Survival of Escherichia coli in the environment: fundamental and public health aspects

In this review, our current understanding of the species Escherichia coli and its persistence in the open environment is examined. E. coli consists of six different subgroups, which are separable by genomic analyses. Strains within each subgroup occupy various ecological niches, and can be broadly characterized by either commensalistic or different pathogenic behaviour. In relevant cases, genomic islands can be pinpointed that underpin the behaviour. Thus, genomic islands of, on the one hand, broad environmental significance, and, on the other hand, virulence, are highlighted in the context of E. coli survival in its niches. A focus is further placed on experimental studies on the survival of the different types of E. coli in soil, manure and water. Overall, the data suggest that E. coli can persist, for varying periods of time, in such terrestrial and aquatic habitats. In particular, the considerable persistence of the pathogenic E. coli O157:H7 is of importance, as its acid tolerance may be expected to confer a fitness asset in the more acidic environments. In this context, the extent to which E. coli interacts with its human/animal host and the organism''s survivability in natural environments are compared. In addition, the effect of the diversity and community structure of the indigenous microbiota on the fate of invading E. coli populations in the open environment is discussed. Such a relationship is of importance to our knowledge of both public and environmental health.     

Characterization of chlorobenzoate degraders isolated from polychlorinated biphenyl-contaminated soil and sediment in the Czech Republic

Two polychlorinated biphenyl-contaminated sites in the Czech Republic, a soil at Zamberk and a sediment sludge at Milevsko, were screened for the presence of chlorobenzoate degraders. Sixteen different chlorobenzoate degraders were isolated from the soil compared with only three strains isolated from the sediment. From these strains, only four soil degraders and one strain isolated from the sediment, respectively, were shown to possess a complete chlorobenzoate (CB) pathway. Bacteria isolated from the soil have expressed more flexibility for CB degradation, namely in the case of ortho-chlorinated benzoates. They all possessed large plasmids, the restriction patterns of which were compared. Plasmids in Pseudomonas sp. A7, A8, A18 and A19, respectively, were cured and found to encode at least part of the metabolic pathway involved in the growth on ortho-chlorinated benzoates.     

Preferential expression of cellular retinoic acid binding protein in a subpopulation of neural cells in the developing mouse embryo

The cellular retinoic acid binding protein is thought to be involved in the retinoic-acid-mediated signal transduction pathway. We have isolated the mouse cellular retinoic acid binding protein cDNA from an embryonal-carcinoma-derived cell line by using differential cDNA cloning strategies. In situ hybridization on sections of mouse embryos of various developmental stages indicated that the cellular retinoic acid binding protein gene, which we localized on mouse chromosome 9, is preferentially expressed in a subpopulation of neurectodermal cells. This restricted expression pattern suggests an important role for cellular retinoic acid binding protein in murine neurogenesis.     

Effect of gibberellic acid on pod set in soybean

Field-grown soybean plants (Glycine max (L.) Merr. cv. Evans) were treated with gibberellic acid (GA₃; 10gl^–1) and/or (2-chloroethyl)-trimethylammonium chloride (CCC; 0.8gl^–1) in 1983 and 1984, and subsequent anthesis, pod set, seed size, seed number, and seed yield were determined at one node. The treatments were applied to five leaves in the center of each plant (typically leaves 7–11) and reproductive development at the node in the center of those leaves was monitored. Gibberellin A₃ applied Early (about 3d before anthesis of the first flower at the monitored node) had no effect on the number of flowers produced, but decreased the fraction of flowers that set pods in both experimental years (by 32% in 1983 and 76% in 1984). Seed size was slightly decreased by the GA₃ treatment in 1983 but not in 1984. The Middle GA₃ treatment (applied about 3 days after the Early treatment) slightly decreased the number of pods set; and Late treatments (9 days after) had no effect. None of the monitored parameters were affected by CCC.The Early experiments were repeated with two additional genotypes, Lincoln and T210. Genotype T210 is a single-gene, dwarf mutant of Lincoln whose stem elongation and leaf expansion are insensitive to GA₃. Gibberellin A₃ affected the reproductive parameters in Lincoln very similarly to Evans but those in T210 were unaffected. This indicates that GA₃ exerts its effect by increasing the mass of vegetative tissue and thus diverting assimilates away from the pods. However, since the mutation in T210 might affect a receptor that is in flowers as well as shoots, it is possible that GA₃ exerted its effect on the normal genotypes directly on the developing pods, rather than indirectly by diverting photoassimilates.