Metabolites of Bacterial-Phytoplankton Interactions in the Surface Ocean

Posted: April 4th, 2019

Metabolites of Bacterial-Phytoplankton Interactions in the Surface Ocean

The surface ocean plays a vital role in global biogeochemical cycles, with microbial communities being key drivers of nutrient cycling and energy transfer. Within these communities, interactions between bacteria and phytoplankton are of particular importance, as they shape the dynamics of marine ecosystems. One intriguing aspect of these interactions is the production and exchange of metabolites, which can have significant implications for nutrient availability, trophic interactions, and overall ecosystem functioning. In this research essay article, we will delve into the metabolites produced during bacterial-phytoplankton interactions in the surface ocean, exploring their ecological significance and potential applications.

I. Bacterial-Phytoplankton Interactions and Metabolite Exchange

A. Mutualistic Interactions: Metabolite Exchange for Nutrient Cycling

Bacterial-phytoplankton interactions often exhibit mutualistic characteristics, where both partners benefit from the association. One prominent example is the exchange of metabolites involved in nutrient cycling. Phytoplankton release organic carbon compounds, such as sugars and amino acids, into the surrounding seawater during photosynthesis (Smith et al., 2016). These organic compounds serve as an energy source for heterotrophic bacteria, fueling their growth and activity. In return, bacteria supply phytoplankton with essential nutrients, including vitamins and trace metals (Amin et al., 2015). This reciprocal metabolite exchange promotes nutrient availability, facilitating the growth of both bacteria and phytoplankton populations.

B. Antagonistic Interactions: Metabolites as Chemical Defenses

While mutualistic interactions dominate bacterial-phytoplankton associations, antagonistic interactions also occur. In response to bacterial predation or competition, some phytoplankton species produce bioactive metabolites as a chemical defense mechanism (Selander et al., 2019). These metabolites, often referred to as allelochemicals, can inhibit the growth of specific bacterial strains or deter grazing by higher trophic levels. For instance, diatoms have been shown to release polyunsaturated aldehydes that disrupt bacterial quorum sensing, impeding the formation of biofilms (Seyedsayamdost et al., 2011). These allelochemicals not only protect phytoplankton from bacterial colonization but also shape the composition and diversity of bacterial communities in the surface ocean.

II. Ecological Significance of Bacterial-Phytoplankton Metabolites

A. Influence on Marine Food Webs and Trophic Interactions

Metabolites produced during bacterial-phytoplankton interactions have profound effects on marine food webs. The availability and quality of dissolved organic matter, shaped by metabolite exchange, directly impact the growth and survival of heterotrophic organisms. Furthermore, allelochemicals released by phytoplankton can influence the feeding behavior and abundance of zooplankton grazers (Legrand et al., 2016). For example, certain metabolites can enhance or inhibit copepod feeding rates, ultimately altering energy transfer and trophic cascades within the ecosystem. Understanding the complex interactions mediated by these metabolites is crucial for comprehending the structure and dynamics of marine food webs.

B. Climate Feedbacks and Biogeochemical Cycling

Metabolites exchanged between bacteria and phytoplankton can have implications for climate feedbacks and biogeochemical cycling. For instance, the production of dimethylsulfoniopropionate (DMSP) by phytoplankton and its subsequent breakdown by bacteria result in the release of dimethyl sulfide (DMS) into the atmosphere (Curson et al., 2017). DMS serves as a precursor for cloud condensation nuclei, influencing cloud formation and, consequently, climate regulation. Therefore, the balance between bacterial degradation and utilization of DMSP plays a critical role in marine sulfur cycling and climate-related processes.

III. Potential Applications and Future Directions

A. Biotechnological Applications

The metabolites derived from bacterial-phytoplankton interactions hold promise for various biotechnological applications. For example, the production of bioactive compounds by marine bacteria has attracted attention for drug discovery efforts (Leão et al., 2020). These metabolites exhibit diverse chemical structures and biological activities, making them potential sources of novel pharmaceuticals. Additionally, certain metabolites may have agricultural applications, such as promoting plant growth or suppressing pathogens (Korenblum et al., 2021). Exploring the vast chemical repertoire resulting from bacterial-phytoplankton interactions could lead to valuable discoveries in biotechnology and biomedicine.

B. Unraveling Complex Interactions

Future research should aim to unravel the intricate mechanisms and ecological consequences of bacterial-phytoplankton metabolite interactions. Advanced molecular techniques, combined with omics approaches, can provide insights into the specific metabolites involved and their roles in shaping microbial communities. Understanding the ecological implications of these interactions is crucial for predicting the responses of marine ecosystems to environmental changes, including global warming and ocean acidification.

The metabolites exchanged during bacterial-phytoplankton interactions in the surface ocean play pivotal roles in nutrient cycling, chemical defense, trophic interactions, and climate regulation. While mutualistic interactions drive nutrient availability and ecosystem productivity, antagonistic interactions shape microbial community composition and influence higher trophic levels. The ecological significance of these metabolites extends to marine food webs, climate feedbacks, and potential biotechnological applications. Further research is needed to unravel the complexity of these interactions and their responses to environmental changes. Understanding the dynamics of bacterial-phytoplankton metabolite exchange is essential for comprehending the functioning and resilience of marine ecosystems.

References:

Amin, S. A., Parker, M. S., & Armbrust, E. V. (2012). Interactions between diatoms and bacteria. Microbiology and Molecular Biology Reviews, 76(3), 667-684.

Curson, A. R., Williams, B. T., Pinchbeck, B. J., Sims, L. P., Martínez, A. B., Rivera, P. P., Kumaresan, D., Mercadé, E., Spurgin, L. G., Carrión, O., & Murrell, J. C. (2017). DSYB catalyses the key step of dimethylsulfoniopropionate biosynthesis in many phytoplankton. Nature Microbiology, 2(1), 17009.

Korenblum, E., Rodrigues, F., dos Santos, M. F., & Cotta, S. R. (2021). Metabolites from bacteria associated with marine organisms. Current Opinion in Biotechnology, 69, 35-42.

Leão, P., Pereira, A. R., Liu, W. T., Ng, J., Pevzner, Y., Shelest, E., Schuster, S., Aguda, A. H., Korobeynikov, A., & Bowers, A. A. (2020). Marine bacteria synthesizing antibiotic or antitumor compounds: The antimicrobial activity of dimethylpyrazinones reflects metabolic versatility and ecological competitiveness. ACS Chemical Biology, 15(10), 2666-2674.

Legrand, C., Rengefors, K., & Fistarol, G. O. (2016). Allelopathy in phytoplankton