Metabolomics and proteomics reveal impacts of chemically mediated competition on marine plankton

Abstract

Competition is a major force structuring marine planktonic communities. The release of compounds that inhibit competitors, a process known as allelopathy, may play a role in the maintenance of large blooms of the red-tide dinoflagellate Karenia brevis, which produces potent neurotoxins that negatively impact coastal marine ecosystems. K. brevis is variably allelopathic to multiple competitors, typically causing sublethal suppression of growth. We used metabolomic and proteomic analyses to investigate the role of chemically mediated ecological interactions between K. brevis and two diatom competitors, Asterionellopsis glacialis and Thalassiosira pseudonana. The impact of K. brevis allelopathy on competitor physiology was reflected in the metabolomes and expressed proteomes of both diatoms, although the diatom that co-occurs with K. brevis blooms (A. glacialis) exhibited more robust metabolism in response to K. brevis. The observed partial resistance of A. glacialis to allelopathy may be a result of its frequent exposure to K. brevis blooms in the Gulf of Mexico. For the more sensitive diatom, T. pseudonana, which may not have had opportunity to evolve resistance to K. brevis, allelopathy disrupted energy metabolism and impeded cellular protection mechanisms including altered cell membrane components, inhibited osmoregulation, and increased oxidative stress. Allelopathic compounds appear to target multiple physiological pathways in sensitive competitors, demonstrating that chemical cues in the plankton have the potential to alter large-scale ecosystem processes including primary production and nutrient cycling.

Keywords: chemical ecology; mass spectrometry; systems biology.

Fig. 1.

Effects of exposure to exudates of live K. brevis on the growth of A. glacialis and T. pseudonana. (A) A. glacialis (red) in vivo and T. pseudonana (blue) in vivo fluorescence (arrow indicates day of harvest for metabolomics and proteomics). The solid lines indicate fluorescence of diatom-only controls, and the dashed lines indicate fluorescence of diatoms exposed to K. brevis. Initial K. brevis (red open circles for A. glacialis experiment; blue open circle for T. pseudonana experiment) concentrations from cultures used to fill dialysis tubes (n = 1), final concentrations from experimental flasks at time of harvest (n = 15). (B) Calculated percentage growth of competitors A. glacialis (red) and T. pseudonana (blue) relative to their own controls after 8 and 6 d exposure to K. brevis, respectively. The dotted line indicates growth equivalent to control. n = 15. P < 0.0001 indicated by asterisk (*), unpaired t test. Error bars represent ±1 SEM.

Fig. 2.

Orthogonal PLS-DA shows effects of K. brevis allelopathy on the metabolomes of competitor diatoms. PLS-DA scores plot of (A) UHPLC/MS metabolic features and (B) ¹H NMR spectral data for T. pseudonana exposed to K. brevis (filled squares) or dilute media control (open squares) with cross-validated accuracies of 87% and 100%, respectively. PLS-DA scores plot of (C) UHPLC/MS metabolic features and (D) ¹H NMR spectral data for A. glacialis exposed to live K. brevis (filled circles) or dilute media controls (open circles) with cross-validated accuracies of 57% and 63%, respectively.

Fig. 3.

Network of cellular pathways, enzymes, and metabolites in the diatom T. pseudonana impacted by exposure to K. brevis allelopathy, derived from NMR and MS metabolomics and proteomics. Pathways and metabolites enhanced by allelopathy are indicated by red arrows and compound names, respectively. The blue arrows and compound names denote pathways and metabolites that were suppressed by allelopathy.