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Institut für Lebensmittelwissenschaft und Biotechnologie

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Browsing Institut für Lebensmittelwissenschaft und Biotechnologie by Subject "Acylneuraminsäuren"

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    Molekularbiologische und physiologische Untersuchungen zur Bedeutung phagenkodierter Sialinsäureesterasen von enterohämorrhagischen Escherichia coli (EHEC)
    (2019) Saile, Nadja; Schmidt, Herbert
    Enterohemorrhagic Escherichia coli (EHEC) are responsible for severe disease in humans such as hemorrhagic colitis or the life-threatening hemolytic uremic syndrome. The main virulence factors are Shiga toxins (Stx) and a type-III-secretion system. For colonization of the colon, they have to compete with the intestinal microbiota for limiting substrates such as 5-N-acetyl neuraminic acid (Neu5Ac). For the catabolism of Neu5Ac, E. coli possess the genes nanA, nanT, nanE, nanK, nagA, and nagB. Many sialic acids are terminally bound to mucins of mucus in the colon. E. coli is not able to use bound Neu5Ac, because it cannot express sialidases for cleavage of Neu5Ac from mucin. However, sialic acids can be cleaved by sialidases from anaerobic bacteria in the colon and are then available. Many E. coli strains encode the nanCMS operon. NanC is a porin protein, NanM is a mutarotase and NanS is an O-acetyl esterase. NanS converts 5-N-acetyl-9-O-acetyl neuraminic acid (Neu5,9Ac2) and Neu5,8Ac2 to Neu5Ac and offers a substrate niche. There are multiple prophage-located nanS-homologous open reading frames in the chromosomes of EHEC, that are designated as nanS-p (p = phage) in this study. The question of this thesis was, why EHEC possess multiple nanS-p genes, if their corresponding proteins are used for energy production and for a competition advantage of EHEC. Furthermore, the influence of the sialidase BTSA of Bacteroides thetaiotaomicron on the NanS-p dependent utilization of mucin should be investigated. The strains used in this study were the pathogenic E. coli O157:H7 strain EDL933 as well as the pathogenic O104:H4 strains LB226692 and C227-11phicu (variant of C227-11 cured in its stx-prophage), and the apathogenic E. coli strains AMC 198 (nanS+, nanS-p-) and C600deltananS (nanS-, nanS-p-). The chromosome sequences of EDL933 and LB226692 were analyzed in silico. NanS-p2 and NanS-p4 of EDL933 were expressed recombinantly and the pH- and temperature-optimum as well as potential substrates were investigated. nanS/nanS-p deletion mutants of EDL933 and C227-11phicu were generated and cultivated with Neu5,9Ac2 or mucin. The courses of the growth curves were analyzed by turbidity measurement or determination of the viable cell counts. In co-cultivation experiments the medium was supplemented with the AMC 198 strain and/or BTSA and/or NanS-p. EDL933 possess the chromosomal nanS and seven nanS-p genes, while LB226692 has no nanS, but five nanS-p genes. It was confirmed, that all nanS-p genes are located in the late regulated gene region of the prophages. The putative NanS-p proteins include the domain 303, which is known for its esterase activity in NanS, and the domain of unknown function 1737. The analyzed recombinant NanS-p proteins de-O-acetylated the substrates Neu5,9Ac2 and mucin of bovine submaxillary gland and showed a temperature- and pH-optimum of 40-50 °C and 7-9, respectively. A gene-dose effect was identified because the generation times of the deletion mutant strains increased with the number of deleted nanS-p genes in the chromosomes. After extracellular supplementation with NanS-p, the mutant strains regained the original growth kinetic of the wildtype strain. The mono-deletion of nanS in EDL933 (EDL933deltananS) caused no chances in the growth kinetic of the strain with Neu5,9Ac2. Therefore, NanS is not necessary for growth of EDL933 on Neu5,9Ac2. C600deltananS could not catabolize Neu5,9Ac2, as expected. The original course of the growth curve of a C600 cultivation was recuperated by C600deltananS if NanS-p was added to the medium. In a co-cultivation the viable cell count of C227-11phicu increased, while AMC 198 increased hardly. Only after deletion of all nanS-p genes in C227-11phicu, the viable cell count of AMC 198 increased. In a mucin-containing medium with BTSA as supplement EDL933 and EDL933deltananS could grow in contrast to EDL933deltananSdeltananS-p1a-p7. This shows, that the combination of BTSA and NanS-p supports the growth of EDL933 in a mucin-containing environment. The results of this work showed for the first time the importance of prophage-encoded O-acetyl esterases for EHEC bacteria and are an excellent basis for further work that contribute to a profound scientific understanding of the sialic acid catabolism in EHEC and other pathogenic E. coli. They identify sialic acids as substrates of a potential nutrient niche in the gut and establish a potential location for therapeutic approaches.