In aquatic ecosystems, physical transport processes connect organisms to their environment. At the level of a single cell in the range of a few micrometers, transport via diffusion dominates. At millimeter to centimeter scales, transport via laminar flow becomes prevalent until turbulent mixing dominates. In heterogeneous aquatic environments, organisms often face substrate limitation resulting from high metabolic activity that cannot be sustained through passive transport. To overcome these limitations organisms have therefore evolved a variety of mechanisms to optimize mass transfer and navigate within heterogeneous aquatic environments. These allow them to make substrates more readily available and deal with external stressors. A prime example are cilia and flagella, which enable organisms to either seek out food or propel substrates towards themselves. Other examples include collective mixing by bacterial swarming, chemo/phototaxis, or osmotic pressure controls in plants. In recent years, a variety of methods have been developed to better understand the interaction of organisms with flow and the external environment. These methods cover chemical imaging, high-speed imaging, particle velocimetery, NMR-spectroscopy, microfluidics, schlieren, mathematical modelling and many others. We invite submission across disciplines that investigate mass transfer around organisms and within their environment. Typical organisms include corals, sponges, tunicates, ciliates, crustaceans and flagellated prokaryotes but also marine snow particles and others. The particular aim of the session is to highlight new and existing approaches and methods in which physical and biological science is combined. In discussion rounds we aim to share technologies across disciplines and inspire new lines of research.
Lead Organizer: Soeren Ahmerkamp, Max Planck Institute for Marine Microbiology, Bremen (sahmerka@mpi-bremen.de)
Co-organizers:
Klaus Koren, Aarhus University (klaus.koren@bio.au.dk)
Lars Behrendt, Science of Life Institute, Uppsala University (lars.behrendt@scilifelab.uu.se)
Presentations
06:30 PM
HETEROGENEOUS MICROENVIRONMENTS ON INDIVIDUAL SAND GRAINS ENHANCE NITROGEN LOSS (5870)
Primary Presenter: Farooq Moin Jalaluddin, Max Planck Institute for Marine Microbiology, Bremen (fjalalud@mpi-bremen.de)
Permeable sands cover more than half of the coastal and riverine environments, where they serve as major contributors to nitrogen (N) loss. The extent of this N-loss is enhanced by the occurrence of denitrification in apparently oxic sediments. This has been attributed to microbial adaptations to the frequent oscillations in oxygen (O2) availability that characterize sands. Yet, the microenvironments around individual sand grains that are important factors in controlling the microbial metabolism are only little understood. Here, we used a new non-invasive microfluidic technique that allowed us for the first time to observe O2 concentrations and distributions of microorganisms at the single sand grain level. This revealed a high heterogeneity in O2 production and consumption rates, which varied by two orders of magnitude, matching the patchy microbial colonization. We used our observations to develop a transport-reaction model to further investigate how this microbial activity shapes anoxic microenvironments in sands. This showed that anoxic microenvironments form within the boundary layer of sand grains even at O2 concentrations as high as 80 µM. Based on a new scaling relationship, we predict that more than 70% of denitrification that occurs in apparently oxic sands can be attributed to the presence of anoxic microenvironments. This study therefore indicates a previously underestimated contribution of anoxic microenvironments to N-loss by denitrification in oxic sediments.
06:30 PM
WHERE’S THE FEAST? BEHAVIOURAL RESPONSES OF MODEL MARINE PROTISTS TO DMSPc (6054)
Primary Presenter: MEDEA ZANOLI, Mediterrenean Institute of Advanced Studies (IMEDEA) (medeazanoli@gmail.com)
Micro-scale processes ubiquitously shape the marine ecosystem, from the structure of the trophic web to the fate of the chemical compounds that enter the biogeochemical cycles. In the patchy turbulent environment of the ocean, the interaction between the microorganisms at the base of the marine trophic web is mediated by the chemoresponse to ephemeral chemical stimuli. In this study, we examined the chemical responses of various model marine protists to DMSP, a naturally occurring organic sulfur compound present in most marine phytoplankton, as well as its byproducts DMS and Acrylate. The organisms studied belong to three different trophic modes: <em>Oxyrris marina</em> (an osmotroph), <em>Gyrodinium dominans</em> (a phagotroph), and <em>Karlodinium armiger</em> (a mixotroph). We analyzed the behavioral changes induced by the chemical stimuli by using a conventional capillary asset, broadly used in chemotaxis studies, along with an automated image analysis technique to track the individual trajectories of the swimming organisms. Our results indicate that all organisms exhibit a strong chemoattraction to DMSP, mild chemoattraction to DMS, and no chemorepulsion towards Acrylate, which contradicts previous studies. We also noted a chemokinetic response of <em>Gyrodinium d.</em> to DMSP, as it altered the organism's swimming behavior in terms of speed and motility patterns. These findings could offer further understanding of how marine protists utilize these compounds and provide a deeper insight on the distinct foraging strategies employed by individual organisms depending on their trophic mode.
06:30 PM
SensPIV: Simultaneous visualization of flow fields and oxygen concentrations to unravel metabolic exchange fluxes (7077)
Primary Presenter: Soeren Ahmerkamp, Max Planck Institute for Marine Microbiology (sahmerka@mpi-bremen.de)
Transport of oxygen (O2) is essential for life on Earth as it sustains aerobic organisms respiring O2. Aerobic respiration leads to the local depletion of O2, whereas diffusive and advective transport processes replenish the O2 required for biological activity. There are multiple ways in which organisms interact with or generate flow fields to optimize their O2 supply, but so far, our understanding on these complex interactions is mostly derived from simplified mathematical models. This is mainly because we lack methods that can accurately measure transport processes and O2 concentrations at the same time. Here, we present a novel method that combines microscale ratiometric and lifetime-based O2 imaging with particle velocimetry to determine O2 concentrations and flow fields simultaneously. This method, called “sensPIV”, allows to link O2 uptake to transport processes across a wide range of biological systems. We will present the application of sensPIV to study living corals, mussels and particles and show, for example, that corals use ciliary movement to link zones of photosynthetic O2 production to zones of O2 consumption. By measuring O2 concentrations and flow fields simultaneously, we provide novel insights into the interactions between biological systems and O2 transport that illustrate the connectivity between single organisms and their environment.
SS073P From Single Cells to Ecosystems Scales – Connectivity Between Microorganisms and Their Environment
Description
Time: 6:30 PM
Date: 7/6/2023
Room: Mezzanine