Stock, F., De Decker, S., Osuna-Cruz, C.-M., Van den Berge, K., VancaesterE., De Veylder, L., Vandepoele, K., Mangelinckx, S., and Vyverman, W. (2020). Frontiers in Microbiology. 

Distinctive growth and transcriptional changes in the diatom Seminavis robusta in response to quorum sensing related compounds

Diatoms are often closely associated with marine bacteria which use N-acyl homoserine lactones (AHLs) as signaling molecules. This signaling process is also known as  quorum sensing. It has been suggested that diatoms could distinguish between beneficial and detrimental bacteria in their surroundings by sensing AHLs. We know that some microalgae can interfere with AHL signaling, for example by releasing AHL mimics or degrading AHLs. However, it is still unclear if microalgae can respond to AHLs on a molecular level. To address this question, we tested growth and transcriptional responses of the diatom Seminavis robusta to a selection of quorum sensing compounds. 

In this study, we used three short-chained (C6-HSL, OH-C6-HSL, oxo-C6-HSL) and three long-chained AHLs (C14-HSL, OH-C14-HSL, and oxo-C14-HSL). While none of the tested short-chained AHLs affected growth of S. robusta, long-chained AHLs promoted (C14-HSL) or inhibited (OH-C14-HSL and oxo-C14-HSL) growth. Following this observation, we investigated the physiological effects of long-chained AHLs in more detail by performing a transcriptomics experiment. During this experiment we treated S. robusta with the growth-promoting C14-HSL and the growth-inhibiting oxo-C14-HSL. In addition, we included a tetramic acid (TA14), a structural rearrangement product of oxo-C14-HSL, which also inhibited diatom growth. 

After 3 days of treatment, 3,410 genes were differentially expressed in response to at least one of the tested compounds. In the treatment with the growth-promoting C14-HSL many genes involved in intracellular signaling were upregulated. Exposure to growth-inhibiting oxo-C14-HSL and TA14 on the other hand triggered a switch in lipid metabolism towards increased fatty acid degradation. Furthermore, oxo-C14-HSL led to downregulation of cell cycle genes, which is in agreement with the stagnation of cell growth in this treatment. Combined, our results indicate that bacterial signaling molecules with high structural similarity induce contrasting physiological responses in S. robusta. [Full article]