Effects of ecological factors on the survival and physiology of Ralstonia solanacearum biovar 2 in agricultural drainage water

J.D. van Elsas, P. Kastelein, P.M. de Vries, L.S. van Overbeek

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    Abstract

    The fate of Ralstonia solanacearum bv. 2, the causative agent of brown rot in potato, in aquatic habitats of temperate climate regions is still poorly understood. In this study, the population dynamics and the physiological response of R. solanacearum bv. 2 were tested in sterile pure water and in agricultural drainage water obtained from waterways near potato cropping fields in the Netherlands. The behaviour of five different biovar 2 isolates in drainage water at 20C was very similar among strains. One typical isolate with consistent virulence (strain 1609) was selected for further studies. The effects of temperature, light, canal sediment, seawater salts, and the presence of competing microorganisms on the survival of strain 1609 were assessed. Moreover, the impacts of the physiological state of the inoculum and the inoculum density were analyzed. The population dynamics of strain 1609 in sterile pure water were also characterized. In sterile pure water, the fate of R. solanacearum 1609 cells depended strongly on temperature, irrespective of inoculum density or physiological state. At 4C and 44C, strain 1609 CFU numbers showed declines, whereas the strain was able to undergo several cell divisions at 12C, 20C, and 28C. At 20C and 28C, repeated growth took place when the organism was serially transferred, at low inoculum density, from grown water cultures into fresh water devoid of nutrients. Both at low and high cell densities and regardless of physiological state, R. solanacearum 1609 cells persisted as culturable cells for limited periods of time in drainage water. A major effect of temperature was found, with survival being maximal at 12C, 20C, and 28C. Temperatures of 4C, 36C, or 44C induced accelerated declines of the culturable cell numbers. The drainage water biota had a strong effect on survival at 12C, 20C, and 28C, as the persistence of strain 1609 was significantly enhanced in sterile drainage water systems. Furthermore, there was a negative effect of incident light, in a light:dark regime, on the survival of R. solanacearum 1609 in natural drainage water. Also, levels of seawater salts realistic for drainage water in coastal areas were detrimental to strain survival. Ralstonia solanacearum 1609 showed considerable persistence in canal sediment saturated with drainage water, but died out quickly when this sediment was subjected to drying. Evidence was obtained for the conversion of R. solanacearum 1609 cells to nonculturable cells in water microcosms kept at 4C, but not in those kept at 20oC. A substantial fraction of the cells found to be nonculturable were still viable, as evidenced by the direct viable count and by staining with the redox dye 5-cyano-2,3-ditolyl tetrazolium chloride. The potential occurrence of viable-but-nonculturable cells in natural waters poses a problem for the detection of R. solanacearum by cultivation-based methods.Key words: survival, Ralstonia solanacearum, irrigation water, ecological factors
    Original languageEnglish
    Pages (from-to)842-854
    JournalCanadian Journal of Microbiology
    Volume47
    Issue number9
    DOIs
    Publication statusPublished - 2001

    Keywords

    • pseudomonas-solanacearum
    • soil
    • immunofluorescence
    • flavobacterium
    • climates
    • bacteria

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