Bacteriostatic anti-Vibrio parahaemolyticus activity of Pseudoalteromonas sp strains DIT09, DIT44 and DIT46 isolated from Southern Chilean intertidal Perumytilus purpuratus

We characterised the anti- (anti-) marine bacteria DIT09, DIT44 and DIT46 isolated from the intertidal mussel . The 16S rRNA gene sequences identify a sp. that form a clade with and . The strains produced bacteriostatic anti- agents during the exponential growth phase, which were also active against and , but not on other Gram positive and Gram negative bacteria. Bacteriostatic agents could be permeated by analytic ultra-filtration with 3.5 kDa cut-off, partially precipitated with 70 and 90 % ammonium sulphate, but not extracted with ethyl acetate. Reverse-phase HPLC revealed the production of a set of 5-6 active compounds by each strain (elution from 20 to 40 % acetonitrile), with similar but non identical HPLC patterns. Additionally, was able to progressively overcome the inhibition of antibiotics in trypticase soy agar with Fe(III) 0.5 up to 2 mM, suggesting the involvement of a set of novel siderophore or active molecules targeted at different Fe-siderophore uptake systems. The overall findings suggest that sp. DIT strains produce a putatively novel class of bacteriostatic and probably amphiphilic anti- agents, indicating the need for further studies with chemical purification followed by their structural and functional characterization. Finally, the crude cell-free extracts, as well as the strains incubated at 10(3) and 10(5) c.f.u./mL, did not cause mortality in nauplii, suggesting that these bacteria are serious candidates for further probiotic evaluations with shellfish and fish cultures.