The chemical – microbe network underpins ecosystem structure function relationships and biogeochemical cycling in aquatic systems. The metabolites of this network are organic molecules produced during biochemical reactions within organisms that cross all taxonomic levels in aquatic systems. They are analytically challenging to quantify due to their heterogeneous chemical nature and their dilute concentrations in aquatic systems relative to background organic matter. Nevertheless, metabolites play critical roles in determining the functions of aquatic microbiomes, serving as growth substrates, co-factors and/or infochemical signals within microbial consortia. Despite the central role of the chemical-microbe network in the aquatic carbon cycle, our knowledge of metabolites and their dynamics in various aquatic systems remains poor. This session invites presentations on all aspects of metabolite cycling in aquatic systems in laboratory, field and/or modelling investigations. We seek studies that explore the mechanisms behind production of metabolites by autotrophic and heterotrophic organisms, as well as empirical observations of metabolite consumption and numerical modelling investigations of predicted metabolite production and consumption. We are particularly interested in studies that consider shifts in metabolite dynamics and the resiliency of the chemical-microbe network under changing planetary conditions. Analytical method developments that expand the lexicon of metabolites in aquatic studies are also welcome.
Lead Organizer: Elizabeth Kujawinski, WHOI (ekujawinski@whoi.edu)
Co-organizers:
Mary Ann Moran, University of Georgia (mmoran@uga.edu)
Sonya Dyhrman, Columbia University (sdyhrman@ldeo.columbia.edu)
Presentations
06:30 PM
PARSING THE BIOMOLECULAR BASIS BY WHICH A BACTERIAL SIGNALING MOLECULE INDUCES CELLULAR ARREST AND PROTECTION FROM VIRUS-INDUCED MORTALITY IN EMILIANIA HUXLEYI (4776)
Primary Presenter: Oscar Garrett, Haverford College (ogarrett@haverford.edu)
Interactions between marine phytoplankton, viruses, and bacteria drive biogeochemical cycling, shape marine trophic structures, and impact global climate. These interactions are mediated by excreted small compounds – infochemicals – which can impact microbial physiology and community structure. This work aims to reveal the biomolecular mechanism of one such interaction, in which the bacterial quorum sensing molecule 2-heptyl-4-quinolone (HHQ) produced by the marine bacterium Pseudoalteromonas sp. arrests cell division and confers protection against virus-induced mortality in the globally abundant phytoplankton Emiliania huxleyi. Here, we investigate whether HHQ inhibits an enzyme critical for nucleotide biosynthesis – dihydroorotate dehydrogenase (DHODH) – in E. huxleyi, which may explain many of the physiological and metabolic changes induced in E. huxleyi by HHQ. Preliminary evidence supports inhibition of E. huxleyi DHODH (EhDHODH) by HHQ, with 10 uM HHQ being sufficient to significantly reduce endogenous DHODH activity in E. huxleyi cell lysate. The specifics of HHQ's impact on EhDHODH will be further quantified by precisely assaying activity of pure, recombinant EhDHODH exposed to HHQ, yielding an IC50 and a kinetic profile of the inhibited enzyme. By characterizing the mechanisms by which bacterial signals influence phytoplankton physiology and virus-induced mortality, we enhance our ability to decode the chemical crosstalk of marine microorganisms, thereby strengthening our ability to make predictions about the global ecological processes these microorganisms influence.
06:30 PM
THE MICROBIOME EFFECT ON FATTY ACID PROFILES OF A MARINE DIATOM (5675)
Primary Presenter: Alessandra Kronschnabel, University of Bremen (alekro@uni-bremen.de)
Marine diatoms rely on essential micronutrients, vitamins and many other mostly unknown growth factors delivered by bacteria. In-vitro experiments reliably show that axenic diatoms (bacteria-free) grow slower than xenic ones (containing associated bacteria), despite the provision of complete nutrient profiles in standard culture media. Microalgae synthesise and convert fatty acids (FA) into cell and thylakoid membrane lipids and energy-rich triacylglycerols. As bacteria potentially have dual effects on diatoms, such as provision of essential growth factors but competition for N and P-rich macronutrients, we tested the hypothesis that microbiome bacteria affect diatom FA profiles and result in qualitative and quantitative differences. The diatom Thalassiosira rotula was grown both, axenically and xenically, to stationary growth phase and sampled over the course of eight days. FA methylesters (FAME) profiles in algal extracts were analysed by GC-FID. Our results showed a difference in the relative FA composition as well as different concentrations of long-chain and very long-chain FA between treatments. Especially C16 FA were up to twice the concentration in axenic diatoms compared to xenic diatoms. This might indicate a disruption in mitochondrial beta-oxidation and thus less energy production. In conclusion, this demonstrates a distinct microbial effect on the diatom FA profile.
06:30 PM
THE METABOLIC EVOLUTION OF ALTEROMONAS: UNDERSTANDING THE FLOW OF CARBON WITHIN MARINE HETEROTROPHIC SYSTEMS (5490)
Primary Presenter: Michelle DeMers, Massachusetts Institute of Technology (mademers2018@gmail.com)
Alteromonas is a genus of cosmopolitan copiotrophic marine bacteria that associate with particles and are capable of metabolizing a large suite of carbon substrates. We aim to describe and understand patterns of niche partitioning underlying the metabolic diversity of this genus, and in particular to identify the drivers of metabolic innovations within Alteromonas. To this end we gathered 78 isolate genomes and 258 metagenome-assembled genomes of Alteromonas, assembled them into a pangenome and created a phylogeny from evolutionarily relevant single copy core genes. We then surveyed the leaves of this tree for the presence and absence of genes involved in core carbon metabolism, with a focus on carbon cycling and substrate degradation. Among genes involved in polysaccharide degradation, we find those for using alginate and pectin are patchily distributed across clades while those forusing laminarin are highly conserved. We also find diversity in the distribution of genes for the glyoxylate shunt and fatty acid and amino acid catabolism genes. Together these observations are beginning to illuminate the metabolic niche dimensions of Alteromonas. Finally, we find that depth of isolation or metagenome sampling correlates with clade structure and metabolic strategies, suggesting depth-based changes in particle composition may play a role in driving niche partitioning. More generally, this work deepens our understanding of the metabolic diversification of Alteromonas throughout its evolution and identifies forces that continue to shape the flow of carbon in extant marine systems.
06:30 PM
THE EFFECT OF TEMPERATURE ON THE METABOLIC EXCHANGE BETWEEN PHYTOPLANKTON AND SURROUNDING HETEROTROPHIC BACTERIA (5973)
Primary Presenter: McKenzie Powers, University of Georgia (mckpwrs@uga.edu)
Marine phytoplankton produce half of all fixed carbon on the planet, making a significant fraction available for microbial communities to utilize. This pivotal link between primary producers and heterotrophic bacteria is critical in the transformation of dissolved organic matter (DOM) in the ocean. Abiotic factors such as temperature can play an important role in governing the rate at which DOM is processed by microbial communities. However, the ways in which changing temperature will influence the production and consumption of DOM remains unknown. The impact of an altered temperature regime on the endometabolome composition of temperature-acclimated strains of the marine diatom Thalassiosira pseudonana was determined by LC-MS analysis. These data indicate higher concentrations of nucleic acid building blocks (e.g. hypoxanthine, uracil) and organic acids (e.g. 4-pyridoxic acid, 3-hydroxyanthranilic acid) at the warmest temperature (28°C), and of proline, 5’-methylthioadenosine, and abscisic acid at the coolest temperature (14°C). DOM consisting of endo- and exometabolite pools from the diatom strain was provided to a natural bacterial community, and uptake was tracked using gene expression as a proxy. Concurrent responses to altered temperature regimes by phytoplankton and their associated bacteria provide an important perspective on microbial processes in the future ocean.
06:30 PM
Element targeted method to characterize phosphorus containing metabolites using HPLC-ESIMS (7376)
Primary Presenter: Marianne Acker, Scripps Institution of Oceanography (maacker@ucsd.edu)
Phosphorus (P) is an essential nutrient for all forms of life. In the ocean, organic phosphorus is a large pool of P in surface waters sustaining the marine microbial community by meeting their P demands. Thus, when studying the marine biogeochemical P cycle, characterizing this pool is of great interest but currently limited by the lack of appropriate methods. So far, most P metabolites analyses use targeted metabolomics and have only been occasionally applied to marine samples. Marine untargeted metabolomics using liquid chromatography coupled with electrospray ionization (HPLC-ESIMS) is now well established in the field of metabolomics and has helped identify many key metabolites especially new nitrogen and sulfur metabolites. However, P metabolites remain under-characterized due to the poor ionization efficiency of P compounds, their poor retention on solid phase extraction columns (due to their high polarity), and their lack of stable isotope which prevents the use of mass search algorithms that target natural abundance isotope ratios of specific heteroatom (S, Br, Fe, Cu, etc.). To increase our knowledge of the molecular composition of marine P metabolites, we developed an HPLC-ESIMS/MS phosphorus targeted-approach based on a multiple reaction monitoring precursor-product ion method. We applied this method to DOM and POM samples and were able to characterize several new P metabolites including phosphonates which gives further evidence of the existence of a P redox cycling in the ocean.
06:30 PM
DIEL VARIABILITY OF DMSP AND DMS CONCENTRATIONS, CYCLING RATES AND GENE TRANSCRIPTS IN THE OPEN NW MEDITERRANEAN SEA (5816)
Primary Presenter: Rafel Simó, Institut de Ciencies del Mar, CSIC (rsimo@icm.csic.es)
Day-night alternation exerts an obvious rhythmic forcing on photochemical and photobiological processes, which may result in diel oscillations of the chemical-microbe networks, with consequences for biogeochemical fluxes. In the case of the algal metabolite DMSP and the trace gas DMS, previous studies have revealed that their local diel balance in the surface ocean depends on the fine interplay between microbial activities and physical forcing. We investigated the diel patterns in the production and loss rates of DMSP and DMS, sampling in lagrangian mode every 4 hours over 48 hours in open surface waters of the NW Mediterranean Sea. Incubations under natural full light and darkness allowed determination of microbial DMSP consumption rates (radioisotope addition), DMS production and consumption rates (inhibitor addition), and DMS photolysis rates (filtered seawater). These were compared with the variability of bacterial heterotrophic production and the diel transcription patterns of the known relevant genes.
06:30 PM
DYNAMICS OF CHEMICAL ALGAE-BACTERIA CROSSTALK - A MATTER OF DIEL MICRO-NICHE CONDITIONS? (7047)
Primary Presenter: Christina Roggatz, University of Bremen (croggatz@uni-bremen.de)
Communities of photosynthesising and nutrient-cycling microorganisms are fundamental to life and rely on chemical crosstalk to mediate the interactions within their community to function efficiently. In aquatic ecosystems, communities of microalgae and bacteria share micro-habitats in which the interplay of photosynthesis and respiration can cause steep gradients of pH and oxygen. Research over the past years revealed that communication chemicals of different kinds of organisms can be permanently or temporarily inactivated through chemical alteration due to pH conditions that are fluctuating on a level comparable to or even smaller than the level observed within microalgae-bacteria communities. This presentation aims to provide first insights into the hypothesis that diel abiotic gradients can temporarily modulate the essential chemical interactions that govern microalgae-bacteria communities. Besides describing the in-situ abiotic dynamics of pH and oxygen within a marine diatom-bacteria biofilm system on a diel timescale, I will illustrate how these conditions, as well as added external fluctuations, can impact the chemical communication within the biofilm community using a physical-chemical numerical model with acyl-homoserine lactone signals as an example. Combining these experimental and modelled aspects, I will outline how photosynthesis-linked abiotic conditions on a micro-scale could create timed micro-niches for activities performed by the community members and therefore temporally structure processes and community functioning at a chemical level.
06:30 PM
CHARACTERIZING OCEAN HOTSPOT METABOLITES WITH BACTERIAL MUTANTS (6048)
Primary Presenter: Mary Ann Moran, University of Georgia (mmoran@uga.edu)
Bacteria that assemble in phycospheres that surround living phytoplankton cells process a substantial proportion of ocean primary productivity, yet the identity of the metabolites driving these micron-scale carbon-cycle hotspots are poorly known. Using transposon mutant libraries of copiotrophic marine bacterium <em>Ruegeria pomeroyi</em> DSS-3, we are learning new details about its metabolite-based interactions with phytoplankton hosts and with other bacterial species sharing the phycosphere. In one example, a set of <em>R. pomeroyi</em> transporter mutants were screened for growth on metabolites known to be produced by phytoplankton but without a known bacterial transporter. This resulted in new or confirmed annotations of cognate substrates for 17 transporters. In a second example, differential growth rates of mutants inoculated as a pooled library into model phycospheres revealed specific genes necessary for <em>R. pomeroyi</em> success when interacting with other phycosphere bacteria. We learned that the bacterium relied more on uncontested substrates, competed for nitrogen in the forms of ammonium and amino acids, and obtained nucleosides via cross-feeding. Mutant libraries of ecologically-relevant bacteria can be powerful tools for generating and testing hypothesis, and for accelerating gene annotation.
SS116P Metabolites in the Chemical-Microbe Network
Description
Time: 6:30 PM
Date: 8/6/2023
Room: Mezzanine