A new κ-carrageenase gene cgkS was cloned from marine bacterium Shewanella sp. Kz7 by using degenerate and site-finding PCR. The gene was comprised of an open reading frame of 1224bp, encoding 407 amino acid residues...A new κ-carrageenase gene cgkS was cloned from marine bacterium Shewanella sp. Kz7 by using degenerate and site-finding PCR. The gene was comprised of an open reading frame of 1224bp, encoding 407 amino acid residues, with a signal peptide of 24 residues. Based on the deduced amino acid sequence, the κ-carrageenase CgkS was classified into the Glycoside Hy- drolase family 16. The cgkS gene was expressed in Escherichia coli, and the recombinant enzyme was purified to homogeneity with a specific activity of 716.8 U mg-1 and a yield of 69%. Recombinant CgkS was most active at 45 ℃ and pH 8.0. It was stable at pH 6.0-9.0 and below 30℃. The enzyme did not require NaCl for activity, although its activity was enhanced by NaCI. CgkS degraded κ-carrageenan in an endo-fashion releasing tetrasaccharides and disaccharides as main hydrolysis products.展开更多
Bactericidal activity of some arginine based biodegradable polymers-PEURs （poly （ester urethane）s） and PEUs （poly （ester urea）s） with low cytotoxicity was studied in in vitro experiments. Various bacterial str...Bactericidal activity of some arginine based biodegradable polymers-PEURs （poly （ester urethane）s） and PEUs （poly （ester urea）s） with low cytotoxicity was studied in in vitro experiments. Various bacterial strains both Gram-positive and Gram-negative were used to explore the bactericidal activity of the cationic polymers. As the test objects, the following microorganisms were used： Bacillus subtilis, Staphylococcus aureus, Mycobacterium album, Pseudomonas fluorescens, Escherichia coli, Actinomyces griseus and Aspergillus niger. The obtained results showed that the new cationic polymers suppressed the growth of the studied microorganisms and the bactericidal activity of the tested cationic polymers strongly depending on their chemical structure.展开更多
To evaluate the role of bacterial symbionts ( Buchnera spp. ) in the black bean aphids ( Aphis craccivora Koch), the aphids were treated with the antibiotic, rifampicin, to eliminate their intracellular symbiotic bact...To evaluate the role of bacterial symbionts ( Buchnera spp. ) in the black bean aphids ( Aphis craccivora Koch), the aphids were treated with the antibiotic, rifampicin, to eliminate their intracellular symbiotic bacteria. Analysis of protein and amino acid concentration in 7-day-old of aposymbiotic aphids showed that the total protein content per mg fresh weight was significantly reduced by 29 %, but free amino acid titers were increased by 17% . The ratio of the essential amino acids was in general only around 20% essential amino acids in phloem sap of broad bean, whereas it was 44% and 37% in symbiotic and aposymbiotic aphids, respectively,suggesting that the composition of the free amino acids was unbalanced. For example, the essential amino acid,threonine represented 21. 6% of essential amino acids in symbiotic aphids, but it was only 16.7% in aposymbiotic aphids. Likewise, two nonessential amino acids, tyrosine and serine, represented 8.9% and 5.6% of total amino acids in symbiontic aphids, respectively, but they enhanced to 21.1% and 13.6% in aposymbiotic aphids. It seems likely that the elevated free amino acid concentration in aposymbiotic aphids was caused by the limited protein anabolism as the result of the unbalanced amino acid composition.展开更多
基金supported by the Key Technologies Research and Development Program of China(2013BA B01B02)National Science Foundation of China(310707 12)+1 种基金Special Fund for Marine Scientific Research in the Public Interest(201005024 and 201105027)National Hightech R&D Program of China(2011AA09070304)
文摘A new κ-carrageenase gene cgkS was cloned from marine bacterium Shewanella sp. Kz7 by using degenerate and site-finding PCR. The gene was comprised of an open reading frame of 1224bp, encoding 407 amino acid residues, with a signal peptide of 24 residues. Based on the deduced amino acid sequence, the κ-carrageenase CgkS was classified into the Glycoside Hy- drolase family 16. The cgkS gene was expressed in Escherichia coli, and the recombinant enzyme was purified to homogeneity with a specific activity of 716.8 U mg-1 and a yield of 69%. Recombinant CgkS was most active at 45 ℃ and pH 8.0. It was stable at pH 6.0-9.0 and below 30℃. The enzyme did not require NaCl for activity, although its activity was enhanced by NaCI. CgkS degraded κ-carrageenan in an endo-fashion releasing tetrasaccharides and disaccharides as main hydrolysis products.
文摘Bactericidal activity of some arginine based biodegradable polymers-PEURs （poly （ester urethane）s） and PEUs （poly （ester urea）s） with low cytotoxicity was studied in in vitro experiments. Various bacterial strains both Gram-positive and Gram-negative were used to explore the bactericidal activity of the cationic polymers. As the test objects, the following microorganisms were used： Bacillus subtilis, Staphylococcus aureus, Mycobacterium album, Pseudomonas fluorescens, Escherichia coli, Actinomyces griseus and Aspergillus niger. The obtained results showed that the new cationic polymers suppressed the growth of the studied microorganisms and the bactericidal activity of the tested cationic polymers strongly depending on their chemical structure.
文摘To evaluate the role of bacterial symbionts ( Buchnera spp. ) in the black bean aphids ( Aphis craccivora Koch), the aphids were treated with the antibiotic, rifampicin, to eliminate their intracellular symbiotic bacteria. Analysis of protein and amino acid concentration in 7-day-old of aposymbiotic aphids showed that the total protein content per mg fresh weight was significantly reduced by 29 %, but free amino acid titers were increased by 17% . The ratio of the essential amino acids was in general only around 20% essential amino acids in phloem sap of broad bean, whereas it was 44% and 37% in symbiotic and aposymbiotic aphids, respectively,suggesting that the composition of the free amino acids was unbalanced. For example, the essential amino acid,threonine represented 21. 6% of essential amino acids in symbiotic aphids, but it was only 16.7% in aposymbiotic aphids. Likewise, two nonessential amino acids, tyrosine and serine, represented 8.9% and 5.6% of total amino acids in symbiontic aphids, respectively, but they enhanced to 21.1% and 13.6% in aposymbiotic aphids. It seems likely that the elevated free amino acid concentration in aposymbiotic aphids was caused by the limited protein anabolism as the result of the unbalanced amino acid composition.
