RESUMEN
Curdlan is a bacterial, water-insoluble, linear homopolysaccharide that has been widely used in the food industry. In this study, genome information of strain CGMCC 11546, a UV-induced high-yield mutant of the model curdlan-producing strain Agrobacterium sp. ATCC 31749, was used to investigate the molecular mechanism of curdlan biosynthesis. The maximum curdlan yield of 47.97 ± 0.57 g/L was obtained from strain CGMCC 11546 by using optimal media containing 60 g/L sucrose, 6 g/L yeast, 2 g/L KH2PO4, 0.4 g/L MgSO4·7H2O, 2 g/L CaCO3, 0.1 g/L FeSO4·7H2O, 0.04 g/L MnSO4, and 0.02 g/L ZnCl2 at 30 °C and 280 rpm after 96 h of fermentation. The gel strength of curdlan was improved by 41 % by knocking out the ß-1,3-glucanase genes exoK and exsH of strain CGMCC 11546. Furthermore, the application of curdlan from the ΔexoK-exsH strain in noodles significantly improved the eating quality of both raw and cooked noodles.
Asunto(s)
Agrobacterium/enzimología , Agrobacterium/genética , Genoma Bacteriano , Polisacáridos Bacterianos/metabolismo , beta-Glucanos/metabolismo , Agrobacterium/efectos de la radiación , Proteínas Bacterianas/genética , Medios de Cultivo/química , Suplementos Dietéticos , Fermentación , Calidad de los Alimentos , Geles/química , Eliminación de Gen , Glucano 1,3-beta-Glucosidasa/genética , Peso Molecular , Organismos Modificados Genéticamente , Rayos Ultravioleta , Secuenciación Completa del Genoma/métodosRESUMEN
Prokaryotic (6-4) photolyases branch at the base of the evolution of cryptochromes and photolyases. Prototypical members contain an iron-sulphur cluster which was lost in the evolution of the other groups. In the Agrobacterium (6-4) photolyase PhrB, the repair of DNA lesions containing UV-induced (6-4) pyrimidine dimers is stimulated by Mg2+ . We propose that Mg2+ is required for efficient lesion binding and for charge stabilization after electron transfer from the FADH- chromophore to the DNA lesion. Furthermore, two highly conserved Asp residues close to the DNA-binding site are essential for the effect of Mg2+ . Simulations show that two Mg2+ bind to the region around these residues. On the other hand, DNA repair by eukaryotic (6-4) photolyases is not increased by Mg2+ . In these photolyases, structurally overlapping regions contain no Asp but positively charged Lys or Arg. During the evolution of photolyases, the role of Mg2+ in charge stabilization and enhancement of DNA binding was therefore taken over by a postiviely charged amino acid. Besides PhrB, another prokaryotic (6-4) photolyase from the marine cyanobacterium Prochlorococcus marinus, PromaPL, which contains no iron-sulphur cluster, was also investigated. This photolyase is stimulated by Mg2+ as well. The evolutionary loss of the iron-sulphur cluster due to limiting iron concentrations can occur in a marine environment as a result of iron deprivation. However, the evolutionary replacement of Mg2+ by a positively charged amino acid is unlikely to occur in a marine environment because the concentration of divalent cations in seawater is always sufficient. We therefore assume that this transition could have occurred in a freshwater environment.
Asunto(s)
Agrobacterium/enzimología , Ácido Aspártico/química , Proteínas Bacterianas/química , Reparación del ADN/efectos de los fármacos , Desoxirribodipirimidina Fotoliasa/química , Magnesio/fisiología , Agrobacterium/genética , Agrobacterium/efectos de la radiación , Proteínas Bacterianas/genética , Proteínas Bacterianas/metabolismo , Sitios de Unión , Simulación por Computador , ADN/efectos de la radiación , Desoxirribodipirimidina Fotoliasa/genética , Desoxirribodipirimidina Fotoliasa/metabolismo , Proteínas de Drosophila/química , Células Eucariotas/enzimología , Evolución Molecular , Flavina-Adenina Dinucleótido/metabolismo , Agua Dulce , Magnesio/farmacología , Modelos Moleculares , Mutación Missense , Filogenia , Prochlorococcus/enzimología , Células Procariotas/enzimología , Unión Proteica/efectos de los fármacos , Conformación Proteica , Dímeros de Pirimidina/metabolismo , Rayos UltravioletaRESUMEN
To determine the synergistic disinfection effect of the combined treatments of sodium hypochlorite (NaClO), irradiation, and vitamin B(1), the bactericidal effects of the treatments on natural microflora of oyster and short-necked clam were investigated. Then, bacteria isolated from the samples were identified by 16S rDNA sequencing. Oyster and short-necked clam were mainly contaminated with Vibrio spp. and Bacillus spp. Total number of aerobic bacteria ranged from 10(2) to 10(4) colony forming units (CFU)/g initially. More than 100 mg/L of NaClO with 1000 mg/L vitamin B(1) and 2 kGy irradiation treatment for oyster and short-necked clam can reduce the total aerobic bacteria to the level of lower than a detection limit (10 CFU/g). Synergistic effects were observed for all combined treatment against natural microflora. The results suggest that a significant synergistic benefit can be achieved by a combination of NaClO-ionizing radiation treatment with the addition of vitamin B(1) to reduce the microbial population contaminated in oyster and short-necked clam.
