Aquatic biofilms are subjected by multiple stressors and their responses to such perturbations are a growing concern for aquatic scientists. Here, we understand stress or perturbation as a measurable change in ecosystems that is caused by chemical, physical or biological anthropogenic pressures. In freshwater and brackish ecosystems, microbial biofilms are key players at the base of trophic networks and, due to their small size and fast generation time, they respond very quickly to environmental changes, performing as indicators of the ecosystem status. In turn, depending on the type and intensity of the stressor microbial biofilms could harbour or be conduit of mixtures of contaminants and/or microorganisms released in the receiving media, becoming barriers or drivers of environmental changes. The main goal of the session is to understand how aquatic microbial biofilms respond to stressors (or multiple stressors) and their potential to act as early warning indicators of ecosystem health. This session welcomes presentations that contribute to elucidating the effects of pollution (e.g., pharmaceutical residues, heavy metals, nutrient loadings, organic contaminants, microplastics, pesticides…) climate change (e.g., warming waters, increase in salinity, changes in precipitation patterns, land uses, droughts, extreme events) or biological stressors (e.g., invasive species) on microbial aquatic biofilms. This includes evidence from field, laboratory and theoretical or modelling based studies. Talks will encompass research conducted over broad spatial and temporal scales to create a comprehensive picture of the current knowledge base. It is worth mentioning that in an increasingly changing future, knowing how microbial communities – and their functions – respond to it will help us to predict the impacts of stressors in aquatic ecosystems.
Lead Organizer: Giulia Gionchetta, Eawag (giulia.gionchetta@eawag.ch)
Co-organizers:
Nuria Perujo, UFZ Helmholtz Center for Environmental Research (nuria.perujo-buxeda@ufz.de)
Anna Freixa, ICRA Catalan Institute for Water Research (afreixa@icra.cat)
Presentations
08:30 AM
AQUATIC BIOFILMS: A SUITABLE MODEL FOR UNDERSTANDING EFFECTS OF SINLGE AND COMBINED STRESSORS ACROSS BIOLOGICAL SCALES? (6093)
Primary Presenter: Mechthild Schmitt-Jansen, Helmholtz Centre for Environmental Research - UFZ (mechthild.schmitt@ufz.de)
Aquatic biofilms, also referred to as the "microbial skin" of aquatic ecosystems, play a key role in various ecosystem functions such as primary production or degradation of dissolved organic material and pollutants. They are situated in boundary layers such as the interstitium or the plastisphere and are therefore exposed to various stress factors. However, despite their important ecological role and recognized value for bioindication, their responses to multiple stressors are poorly understood. In this presentation recent findings of biofilm community responses to single and combined stressors at different biological scales will be presented. Stress responses manifest at levels of regulation, acclimation and adaptation/microevolution. Unraveling these processes requires approaches from the molecular/biochemical to structural and functional level. Recent biofilm studies on stress responses across scales, as well as the challenge of how to compare these responses will be discussed. A key concept for understanding interactions between multiple stressor effects, the concept of stress-induced community tolerance, will be illustrated. The studies will be framed within the concept of co-tolerance to understand resilience mechanisms to combined stressors and outline the consequences of induced tolerance and the associated fitness costs for ecosystem functions.
08:45 AM
Sediment bacterial metacommunities in temporary rivers (6309)
Primary Presenter: Anna Freixa, Catalan Institute for Water Research (ICRA) (afreixa@icra.cat)
The structure of bacterial metacommunities in river networks results from the balance between dispersal (mostly from upstream or from the nearby land) and environmental selection of local communities. Temporary river networks experience hydrological phases of drying and rewetting which may interfere in the dispersal and species sorting processes between habitats. We investigated the structure of river bacterial assemblages (through amplicon sequencing of the 16S rRNA gene) colonizing streambed sediments and floodplain habitats (4 different habitat types) in two river reaches (Permanent vs Intermittent) differing in their hydrology during 4 hydrological periods (encompassing the expansion, contraction, fragmentation, and non-flow phases). Our results indicate that environmental selection was the major structuring mechanism of sediment bacterial communities. We found high species turnover across habitats permanently and intermittently connected by water flow. Local communities were filtered by the specific environmental features of each habitat type. Isolated pools, for instance, favored habitat specialists within several exclusively bacterial taxa from aquatic habitats, while drying areas favoured the occurrence of taxa of terrestrial origin. Given that climate change is increasing the duration of drying periods, we may expect a future homogenisation of bacterial communities, corresponding to the lower duration of aquatic habitats.
09:00 AM
CHARACTERIZING THE RESILIENCE AND ADAPTATION OF ALPINE STREAM BIOFILM COMMUNITIES TO CLIMATE CHANGE (5377)
Primary Presenter: Martina Gonzalez Mateu, EPFL (martina.gonzalezmateu@epfl.ch)
Biofilms conform the dominant microbial lifestyle in alpine streams where they are major contributors to carbon and nutrient cycling. However, relatively little is known about their adaptive capacity to climate change as water temperature rises and hydrological conditions change. We set up a field experiment to evaluate how these changing conditions influence biofilm microbial community composition in glacier-fed streams. Biofilm bacteria were exposed to +2°C and varying hydrological flows for four months in experimental flumes, and samples were collected weekly throughout the course of the experiment for16S and 18S rRNA sequencing. We additionally isolated ~400 bacteria from these biofilms and performed phenotypic and genetic characterization of over 100 of these to elucidate which traits might enable their resilience to changing environmental conditions. We found that bacterial communities shifted over the duration of the field experiment, and both higher temperature and changes in flow regime had a significant effect on community composition. Isolates characterized thus far belonged to 41 different genera including some relatively abundant in our communities such as Sphingomonas, Rhodoferax, Polaromonas and Flavobacterium. Most isolates exhibited psychrophilic growth traits and showed at least some level of desiccation tolerance. Results from this initial study will guide efforts to assemble synthetic communities that will increase our understanding of how phenotypic and genetic traits relate to community resilience in the face of environmental change.
09:15 AM
STREAMBED RESPONSES TO DROUGHT: TRADE-OFF BETWEEN RESISTANCE STRATEGIES AND MICROBIAL FUNCTIONAL FINGERPRINTS (6429)
Primary Presenter: Anna Romaní, University of Girona (anna.romani@udg.edu)
Severity and frequency of meteorological and hydrological droughts have increased worldwide affecting river functioning. In the Mediterranean climate region, the occurrence of wet and dry phases favors the adaptation of microbial streambed communities to intermittency. However, the prolonged periods of drought may determine a strong effect on streambed community structure, composition and functions, compromising the whole ecosystem functioning. This study investigates whether and to what extent the hydrological history affect streambed microbial resistance responses (i.e. production of extracellular polymeric substances - EPS, and carotenoids) and/or their functional fingerprinting (i.e. heterotrophic functional diversity by carbon substrate utilization profiles). We analyzed streambed surface sediments from a network of 37 sites in the Mediterranean region (NE Spain), including a wide range of hydrological history (perennial and temporary streams) previously monitored over one year. We hypothesized that drought duration would cause a decrease in heterotrophic functional diversity and a greater investment of energy to resistance strategies such as EPS production. Results showed no differences in heterotrophic functional diversity among sites but distinct functional fingerprinting among hydrological categories. When analyzing samples from intermittent sites, the longest drought sites showed the largest amount of EPS, while EPS in perennial sites was highly variable. Results suggest that extreme drought imposes strict conditions constraining streambed structure and function.
09:30 AM
DROUGHT EFFECTS ON THE EXTRACELLULAR MATRIX OF HYPERSALINE LAKES’ BIOFILMS STUDIED WITH FLUORESCENT LECTIN BINDING ANALYSIS OF GLYCOCONJUGATES (6392)
Primary Presenter: Judit Boadella, University of Girona (judit.boadella@udg.edu)
Biofilms in hypersaline shallow lakes are exposed to extreme conditions of water scarcity. To cope with stressors, microorganisms develop protection structures like a matrix of extracellular polymeric substances (EPS). Understanding EPS in these naturally-stressed habitats is key to predict how climate change may affect some ecosystems. This study focuses on how drought affects the structural properties of the EPS from hypersaline lakes. Chiprana and La Muerte are two hypersaline lakes in NE Spain that naturally dry out during summer. Biofilm samples were taken when they had surface water (wet treatment) and half of the samples were left to dry out for 45 days (dry treatment). Glycoconjugate patterns within the EPS were studied by Fluorescent Lectin Binding Analysis (FLBA) with Laser Scanning Microscopy (LSM). Structural patterns of the stained glycoconjugates were classified as associated to: cyanobacteria, bacterial clusters, filaments, and a cloud-like shape. Differences between sites were higher than differences between treatments. Specifically, higher glycoconjugates volume and cloud-like shaped EPS, and lower EPS associated to bacteria and filaments in La Muerte compared to Chiprana could be explained by environmental differences (e.g. Chiprana receives water from a permanent lake) that may result in distinct microbial communities inhabiting each lake and so different proportions in the EPS patterns. Differences between wet and dry treatments were minimal and only detected in Chiprana, showing the high resilience potential of these biofilms towards drought.
09:45 AM
Buffer against nutrient stress in streams: What regulates the strength of top-down control of autotrophic biofilms? (7005)
Primary Presenter: Markus Weitere, Helmholtz Centre for Environmental Research - UFZ (markus.weitere@ufz.de)
Nutrient pollution can lead to excessive growth of autotrophic biofilms (“benthic eutrophication”) with severe consequences for riverine ecosystems. However, there is large variation in the relationship between nutrients availability and algae biomass showing that some ecosystems can cope with elevated nutrients better than others. Besides nutrients, top-down pressure on algae plays an important role for the control of eutrophication. While the general phenomenon has been investigated extensively, it is still unresolved, which variables explain the strength of biofilm top-down control and ultimately the resilience of ecosystems towards nutrient stress. We here present a series of laboratory and mesocosm (stream bypass) experiments on different scales and different organizational levels. We test the control of grazing pressure on natural autotrophic biofilms communities by the snail Ancylus fluviatilis. In a first short-term experiment, we demonstrate that the nutrient stoichiometry of the resources and correspondingly of the algal community alters the grazing pressure due to compensatory feeding behaviour. In subsequent longer-term experiments, we addressed the roles of biofilm community composition, grazer behaviour and feedback between resources and grazer growth for the overall strength of the top-down control. Together, the results show how both nutrient quantity and nutrient quality directly and indirectly alter the ability of grazers to control eutrophication and reveal underlying mechanisms how the biofilm-grazer system can buffer adverse effects of nutrients.
SS074A Aquatic Biofilms Under Stress: Barriers or Drivers of Environmental Changes
Description
Time: 8:30 AM
Date: 8/6/2023
Room: Sala Menorca A