Phosphoglucose isomerase (PGI) is a key enzyme in early glycolysis, which catalyzes the reversible isomerization of glucose 6-phosphate (G6Ph) to fructose 6-phosphate. We have constructed an Escherichia coli K12 strai...Phosphoglucose isomerase (PGI) is a key enzyme in early glycolysis, which catalyzes the reversible isomerization of glucose 6-phosphate (G6Ph) to fructose 6-phosphate. We have constructed an Escherichia coli K12 strain with a deleted pgi gene (Δpgi) and shown that this strain in comparison with the parental strain 1) accumulates higher amount of G6Ph, 2) grows slowly, and 3) exhibits higher spontaneous mutation frequency to rifampicin resistance (Rifr), when grown on high glucose minimal medium. Intriguingly, the spontaneous mutation rate to Rifr was inversely related to the degree of E. coli chromosomal DNA modification with sugar derivatives. We measured higher concentrations of Amadori products, fluorophores (360 nm excitation/440 nm emission) and carboxymethyl residues in the chromosomal DNA of the E. coli parental strain than in DNA of the isogenic Δpgi strain. To explain this apparent paradox we hypothesized that PGI might be implicated in repair of G6Ph-derived lesions in DNA. In favor of our hypothesis, we further demonstrate that protein extract from the E. coli PGI proficient strain but not from the PGI deficient strain catalyzes the release of G6Ph from G6Ph-modified single stranded DNA oligonucleotide and from its hybrid duplex with a complementary peptide nucleic acid.展开更多
The strains ofLactobacillus delbrueckii subsp, lactis widely used in food preservation due to ability produce high amount of hydrogen peroxide at refrigerator temperatures to inhibit food-borne pathogens and psychroph...The strains ofLactobacillus delbrueckii subsp, lactis widely used in food preservation due to ability produce high amount of hydrogen peroxide at refrigerator temperatures to inhibit food-borne pathogens and psychrophilic spoilage microorganisms. In order to improve of bio-preservation efficacy ofL. delbrueckii MH 10 mutations causing resistance to streptomycin （str） were used. Among UV-mutagenized population of L. delbruecla＇i three str mutants producing high amounts of H2O2 were selected. Sir mutants produced significant amounts of hydrogen peroxide 50-60 μg/ml in sodium phosphate buffer （0.2 M, pH 6.5） and in beef broth （BB） at 5 ℃ for 5 days submerged cultivation without of growth. Evaluation mutants antibacterialactivity at refrigeration temperatures against food-borne pathogen Escherichia coli O157：H7 revealed elimination of pathogen total number up to practically undetectable amount for 3 days. In case of solid-state cultivation on agar-based medium, disks soaked by mutant cells suspensions formed larger inhibitory zones on E. coli O157：H7 lawn for one-day cold exposition. The size of inhibition zone depends on concentration of LAB cells. Str mutants L. delbrueckii reduced initial amount 2 - 105 of E. coil O 157：H7 in ground beef up to 3 log for 3 days of solid-state cocultivation when the wild strain reduced only 2 log. The application ofL. delbrueckii mutants did not cause any changes in sensory characteristics of ground beef, moreover promotes expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.展开更多
为了研究高压静电场(HVEF)对大肠杆菌(E.coli)的损伤效应,采用不同处理条件的HVEF处理E.coli,考察了菌体的存活率、突变率及形态损伤。结果表明:在不同处理条件下,E.coli存活率和突变率均呈振荡型变化,且2者呈负相关,在4 k V/cm×2 ...为了研究高压静电场(HVEF)对大肠杆菌(E.coli)的损伤效应,采用不同处理条件的HVEF处理E.coli,考察了菌体的存活率、突变率及形态损伤。结果表明:在不同处理条件下,E.coli存活率和突变率均呈振荡型变化,且2者呈负相关,在4 k V/cm×2 min的处理条件下存活率最低,仅为(7.77±1.73)%,突变率达最高,为(13.73±1.99)×10-6,说明HVEF对菌体的存活具有抑制和激活的双重作用,在抑制作用下,细胞受到的损伤较大且相应的突变率也较高;通过电镜观察,发现HVEF作用下E.coli细胞膜破损并伴随有细胞内容物的溢出,说明高压静电场可有效破坏细胞的膜结构;通过测量HVEF在同一场强不同处理时间作用下菌液的核酸和蛋白质含量变化,发现上述2个参数在电场作用下也呈振荡型变化,说明适当的电场处理条件可调控菌体细胞膜的通透性,且在适当的电场处理条件下E.coli自身可能具有损伤修复功能。展开更多
文摘Phosphoglucose isomerase (PGI) is a key enzyme in early glycolysis, which catalyzes the reversible isomerization of glucose 6-phosphate (G6Ph) to fructose 6-phosphate. We have constructed an Escherichia coli K12 strain with a deleted pgi gene (Δpgi) and shown that this strain in comparison with the parental strain 1) accumulates higher amount of G6Ph, 2) grows slowly, and 3) exhibits higher spontaneous mutation frequency to rifampicin resistance (Rifr), when grown on high glucose minimal medium. Intriguingly, the spontaneous mutation rate to Rifr was inversely related to the degree of E. coli chromosomal DNA modification with sugar derivatives. We measured higher concentrations of Amadori products, fluorophores (360 nm excitation/440 nm emission) and carboxymethyl residues in the chromosomal DNA of the E. coli parental strain than in DNA of the isogenic Δpgi strain. To explain this apparent paradox we hypothesized that PGI might be implicated in repair of G6Ph-derived lesions in DNA. In favor of our hypothesis, we further demonstrate that protein extract from the E. coli PGI proficient strain but not from the PGI deficient strain catalyzes the release of G6Ph from G6Ph-modified single stranded DNA oligonucleotide and from its hybrid duplex with a complementary peptide nucleic acid.
文摘The strains ofLactobacillus delbrueckii subsp, lactis widely used in food preservation due to ability produce high amount of hydrogen peroxide at refrigerator temperatures to inhibit food-borne pathogens and psychrophilic spoilage microorganisms. In order to improve of bio-preservation efficacy ofL. delbrueckii MH 10 mutations causing resistance to streptomycin （str） were used. Among UV-mutagenized population of L. delbruecla＇i three str mutants producing high amounts of H2O2 were selected. Sir mutants produced significant amounts of hydrogen peroxide 50-60 μg/ml in sodium phosphate buffer （0.2 M, pH 6.5） and in beef broth （BB） at 5 ℃ for 5 days submerged cultivation without of growth. Evaluation mutants antibacterialactivity at refrigeration temperatures against food-borne pathogen Escherichia coli O157：H7 revealed elimination of pathogen total number up to practically undetectable amount for 3 days. In case of solid-state cultivation on agar-based medium, disks soaked by mutant cells suspensions formed larger inhibitory zones on E. coli O157：H7 lawn for one-day cold exposition. The size of inhibition zone depends on concentration of LAB cells. Str mutants L. delbrueckii reduced initial amount 2 - 105 of E. coil O 157：H7 in ground beef up to 3 log for 3 days of solid-state cocultivation when the wild strain reduced only 2 log. The application ofL. delbrueckii mutants did not cause any changes in sensory characteristics of ground beef, moreover promotes expanding of shelf-life due to inhibition of psychrophilic spoilage microorganisms.
文摘为了研究高压静电场(HVEF)对大肠杆菌(E.coli)的损伤效应,采用不同处理条件的HVEF处理E.coli,考察了菌体的存活率、突变率及形态损伤。结果表明:在不同处理条件下,E.coli存活率和突变率均呈振荡型变化,且2者呈负相关,在4 k V/cm×2 min的处理条件下存活率最低,仅为(7.77±1.73)%,突变率达最高,为(13.73±1.99)×10-6,说明HVEF对菌体的存活具有抑制和激活的双重作用,在抑制作用下,细胞受到的损伤较大且相应的突变率也较高;通过电镜观察,发现HVEF作用下E.coli细胞膜破损并伴随有细胞内容物的溢出,说明高压静电场可有效破坏细胞的膜结构;通过测量HVEF在同一场强不同处理时间作用下菌液的核酸和蛋白质含量变化,发现上述2个参数在电场作用下也呈振荡型变化,说明适当的电场处理条件可调控菌体细胞膜的通透性,且在适当的电场处理条件下E.coli自身可能具有损伤修复功能。
