Collaborative Research: Dimensions: The Macroalgal Microbiome in Space and Time---Maintaining Primary Producers in the Atlantic Rocky Intertidal Zone

University Of Maine, Orono ME

Investigators

Abstract

Intertidal macro algae ('seaweeds') provide habitat, shelter and food to many invertebrates and young fishes. Much is known about how intertidal algae react to natural stresses, but little is known about the natural community of bacteria associated with these algae. Past studies in the laboratory found that some 'seaweeds' disintegrate after removal of their bacteria with antibiotics suggesting these bacteria are essential to the health of their hosts. This research will examine the genetic, taxonomic, and functional aspects of biodiversity of bacteria associated with several 'seaweeds' that are particularly important to the general health of marine ecosystems. The research will determine how these bacteria change with season, position within the intertidal zone and latitudinal range. Stability or change in the bacterial species associated with a host will be examined by studying the particular bacterial genes that are present at different sampling times and by studying host responses to inoculations with particular bacteria. The work will also study whether any bacteria are inhibited by the environmental extremes found across the intertidal zone or over latitude, especially at the southern borders of a host's range where climate change may disturb the bacterial community on the host. Researchers will deposit isolates and voucher specimens into public collections, and, in collaboration with trained citizen scientists, will provide digital access to all algal materials within the University of Maine Herbarium. The multi-faceted data collected during this research will aid studies by other intertidal ecologists. How macroalgal microbiomes change in space and time is poorly known. Is there a 'cool, wet' versus a 'hot, dry' macroalgal microbiome(s)? If so, how does this affect host function? Here, microbiomes will be characterized over the vertical gradient of the intertidal zone on the Maine shore in differentially zoned species within each of two prominent genera, Fucus (rockweed) and Porphyra (laver). Contemporaneously, a trans-Atlantic study of microbiomes of the mid-zone Porphyra umbilicalis and Fucus vesiculosus will determine whether compositional changes found over an intertidal stress gradient are mirrored over the latitudinal range of mid-zoned species. If so, does this matter? This question will be answered by using shotgun metagenomic analyses to compare the genetic composition with the characterized taxonomic composition of the macroalgal microbiomes. Environmental variation associated with microbiome collections will be measured with in situ sensors and from archival and real time data available from government climate services (e.g., NOAA). The potential to detect changes over historic time will be assessed using herbarium specimens. To study bacteria that are likely to be most critical to normal structure and function of Fucus and Porphyra, the researchers will focus on bacterial isolations from spores and fertilized eggs, aided by flow cytometry and single cell genomics. To establish the criticality of these associations, microbiome-depleted embryos will be inoculated with such bacterial isolates, and the resulting interaction will be investigated by analysis of the host transcriptome with RNA-Seq. The temperature tolerance of key bacterial species (operational taxonomic units) will be established in laboratory experiments. This research will serve as an important trans-Atlantic baseline of the biodiversity of macroalgal microbiomes.