A Clonal Shiga Toxin-Producing Escherichia coli O121:H19 Population Exhibits Diverse Carbon Utilization Patterns.

Shiga toxin-producing Escherichia coli (STEC) serotype O121:H19 is one of the major non-O157:H7 serotypes associated with severe human disease. Here we examined population structure, virulence potential, and metabolic profile of environmental STEC O121 strains recovered from a major produce production region in California and performed comparative analyses with STEC O121 clinical isolates. Multilocus sequence typing revealed that sequence type (ST)-655, a common ST in clinical strains, was the predominant genotype among the environmental strains. Phylotyping placed all STEC O121 strains in B1 group, a lineage containing other major non-O157 serogroups of STEC. Genes encoding different subtypes of Shiga toxin 1 and 2 were detected in O121, including stx1a, stx1d, stx2a, and stx2e. Furthermore, genes encoding intimin (eae) and enterohemolysin (ehxA) were detected in a majority of environmental strains (83.3%), suggesting that the majority of environmental STEC O121 strains are enterohemorrhagic E. coli. The STEC O121 strains with the same genotype were clustered together based on the carbon utilization pattern. Among the 122 carbon substrates that supported the growth of STEC O121 strains, 44 and 35 exhibited lineage (ST) and strain-specific metabolic profiles, respectively. Although clinical ST-655 strains displayed higher metabolic activity than environmental ST-655 strains for several carbon substrates, including l-alaninamide, 5-keto-d-gluconic acid, 3-O-ß-d-galactopyranosyl-d-arabinose, α-ketoglutaric acid, and lactulose, a few environmental strains with the enhanced metabolic potential for the above substrates were detected. Variations in curli biogenesis and swimming motility were also observed in ST-655 strains, suggesting that phenotypic variants are widespread in STEC. Considering the ecological niches that STEC colonizes, increased metabolic potential for plant-derived carbohydrates, mucus-derived substrates, or secondary metabolites produced by the indigenous microorganisms might have been selected. Such traits would confer STEC competitive advantages and facilitate survival and adaptation of STEC population to a given niche, including infected humans.

[Study on ion beam mutagenizing of the Trichosporon lactis T for enantioselective separation of ibuprofen].

The initial strain, Trichosporon Lactis T, isolated from soil sample, having the capability of enantioselectively hydrolyzing S-isomer of racemic ibuprofen ethyl-ester into the corresponding S-ibuprofen, was implanted by 30 KeV, 1 x 10(15) ions/cm2 - 5 x 10(15) ions/cm2 low-energy N+ for the purpose of obtaining mutants with high-efficiency hydrolyzing enzyme to produce active S-ibuprofen. Under the dosage of 30 KeV, 4 x 10(15) ions/cm2, the mutation rate is the highest, with 32.9 % positive and 37.1% negative mutant, respectively. Therefore, 30 KeV, 4 x 10(15) ions/cm2 is chosen as the optimal implantation dosage. Under optimal implantation dosage, seven mutants with high-efficiency hydrolyzing enzyme are selected after N+ implantation. The genetic stability test shows that T. lactis K1, one of the seven mutants, has a stable hydrolyzing ability during consecutive five-generation. The enzyme activity of T. lactis K1 is higher with 50% than that of the initial strain after 24 h cultivation, and the highest enzyme activity of T. lactis K1 appears 6h earlier than that of the initial strain. After 24 h cultivation and succeeding 24 h incubation with ibuprofen ethyl ester, the S-ibuprofen production of T. lactis K1 is 6.96 g/L, 64.2% higher than that of T. lactis T, which only produces 4.24 g/L S-ibuprofen at the same time, the specific rotation and enantiomeric excess (ee%) of the S-ibuprofen produced by two stains, however, are the same, + 54.1 degrees and 98%, respectively.