Transcription of redD, the activator gene required for production of the red-pigmented antibiotic undecylprodigiosin by Streptomyces coelicolor A3(2), showed a dramatic increase during the transition from exponential to stationary phase. The increase in redD expression was followed by transcription of redX, a biosynthetic structural gene, and the appearance of the antibiotic in the mycelium, and coincided with the intracellular appearance of ppGpp. However, ppGpp production elicited either by nutritional shift-down of, or addition of serine hydroxamate to, exponentially growing cultures had no stimulatory effect on redD transcription. The presence of redD on a multicopy plasmid resulted in elevated levels of the redD transcript and production of redX and undecylprodigiosin during exponential growth; the normal growth-phase-dependent production of undecylprodigiosin appeared to be mediated entirely through the redD promoter, which shows limited similarity to the consensus sequence for the major class of eubacterial promoters.

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The stringent response was elicited in the antibiotic producer Streptomyces coelicolor A3(2) either by amino acid depletion (nutritional shiftdown) or by the addition of serine hydroxamate; both led to increased levels of ppGpp and to a reduction in transcription from the four promoters of the rrnD rRNA gene set. Analysis of untreated batch cultures revealed elevated ppGpp levels at the end of exponential growth, preceding the onset of antibiotic production. The effect of provoking the stringent response on antibiotic production in exponentially growing cultures was assessed by S1 nuclease mapping of actIII, an early gene of the actinorhodin biosynthetic cluster. Expression of actIII occurred after nutritional shiftdown, but not after treatment with serine hydroxamate. Although the need for ppGpp in triggering antibiotic production remains equivocal, ppGpp synthesis alone does not appear to be sufficient to initiate secondary metabolism in S. coelicolor A3(2).

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Global change has caused a worldwide increase in reports of Vibrio-associated diseases with ecosystem-wide impacts on humans and marine animals. In Europe, higher prevalence of human infections followed regional climatic trends with outbreaks occurring during episodes of unusually warm weather. Similar patterns were also observed in Vibrio-associated diseases affecting marine organisms such as fish, bivalves and corals. Basic knowledge is still lacking on the ecology and evolutionary biology of these bacteria as well as on their virulence mechanisms. Current limitations in experimental systems to study infection and the lack of diagnostic tools still prevent a better understanding of Vibrio emergence. A major challenge is to foster cooperation between fundamental and applied research in order to investigate the consequences of pathogen emergence in natural Vibrio populations and answer federative questions that meet societal needs. Here we report the proceedings of the first European workshop dedicated to these specific goals of the Vibrio research community by connecting current knowledge to societal issues related to ocean health and food security.

Shiga toxin 2e (Stx2e)-producing strains from food (n ‫؍‬ 36), slaughtered pigs (n ‫؍‬ 25), the environment (n ‫؍‬ 21), diseased pigs (n ‫؍‬ 19), and humans (n ‫؍‬ 9) were investigated for production of Stx2e by enzymelinked immunosorbent assay, for virulence markers by PCR, and for their serotypes to evaluate their role as potential human pathogens. Stx2e production was low in 64% of all 110 strains. Stx2e production was inducible by mitomycin C but differed considerably between strains. Analysis by nucleotide sequencing and transcription of stx 2e genes in high-and low-Stx2e-producing strains showed that toxin production correlated with transcription rates of stx 2e genes. DNA sequences specific for the int, Q, dam, and S genes of the stx 2e bacteriophage P27 were found in 109 strains, indicating cryptic P27-like prophages, although 102 of these were not complete for all genes tested. Genes encoding intimin (eae), enterohemorrhagic Escherichia coli hemolysin (ehx), or other stx 1 or stx 2 variants were not found, whereas genes for heat-stable enterotoxins STI, STII, or EAST1 were present in 54.5% of the strains. Seven major serotypes that were associated with diseased pigs (O138:H14, O139:H1, and O141:H4) or with slaughter pigs, food, and the environment (O8:H4, O8:H9, O100:H30, and O101:H9) accounted for 60% of all Stx2e strains. The human Stx2e isolates did not belong to these major serotypes of Stx2e strains, and high production of Stx2e in human strains was not related to diarrheal disease. The results from this study and other studies do not point to Stx2e as a pathogenicity factor for diarrhea and hemolytic uremic syndrome in humans.

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