Responses of marine planktonic protists to amino acids

Signaling among microbes has been studied widely at both individual and community level. For instance the formation of biofilms is a product of community response to signaling molecules (Pasmore and Costerton, 2003). However, the role of signaling in regulating microbial predator-prey interaction is not well studied. As ocean’s primary production is consumed by microbes, microbial predator-prey interaction therefore have a consequence on the biogeochemical cycling in the ocean. 

This paper built on the concept, from past research, that feeding by free-living marine ciliates and heterotrophic dinoflagellates is inhibited by the organic osmolyte dimethylsulfoniopropionate (DMSP) (Strom et al., 2003). Structural analogues of DMSP have also shown to reduce feeding in dinoflagellate Amphidinium longum. These includes glycine, betaine and N,N-dimethyl glycine. These results were controversial to prior work on organisms from bacteria to fish has shown positive responses to amino acids (Poulet & Ouellet 1982, Levandowsky et al.1984, Valentincic 1985, Miller et al. 2004).

Dissolve free amino acids (DFAAs) acts as chemical cues and signaling function that affects the feeding and swimming behavior of planktonic ciliate Favella species.This paper explore the effects of a range of compounds, especially amino acids and DMSP, on feeding responses and swimming behavior of protists and dinoflagellate. The research focus on Favella sp., a genus of relatively large ciliates widely distributed in coastal seas (Pierce and Turner 1993), also studies on aloricate spirotrich ciliate and a heterotrophic dinoflagellate. They show that amino acids and the structurally related compounds betaine and DMSP inhibited feeding in the ciliates, but not in the dinoflagellate.

The authors have also shown that of the range of inhibitory amino acids tested on ciliates, they saw a correlation of the strength of inhibition was inversely proportional to the length of the amino acid side chain. In terms of chronic effects, longer exposure to amino acids led to partial adaptation but not complete recovery. However this does not hold true in the presence of serine amino acid. Moreover, partial recovery was immediate with removal of inhibitory amino acids. Lastly, swimming behavior did not shown dramatic changes in the experiment carried out.  

The properties of Favella sp. Signaling response shed light on its possible adaptive significance. This suggest a specific interaction between the cell surface receptors and DFAAs. DFAAs are released both by phytoplankton (prey for Favella sp.) and during grazing by copepods and other zooplankton (potential predators of Favella sp.). The release of theses inhibitory molecules might have an evolutionary effect on the co-existence of the microbes in the ocean.

Strom, S. L., Wolfe, G. V., Bright, K. J. (2007). Responses of marine planktonic protists to amino acids: feeding inhibition and swimming behavior in the ciliate Favella sp. Aquat Microb Ecol. 47: 107-121.