Phylogenetic and functional diversity of the cultivable bacterial community associated with the paralytic shellfish poisoning dinoflagellate Gymnodinium catenatum

摘要

Gymnodinium catenatum is one of several dinoflagellates that produce a suite of neurotoxins called the paralytic shellfish toxins (PST),\udresponsible for outbreaks of paralytic shellfish poisoning in temperate and tropical waters. Previous research suggested that the bacteria\udassociated with the surface of the sexual resting stages (cyst) were important to the production of PST by G. catenatum. This study sought\udto characterise the cultivable bacterial diversity of seven different strains of G. catenatum that produce both high and abnormally low\udamounts of PST, with the long-term aim of understanding the role the bacterial flora has in bloom development and toxicity of this alga.\udSixty-one bacterial isolates were cultured and phylogenetically identified as belonging to the Proteobacteria (70%), Bacteroidetes (26%) or\udActinobacteria (3%). The Alphaproteobacteria were the most numerous both in terms of the number of isolates cultured (49%) and were\udalso the most abundant type of bacteria in each G. catenatum culture. Two phenotypic (functional) traits inferred from the phylogenetic\uddata were shown to be a common feature of the bacteria present in each G. catenatum culture: firstly, Alphaproteobacteria capable of\udaerobic anoxygenic photosynthesis, and secondly, Gammaproteobacteria capable of hydrocarbon utilisation and oligotrophic growth. In\udrelation to reports of autonomous production of PST by dinoflagellate-associated bacteria, PST production by bacterial isolates was\udinvestigated, but none were shown to produce any PST-like toxins. Overall, this study has identified a number of emergent trends in the\udbacterial community of G. catenatum which are mirrored in the bacterial flora of other dinoflagellates, and that are likely to be of especial\udrelevance to the population dynamics of natural and harmful algal blooms.