Alternate life history phases of a common seaweed have distinct microbial surface communities

Abstract

Macroalgal life histories are complex, often involving the alternation of distinct free-living life history phases that differ in morphology, longevity and ploidy. The surfaces of marine macroalgae support diverse microbial biofilms, yet the degree of microbial variation between alternate phases is unknown. We quantified bacterial (16S rRNA gene) and microeukaryote (18S rRNA gene) communities on the surface of the common intertidal seaweed, Mastocarpus spp., which alternates between gametophyte (foliose, haploid) and sporophyte (encrusting, diploid) life history phases. A large portion (97%) of bacterial taxa on the surface Mastocarpus was also present in samples from the environment, indicating that macroalgal surface communities are largely assembled from the surrounding seawater. Still, changes in the relative abundance of bacterial taxa result in significantly different communities on alternate Mastocarpus life history phases, rocky substrate and seawater at all intertidal elevations. For microeukaryote assemblages, only high intertidal samples had significant differences between life history phases although sporophytes were not different from the rocky substrate at this elevation; gametophytes and sporophytes did not differ in microeukaryote communities in the mid and low zones. By sequencing three host genes, we identified three cryptic species of Mastocarpus in our data set, which co-occur in the mid-to-low intertidal zone. In these samples, M. alaskensis sporophytes harboured distinct bacterial communities compared to M. agardhii and M. intermedius sporophytes, which were not distinguishable. Conversely, microeukaryote communities did not differ among species.

A Multi-Omics Analysis Suggests Links Between the Differentiated Surface Metabolome and Epiphytic Microbiota Along the Thallus of a Mediterranean Seaweed Holobiont

“…In the case of the seaweed Mastocarpus spp., a recent study has also highlighted the importance of the host life-cycle on microbial associated communities (Lemay et al, 2018a). In connection with our study, the sexual and even the growth state of the algal host could be considered as key factors when studying seaweed microbial communities.…”

“…(Lemay et al, 2018a,b), a clear discrimination was observed between overall algal, planktonic, and rocky communities. Dissimilarities between seawater and biofilms underlined the specificity of the ecological niche that represents the life at a surface (Flemming et al, 2016), including algal surface (Lemay et al, 2018a;Sneed et al, 2015). The specificity of algal surface microbiota with respect to that found on rocky biofilms in similar environmental conditions strengthens the hypothesis of an active role of the algal host in the selection of epiphytic communities.…”

Cultivating the Macroalgal Holobiont: Effects of Integrated Multi-Trophic Aquaculture on the Microbiome of Ulva rigida (Chlorophyta)

“…This genus has been described to be present all year long in brown algae such as Mastocarpus sp. (in gametophyte and sporophyte) and Nereocystis luetkeana (Chen and Parfrey, 2018;Lemay et al, 2018). One of the 24 ASVs belonging to the Granulosicoccus genus is the most abundant ASV (7.9%) in the whole dataset.…”

“…There were further indications that microbial community structure and composition can be driven by changes in the physiological and morphological traits showed during the life cycle phases of the host, as seen in the case of brown and red algal species, such as Laminaria hyperborea and Mastocarpus spp. (Bengtsson et al, 2010;Lemay et al, 2018). Another important structuring factor is the physiological condition of the host (such as healthy or stressed), as it can influence microbial community assembly processes to a larger extent than the environmental variables do, described for the brown alga Ecklonia radiata (Marzinelli et al, 2015(Marzinelli et al, , 2018.…”

“…Molecular tools are thus necessary to solve taxonomic and cladistic hurdles such as the unification of the Ulva and Enteromorpha clades or, at the species level, Ulva compressa with Ulva mutabilis (Hayden et al, 2003;Steinhagen et al, 2019a,b). Although Ulva can be cultivated under standardized, small-scale laboratory conditions in the presence of a designed microbiome with just two essential bacterial strains (Wichard, 2015), macroalgae show variations in its associated natural microbiome along the different developmental stages of their complex life cycles (Lemay et al, 2018).…”