Phycosphere fad

The phycosphere is the region around the outside of cells which is rich in organic matter and surrounds an algal cell. This area is a small niche in which bacterial communities have been shown to inhabit, utilise the extracellular products and show chemotaxis towards. Some bacteria have been shown to cause lysis or inhibit growth of harmful algal bloom (HAB) species. This is a dynamic interaction affected by different environments. Yang et al (2013) looked at the effect of algicidal bacteria on two species of red tide causing algae, Skeletonema costatum and Scrippsiella trochoidea. They looked to build upon research by Zhang et al (2010) and aimed to visualise algal morphology under SEM as well as characterising the use of different carbon forms by the communities.

When a medium that favoured bacterial growth was added the algae lysed within 72 hours, demonstrating a finite balance between the algae and its phycosphere occupiers. The morphology of the two species was similar after 48 hours, with the cells being severely deformed. S. costatum differed in bacteria being attached to the algal surface, unlike S. trochoidea. The bacterial community of S. trochoidea utilised were more diverse than S. costatum, reflecting the dynamic change in the community. The phycosphere microbial diversity indices were significantly lower than those of natural environments, suggesting a potentially more simple community structure within the phycosphere. During the lysis period, the density of bacterial cells dramatically increased, demonstrating that a large number of cells is require to induce lysis.

Biolog ECO microplates were used to assess the community level physiology of the two red tide causing species. S. trochoidea bacterial community also differed by utilising carbon more quickly than S. costatum. Both species’ sources of carbon varied significantly during the lysis of the algae and the main sources (polymers, carboxylic acids, amino acids and carbohydrates) were similar, but Skeletonema costatum carbon source use is more complex. There was an increase in the use of carboxylic acids and amino acids which may indicate the production of extracellular enzymes. These may be used to take up nutrients and causing lysis.  

Overall, I like this paper, I think it is an exciting area of research and one I had not previously considered prior to reading about in a review by Worden et al (2015). Although I feel their discussion leaves a bit to be desired and is a little messy, by not following the same clear structure given throughout the rest of the paper.  I do find myself wondering what the algicide bacteria is, therefore I think it would be interesting to use 16s rRNA sequencing to identify what the dominant species is during the lysis phase. It would also be useful for authors to further study the phycosphere in relation to biogeochemical cycles, such as carbon.

Reviewed paper:

Yang, Y., Hu, X., Zhang, J., & Gong, Y. (2013). Community level physiological study of algicidal bacteria in the phycospheres of Skeletonema costatum and Scrippsiella trochoidea. Harmful algae, 28, 88-96.

Worden, A. Z., Follows, M. J., Giovannoni, S. J., Wilken, S., Zimmerman, A. E., & Keeling, P. J. (2015). Rethinking the marine carbon cycle: Factoring in the multifarious lifestyles of microbes. Science, 347(6223), 1257594.

Zhang, J., Yang, Y. F., Gong, Y. X., Zhang, J. Y., & Jiang, J. L. (2010). The lytic effect of bacteria in the phycosphere of Skeletonema costatum and Scrippsiella trochoidea. Acta Sci Circumst, 30, 1271-1279.