Vibrio nigripulchritudo monitoring and strain dynamics in shrimp pond sediments.

AIMS: A description of bacterial pathogens in shrimp ponds is necessary to understand their pathogenesis. Vibrio nigripulchritudo was shown to contain saprophytic and pathogenic strains among New Caledonian isolates. We established a method to map the development of V. nigripulchritudo in pond sediments at three different genetic levels: the species level, then at the pathogenic cluster level and finally at the plasmid level, present only in all highly pathogenic isolates. METHODS AND RESULTS: PCR methods were applied to shrimp pond sediments both before and after a mortality outbreak. Using crude samples, the species V. nigripulchritudo is not detected at first (0/42 samples at day 56 post stocking) but appears frequently in the sediments after the mortality event (30/42 at day 107). The distribution of strains from the pathogenic cluster of V. nigripulchritudo also follows this pattern. In contrast, the pSFn1 virulence-associated plasmid was detected in one sample at day 56 and none at day 107. An enrichment method was developed to lower the detection limits of our assays. After enrichment, the species V. nigripulchritudo was detected in all samples at both dates. The number of samples positive for pSFn1 was 42/42 samples at day 56 and 29/42 at day 107. CONCLUSIONS: These results show that the sediments contain V. nigripulchritudo, notably pathogenic strains. Surprisingly, the virulence-associated plasmid pSFn1 found in all V. nigripulchritudo isolated from moribund shrimp appears less frequently in sediments, possibly being useless or even detrimental to its recipient bacteria in this environment. SIGNIFICANCE AND IMPACT OF THE STUDY: This study confirms the presence of pathogenic V. nigripulchritudo strains in shrimp pond sediment before a mortality outbreak complying with a previous hypothesis that sediments could be the infecting reservoir. After the outbreak, both total V. nigripulchritudo and pathogenic strains populations have largely increased, possibly contributing to the recurrent mortality observed in this shrimp vibriosis.

Direct polymerase chain reaction detection of ropy Pediococcus damnosus strains in wine.

AIMS: Glucan-producing strains of Pediococcus damnosus are considered as spoilage micro-organisms because synthesis of glucan leads to an unacceptable viscosity of wine. In this report, we present a polymerase chain reaction (PCR) procedure to detect the presence of such strains in wines. METHODS AND RESULTS: We developed a direct DNA isolation method from the wine microflora using polyvinylpyrrolidone in order to decrease the polyphenolic concentration. The sequence of the plasmid involved in glucan production allowed the design of a primer pair usable for a specific and sensitive PCR procedure, leading to the amplification of a 563-bp fragment. CONCLUSION: The detection limit in wine was 102 cfu ml-1. The detection sensitivity could be increased by using a second primer pair in nested PCR assays. SIGNIFICANCE AND IMPACT OF THE STUDY: The method proved to be efficient for the early and sensitive detection of ropy Ped. damnosus strains during wine-making. Time-consuming culture and colony isolation steps are no longer needed.

Regulating the activity of a cardioacceleratory peptide.

We measured the effect of crustacean cardioactive peptide on Drosophila heart rate in the animal and in a tissue preparation. Crustacean cardioactive peptide increased in vivo basal heart rate 1%, 6%, and 19% and increased in vitro basal heart rate 52%, 25%, and 35% in larvae, pupae, and adults, respectively. In the tissue preparation, the acceleratory period was followed by decreased in vitro heart rates of 42%, 16%, and 13% in larvae, pupae, and adults, respectively. The effects observed in the animal and tissue and in larvae, pupae, and adults suggest that Drosophila crustacean cardioactive peptide cardiac signaling is modulated and developmentally regulated.

Actin assembly activity of cytochalasins and cytochalasin analogs assayed using fluorescence photobleaching recovery.

The effects on actin self-assembly of 9 common cytochalasins and 9 synthetic analogs have been assayed using fluorescence photobleaching recovery (FPR). The specific assembly activities of cytochalasins determined by this assay are (i) reduction of the fraction of actin molecules incorporated into filaments; (ii) increase of the steady-state diffusion coefficients of filaments, from which filaments shortening may be inferred; and (iii) acceleration of the initial rate of assembly. Of the compounds studied, only cytochalasin D shows strong activity of all three types. The range of activities shown by other compounds indicates clearly that these three activity types are distinct and independent. Inspection of the molecular structures of these 18 compounds for correlation of structure and activity reveals that the three different activities depend on distinct structural features. The Mg2+ dependence of filament-shortening activity by certain cytochalasins may be explained by the Mg2+ chelating ability of two suitably positioned oxygen atoms on the convex face of the bicyclic isoindolone system. Inhibition of filament elongation may involve very specific, high-affinity cytochalasin interactions at a binding site on terminal actin molecules, while accelerating activity may occur by weaker, less specific binding interactions of cytochalasins with monomeric actin.