Algae and Bacteria, a toxic relationship

Gymnodinium catenatum is a species of dinoflagellate which, like many other dinoflagellates, produces paralytic shellfish toxins (PST), a range of compounds responsible for paralytic shellfish poisoning. Many in depth studies on PST-producing dinoflagellates have been carried out over the years, and have revealed that these algae live in association with complex bacterial communities, which have a large effect on the cellular toxicity of the algae.

Using G. catenatum, and a bacterial community replacement method, Albinsson et al. (2014) studied how changing the associated bacterial community composition affected the toxicity, and how large the effect would be.  

Previous studies of the ‘normal’ bacterial community associated with G. catenatum have been carried out, finding that the algae-bacteria association is obligate for the algae, and shown that Alcanivorax and Marinobacter are constant and dominant in these cultures. Not only that, but both Alcanivorax and Marinobacter are capable of maintaining and supporting G. catenatum cells alone. Therefore, building on this information, Albinsson et al., took lab-grown offspring cultures of G. catenatum and grew them in the presence of various bacterial community compositions to then measure the range and amount of PST produced.

The method of offspring production (a sexual cross method), and the interest in the role of Alcanivorax and Marinobacter determined the different bacterial communities tested on the algae in this experiment. Sterile offspring were grown in the presence of Alcanivorax only, Marinobacter only, the communities associated with each of the algal parent strains, and 2 controls, one being completely sterile and another being the combined parental communities.

As expected, the algal cells grown in the sterile control did not survive, as stated earlier, they have an obligate relationship with their bacterial community. Additionally, there were no significant changes in the types of PST produced by the offspring cultures, only changes in the levels of net PST production. Interestingly, this study showed that there was significantly lower toxin content in the cultures grown in the presence of Alcanivorax or Marinobacter than in the cultures grown with mixed bacterial communities. Additionally, although non-significant, the net toxin production rates in offspring cultures were almost 8-fold lower than that of the parents, which indicates that lab conditions are likely having some effect on the results.

Though there are multiple reasons for the changes in toxicity of an algal cell relating to its bacterial community, such as the actual bacteria present, a reduction in community complexity or a combination of both, these findings lean more towards a reduction in bacterial complexity being the reason behind the reduction in toxicity.

The results from this work, combined with other studies showing that Marinobacter doesn’t produce PST toxins suggests that it is likely that the interactions between the bacteria themselves, and between the bacteria and the algae have more influence over the toxicity of the algae, rather than the individual activities of bacteria.

I feel that this paper contributes some interesting findings to the field of bacterial associations and interactions, and emphasises the need for further studies on how bacterial interactions (with other bacteria and other organisms) play an important role in not only toxin production, but pathogenicity, diseases and other behaviours.

http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0104623 

M. E. Albinsson, A. P. (2014). Bacterial Community Affects Toxin Production by Gymnodinium catenatum. PLoS One.