ASLO Contributed Session.
Lead Organizer: Isabel Ferrera, Spanish Institute of Oceanography (isabel.ferrera@ieo.csic.es)
Co-organizers:
Presentations
05:00 PM
SHIFTING GRAZING IMPACTS ON PICOPLANKTON POPULATIONS ACROSS AN OCEAN PRODUCTIVITY GRADIENT (6167)
Primary Presenter: Michael Landry, University of California, San Diego (mlandry@ucsd.edu)
Picophytoplankton populations (Prochlorococcus, Synechococcus and picoeukaryotes) are dominant primary producers in the open ocean and projected to increase in importance with climate change. Their fates can vary, however, with microbial food web complexities. In the California Current Ecosystem (CCE), picophytoplankton biomass and abundance peak in waters of intermediate productivity and decrease at higher production. Using experimental data from eight cruises crossing the pronounced CCE trophic gradient, we tested the hypothesis that these declines are driven by intensified grazing on heterotrophic bacteria passed to similarly sized picophytoplankton via shared predators. Results confirm previously observed distributional patterns as well as significant increases in bacterial abundance, cell growth rate and grazing mortality with primary production. Mortalities of picophytoplankton, however, diverge from the bacterial mortality trend such that relative grazing rates on Synechococcus compared to heterotrophic bacteria decline by 12-fold between low and high productivity waters. The large shifts in mortality rate ratios are not explained by size variability, but rather suggest high selectivity of grazer assemblages or tightly coupled tradeoffs in microbial growth advantages and grazing vulnerabilities. These findings challenge the long-held view that protistan grazing mainly determines overall biomass of microbial communities while viruses uniquely regulate diversity by “killing the winners”.
05:15 PM
Increase in heterotrophic bacteria biomass with macrophyte DOM rather than warming in the Red Sea (4961)
Primary Presenter: Xose Anxelu G. Moran, King Abdullah University of Science and Technology (xelu.moran@kaust.edu.sa)
We investigated the response of heterotrophic bacterioplankton to the addition of macrophytic dissolved organic matter (DOM) and temperature in the central Red Sea by adding ca. 40 µmol C L-1 of leachates obtained from seagrass and mangrove leaves to natural bacterial communities and incubating them at 3 temperatures spanning 6°C around the in situ value (25.5°C). Seagrass and mangrove DOM, important allochthonous sources in tropical oligotrophic regions, had distinct chemical characteristics compared to unamended seawater, with mangrove substrates containing comparatively more nitrogen and protein-like fluorescent DOM than seagrass. Specific growth rates increased approximately 2-fold in the seagrass and mangrove treatments (1.0 and 0.8 d-1, respectively) relative to the seawater control (0.4 d-1). The biomass of heterotrophic bacteria generally reflected µ changes, reaching maximum values of 16.8 and 17.3 µg C L-1 in the seagrass and mangrove treaments, respectively, compared to just 2.6 µg C L-1 in seawater. The increase in specific growth rates due to experimental warming followed the metabolic theory of ecology, mostly as a result of enhanced exoenzymatic activity, while cell size decreased as predicted by the temperature-size rule (mean -3% per °C increase). Although the labile nature of the specific seagrass and mangrove DOM leachates was clearly demonstrated, we conclude that Red Sea heterotrophic bacteria will have limited capability to increase their biomass as a consequence of future warming, even in the presence of high loadings of macrophytic DOM.
05:30 PM
GROWTH RATES OF MARINE PROKARYOTES ARE EXTREMELY DIVERSE, EVEN AMONG CLOSELY RELATED TAXA (4970)
Primary Presenter: Ona Deulofeu Capo, Institut de Ciències del Mar (ICM-CSIC) (odeulofeu@icm.csic.es)
Marine prokaryotes play crucial roles in ocean’s biogeochemical cycles, being their contribution largely determined by their growth rates. To improve our understanding of microbial communities’ dynamics and structure, we estimated prokaryotic growth rates at high resolution, the amplicon sequence variant (ASV) level, using manipulation experiments in each of the four astronomical seasons with different treatments that reduced limiting growth factors such as predators, nutrient availability, viruses and light. Single-ASV-based growth rate calculations showed a continuous range of values, reaching almost 10 day-1. Mean growth rates per treatment increased as limiting factors were removed, and changed seasonally. Results revealed significant variability in growth rate distribution patterns even within closely related ASVs, and with no general taxonomic coherence observed after removal of each growth limiting factor. Reduction of these factors showed that most responsive ASVs were rare, and formed a pool of taxa with the potential to rapidly respond to environmental changes. In essence, our results highlight the significance of rare-responsive taxa often overlooked in whole-community studies and suggest high dynamism in marine microbial communities with a strong capacity to adapt to changing environments.
05:45 PM
Winter-spring transition of microbial communities and interactions in a large shallow lake (6913)
Primary Presenter: Andras Hidas, Centre for Ecological Research (hidasandris@gmail.com)
Shallow lakes are highly sensitive ecosystems that are susceptible to changes in their physical, chemical, and biological properties. In this study, we investigated the changes in the phytoplankton and bacterioplankton communities from January to early April in lake Balaton, the largest shallow lake of Central Europe using a multi-approach investigation. Samples were taken weekly from the lake’s three distinct sites. The composition and quantity of phytoplankton were identified by light microscopy. 16S and 18S eDNA amplicon sequencing were used to identify planktonic bacteria, archaea, and eukaryotic phytoplankton. Co-occurrence network analysis was applied to assess time-shifted interactions. Our results showed that the phytoplankton and bacterioplankton communities in the lake achieved significant changes over the study period. Specifically, the change of relative abundance of characteristic freshwater bacteria (e.g., acI-A, acI-B, LD12) indicated a temporal shift in the composition of the communities. Shifts in the phytoplankton community structure were coupled with the abundance changes of the members of bacterioplankton. Overall, our study demonstrated the potential of a multi-approach method, combining high-throughput sequencing, microscopy, and network analysis, to better understand the dynamics of phytoplankton and bacterioplankton communities in shallow lakes.
06:00 PM
Staying below the radar: unraveling a new family of ubiquitous non-tailed temperate vibriophages and implications for their bacterial hosts (5386)
Primary Presenter: Mathias Middelboe, Københavns Universitet, Biologisk Institut (mmiddelboe@bio.ku.dk)
Bacteriophages are the most abundant biological entities in the oceans and play key roles in bacterial activity, diversity and evolution. While extensive research has been conducted on the role of tailed viruses (Class: Caudoviricetes), very little is known about the distribution and functions of the non-tailed viruses (Class: Tectiliviricetes). The recent discovery of the lytic Autolykiviridae family demonstrated the potential importance of this structural lineage, emphasizing the need for further exploration of the role of this group of marine viruses. Here we report the novel family of temperate phages under the class of Tectiliviricetes, which we propose to name “Asemoviridae” with phage NO16 as a main representative. These phages are widely distributed across geographical regions and isolation sources and found inside the genomes of at least 30 species of Vibrio in addition to the original V. anguillarum isolation host. The interactions between the NO16 phage and its V. anguillarum host were linked to cell density and phage-host ratio. High cell density and low phage predation levels were shown to favour the temperate over the lytic lifestyle for NO16 viruses, and their spontaneous induction rate was highly variable between different V. anguillarum lysogenic strains. NO16 prophages coexist with the V. anguillarum host in a mutualistic interaction by rendering fitness properties to the host, such as increased virulence and biofilm formation through lysogenic conversion, likely contributing to their global distribution.
06:15 PM
RECOVERING THE MISSING LINKS: THE MODELING OF VIRUS-HOST INFECTION NETWORKS IN SILICO (6032)
Primary Presenter: Gaylord Bastien, University of Michigan (gbastien@umich.edu)
Our ever-expanding capacity for genome sequencing has allowed for the discovery of millions of novel viruses from metagenomic data. Yet the most important information about those viruses is lost during sequencing: which microbial populations do they infect? Without this information, our ability to describe and understand the impact of viruses on their microbial communities have been severely limited. To remedy this gap, we developed a model that can resolve virus-host infection networks in silico. We first collected and digitized from published literature a total of 8,849 lab-verified virus-host interactions (infection or non-infection) at the species level, the most comprehensive host range dataset compiled to date. This data was used to assess the strength of previously-described coevolutionary signals between viruses and their hosts. We demonstrated that, relative to their host(s), viruses have both a tendency to ameliorate their k-mer profiles while remaining AT-rich. We then used this host range data to train a machine learning model that can predict the complete network of virus-host interactions. This is in contrast with recently published models that predict the most likely taxa a virus can infect. Furthermore, our machine learning model has an accuracy of 87% in predicting infection and non-infection at the species level, surpassing both the accuracy and sensitivity of existing prediction models. With this model, we can start predicting virus-host infection networks, characterize those network properties, and describe how they correlate with environmental factors.
CS026 Microbial ecology and physiology
Description
Time: 5:00 PM
Date: 5/6/2023
Room: Sala Portixol 1