)为壳材、CaCl2为固化剂,制备保加利亚乳杆菌微胶囊;包埋率、颗粒平均化程度、机械强度等为考核指标,研究保加利亚乳杆菌微胶囊化的工艺。结果当海藻酸钠浓度为0.75%、CaCl2浓度为3%、电压为600V、泵速为1.96mL/min、震动频率为80Hz时,微胶囊化包埋效果最佳,经固定化后的菌微胶囊保持了良好的保加利亚乳杆菌的活性,微囊化保加利亚乳杆菌经过2次连续发酵后的产酸量分别达到59.4g/L和55.8g/L。结论本研究为工业化生产乳酸提供了一条具有经济价值的途径。     

Lactic acid production by mixed cultures of Kluyveromyces marxianus, Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus helveticus

Lactic acid production using Kluyveromyces marxianus (IFO 288), Lactobacillus delbrueckii ssp. bulgaricus (ATCC 11842) and Lactobacillus helveticus (ATCC 15009) individually or as mixed culture on cheese whey in stirred or static fermentation conditions was evaluated. Lactic acid production, residual sugar and cell biomass were the main features examined. Increased lactic acid production was observed, when mixed cultures were used in comparison to individual ones. The highest lactic acid concentrations were achieved when K. marxianus yeast was combined with L. delbrueckii ssp. bulgaricus, and when all the strains were used revealing possible synergistic effects between the yeast and the two lactic acid bacteria. The same synergistic effects were further observed and verified when the mixed cultures were applied in sourdough fermentations, proving that the above microbiological system could be applied in the food fermentations where high lactic acid production is sought.     

Transfection of Lactobacillus bulgaricus protoplasts by bacteriophage DNA

A protoplast transfection system has been developed for Lactobacillus bulgaricus. The procedure involves a polyethylene glycol-mediated fusion of bacteriophage DNA encapsulated in liposomes into mutanolysin-treated cells. With L. bulgaricus B004 and DNA isolated from the phage phi c5004, transfection reached a maximum when at least 95% of the cells were osmotically fragile. The incorporation of phage DNA into liposomes was essential; no transfectants were detected in the absence of liposomes. The largest number of transfectants was observed after longer periods (20 min) of fusion of mutanolysin-treated cells and liposomes with polyethylene glycol. The maximum efficiency of 5 x 10(7) PFU/microgram of DNA was reached after a 24-h incubation in growth media prior to plating transfected cells in an agar overlay to detect the appearance of plaques. A minimum of 4 h of incubation in growth medium after fusion was required to detect the production and release of virions. The possibility that the high frequencies observed were due to bursting of transfected cells and subsequent infection of additional cells was found not to be a factor. The number of transfectants observed was directly proportional to the quantity of DNA added. These results define conditions appropriate for the introduction of DNA into L. bulgaricus.     

Semi-continuous lactic fermentation of whey by Lactobacillus bulgaricus

Semi-continuous tests of lactic fermentation of whey by Lactobacillus buigaricus were carried out using a mixture of hydrolysed milk and vitamins. The volume of the Inoculum varied from 20% to 50% of the reactor working volume. A Monod-like equation correlates the lactic acid productivity and the volume fraction of inoculum.The authors are with the Centro de Desenvolvimento Biotecnológico de Santa Catarina (Biotechnological Development Centre of Santa Catarina), R. Princesa isabel, 114, 89200, Joinville, SC, Brazil. CDEB. L.A. Kulay was an undergraduate student, in 1989, of the Escola de Engenharia Mauá (Mauá Engineering School), São Caetano do Sul, SP, Brazil. W. Borzani is the corresponding author.     

Exopolysaccharides production in Lactobacillus bulgaricus and Lactobacillus casei exploiting microfiltration

The physiology of Lactobacillus delbrueckii ssp. bulgaricus and Lactobacillus casei, extensively used in the dairy industry, was studied in order to evaluate key parameters in the synthesis of exopolysaccharides and to improve their production through novel fermentation processes. Selected strains were studied in shake flasks and in fermentor experiments using glucose and lactose as main carbon sources and bacto casitone as the only complex component, in a temperature range between 35 and 42°C. The production of exopolysaccharides was monitored and correlated to the growth conditions using both a colorimetric assay and chromatographic methods. Fermentor experiments in batch mode yielded 100 mg l⁻¹ of EPS from L. bulgaricus and 350 mg l⁻¹ from L. casei. Moreover, the use of a microfiltration (MF) bioreactor resulted in exopolysaccharides (EPS) concentrations threefold and sixfold those of batch experiments, respectively. The monosaccharidic composition of the two analyzed polymers differed from those previously reported. The optimization of the production of EPSs using the MF fermentation strategy could permit the use of these molecules produced by generally recognised as safe (GRAS) microorganisms in the place of other polysaccharides in the food industry.     

The synthesis of folic acid-like compounds by Lactobacillus arabinosus

In the presence of p-aminobenzoic acid (PABA), Lactobacillus arabinosus synthesizes one or more compounds with folic acid (FA)-like activity during growth. The total FA activity formed is proportional to the amount of PABA added, up to 200 mμg./tube. Most of the FA activity is in a bound form which is present chiefly in the cells, and the remainder is present in free form which is mainly in the culture medium. Increasing levels of sulfanilamide in the medium competitively inhibit the utilization of PABA for growth of L. arabinosus and decrease the amount of free and combined FA compounds formed.Equimolecular amounts of p-aminobenzoylglutamic acid and PABA have approximately the same growth-promoting and antisulfanilamide activities for L. arabinosus under the conditions employed, and lead to the synthesis of similar amounts of the FA-like compound by L. arabinosus.Thymidine can replace PABA for growth of L. arabinosus and its activity is inhibited very little by sulfanilamide. Thymine and thymidylic acid are much less effective than thymidine. Crystalline vitamin B_c conjugate and vitamin B₁₂ cannot replace PABA for growth of L. arabinosus and do not augment the antisulfonamide activity of PABA.The growth-promoting and antisulfanilamide activities of synthetic folid acid (pteroylglutamic acid), citrovorum factor, and formylfolic acid preparations for L. arabinosus are much poorer than those of equimolecular amounts of PABA. The possibility that the compound(s) with FA-like activity produced by L. arabinosus may differ from pteroylglutamic acid, citrovorum factor, or formylfolic acid is discussed.     

Efficient synthesis and biological evaluation of epiceanothic acid and related compounds

Epiceanothic acid (1) is a naturally occurring, but very rare pentacyclic triterpene with a unique pentacyclic triterpene (PT) structure. An efficient synthesis of 1 starting from betulin (3) has been accomplished in 12-steps with a total yield of 10% in our study. Compound 1 and selected synthetic intermediates were further evaluated as anti-HIV-1 agents, inhibitors of glycogen phosphorylase (GP), and cytotoxic agents. Compound 1 exhibited moderate HIV-1 inhibition. Most importantly, compound 5, with an opened A-ring, showed significant GP inhibitory activity with an IC₅₀ of 0.21 μM, suggesting a potential for development as an anti-diabetic agent. On the other hand, compound 12, with a closed A-ring, showed potent cytotoxicity against A549 and MCF-7 human tumor cell lines, with IC₅₀ values of 0.89 and 0.33 μM, respectively. These results suggest that the A-ring of PTs is an important pharmacophore that could be modified to involve different biological activities.