Vibrio cholerae is the causal organism of the diarrheal disease cholera. The rugose variant of V. cholerae is associated with the secretion of an exopolysaccharide. The rugose polysaccharide has been shown to confer increased resistance to a variety of agents, such as chlorine, bioacids, and oxidative and osmotic stresses. It also promotes biofilm formation, thereby increasing the survival of the bacteria in the aquatic environments. Here we show that the extracellular protein secretion system (gene designated eps) is involved directly or indirectly in the production of rugose polysaccharide. A TnphoA insertion in epsD gene of the eps operon abolished the production of rugose polysaccharide, reduced the secretion of cholera toxin and hemolysin, and resulted in a nonmotile phenotype. We have constructed defined mutations of the epsD and epsE genes that affected these phenotypes and complemented these defects by plasmid clones of the respective wild-type genes. These results suggest a major role for the eps system in pathogenesis and environmental survival of V. cholerae.Vibrio cholerae is a gram-negative bacterium that causes the diarrheal disease cholera, which continues to be a global threat. Seven pandemics have been recorded in the history of cholera, and a novel epidemic strain, O139 Bengal, has emerged recently (15). In countries where cholera is endemic, such as Bangladesh and India, cholera occurs in seasonal peaks intermittent with an endemicity baseline (8). The survival of V. cholerae during interepidemic periods has long been a key question. It has been proposed that V. cholerae can enter into a nonculturable state but remain viable and capable of producing disease (35,42). It has also been shown that V. cholerae cells remain associated with plankton, which may be reservoirs of this bacterium (13).V. cholerae can switch to another survival form, known as the rugose phenotype, while retaining virulence (28,34,49). The rugose phenotype, as originally described by Bruce White in 1938, is characterized by wrinkled colony morphology associated with the secretion of copious amounts of extracellular polysaccharide (49,50). Under normal growth conditions, the shift from smooth to rugose or vice versa occurs at a low frequency that can be increased by growth in alkaline peptone water for 2 to 3 days at 37°C (28) or by starvation in M9 salts at 16°C (45, 46). V. cholerae serogroup O1 El Tor, serogroup O139, and non-O1 strains have been shown to switch to the rugose phenotype, although O1 classical strains have not (28,52).The rugose form of V. cholerae exhibits increased resistance to chlorine, acid, serum killing, and oxidative and osmotic shocks (28, 34, 45, E.

The authors utilized a recently developed DNA probe technique to obtain quantitative data on occurrence of Vibrio cholerae in samples collected monthly from 12 environmental sites in Lima, Peru, from November 1993 through March 1995. Peak V. cholerae counts ranged from 10(2)/ml to 10(5)/ml, with the highest counts in sewage-contaminated areas and irrigation water. With our methodology, no V. cholerae cases were detected at any site during the winter months of July through October. Counts were detectable in the environment before onset of cholera in the community, with counts at "cleaner" sites upriver correlating significantly with occurrence of community disease 2 and 3 months later. In sites with heavy sewage contamination, V. cholerae could still be detected before the onset of cases in the community; however, in contrast to upriver sites, counts at these latter sites correlated most closely with the number of concurrently occurring cholera cases. These data support a model of cholera seasonality in which initial increases in number of V. cholerae in the environment (possibly triggered by temperature) are followed by onset of illness in the community, with these human cases further amplifying the organism as the epidemic cycle proceeds.

This study aimed to evaluate under field conditions the efficiency in the use ofN coated with urease inhibitor in maize. The experiment was conducted in the year of 2007/2008. The experimental design was a randomized block design in a factorial 2 x 6, with five repetitions, constituted the N sources (common and coated with urease inhibitor) and levels (0, 40, 80, 120, 160 and 200 kg ha-1 of N) sidedressing nitrogen application in the growth stage V4. Based on the data obtained were determined recovery efficiencies, utilization, agronomic and physiological N applied. In all cases, the efficiency levels for maize were influenced by levels of sidedressing nitrogen application, in which increasing levels of N resulted in a decrease of the efficiencies, regardless of the source being common urea or coated with urease inhibitor.