Complex Relationships between the Blue Pigment Marennine and Marine Bacteria of the Genus Vibrio

Adele James

Abstract:

Marennine, the water-soluble blue pigment produced by the marine diatom Haslea ostrearia,
is known to display antibacterial activities. Previous studies have demonstrated a prophylactic
effect of marennine on bivalve larvae challenged with a pathogenic Vibrio splendidus, suggesting
that the blue Haslea is a good candidate for applications in aquaculture as a source of a natural
antimicrobial agent. Indeed, the genus Vibrio is ubiquitous in aquaculture ecosystems, and regular
events of pathogenic invasion cause some of the biggest losses worldwide. To better characterize
the effects of marennine on Vibrios, a panel of 30 Vibrio strains belonging to 10 different species
was tested, including bivalve pathogenic species (e.g., Vibrio crassostreae and Vibrio harveyi). Vibrio
strains were first exposed to 10 and 25 µg mL−1 of Blue Water (BW), a concentrated culture
supernatant of H. ostrearia containing marennine. This screening evidenced a great diversity in
responses, from growth stimulation to a total inhibition, at both the interspecific or intraspecific level.
In a second series of experiments, 10 Vibrio strains were exposed to BW at concentrations ranging from
5 to 80 µg mL−1
. The highest concentrations of BW did not systematically result in the highest growth
inhibition as hormetic responses—opposite effects regarding the concentration—were occasionally
evidenced. The relationships between marennine and Vibrio strains appear more complex than
expected and justify further study—in particular, on the mechanisms of action—before considering
applications as a natural prophylactic or antibiotic agent in aquaculture.