Predictable Changes in Eelgrass Microbiomes with Increasing Wasting Disease Prevalence across 23° Latitude in the Northeastern Pacific

Abstract

The roles of marine microbiomes in disease remain poorly understood due, in part, to the challenging nature of sampling at appropriate spatiotemporal scales and across natural gradients of disease throughout host ranges. This is especially true for marine vascular plants like eelgrass ( Zostera marina ) that are vital for ecosystem function and biodiversity but are susceptible to rapid decline and die-off from pathogens like eukaryotic slime-mold Labyrinthula zosterae (wasting disease).

The effect of warming on seagrass wasting disease depends on host genotypic identity and diversity

“…For example, Cellvibrionaceae are cell‐wall degraders that could either enhance L. zosterae spread or respond to the presence of dead cells (Egan & Gardiner, 2016). ASVs in this family were consistently associated with wasting disease lesions in large‐scale surveys across the West Coast of the USA (Beatty et al, 2022, mSystems ), suggesting they are worthy of additional attention in the temperature–eelgrass– Labyrinthula interaction. It is also worth noting that similar but distinct strains are likely to have different effects: for example, one strain of Maribacter differed among genotype groups, but seven other ASVs identified as Maribacter showed no differences.…”

“…It is also worth noting that similar but distinct strains are likely to have different effects: for example, one strain of Maribacter differed among genotype groups, but seven other ASVs identified as Maribacter showed no differences. More targeted approaches looking at the microbiome within lesions and during lesion development across genotypes might yield more information about microbiome–pathogen–genotype interactions (Beatty et al, 2022; Hurtado‐McCormick et al, 2021). We did not sequence microbiome samples from polycultures; thus, we cannot address whether microbiome‐related mechanisms (e.g., a reservoir of putatively protective microbes in resistant genotypes or an exchange of microbes among resistant and susceptible genotypes) could underlie the observed dilution effect under warming (Barbosa et al, 2009).…”

“…In addition, eelgrass has genetic variation for key functional traits related to thermal tolerance (DuBois et al, 2021, 2022; Reusch et al, 2005; Reynolds et al, 2016), as well as traits such as the production of chemical defenses and the relative investment in growth versus storage that can affect plant carbon balance (Abbott et al, 2018; DuBois et al, 2019, 2020; Hughes et al, 2009). Additionally, eelgrass microbiomes vary as a function of temperature and disease status (Beatty et al, 2022), and potentially plant genotype (J. Stachowicz, unpublished data), suggesting a potential direct or indirect role for microbiota in host–parasite dynamics. All of these processes potentially affect wasting disease prevalence and/or intensity (Groner et al, 2016; Zidorn, 2016), suggesting that individual genotypes may vary in disease susceptibility.…”

“…In addition, genotypes with longer leaves would be expected to have higher L. zosterae prevalence due to greater leaf‐to‐leaf contact and resulting increased parasite transmission (Muehlstein, 1992). Finally, we hypothesized that particular microbial taxa previously documented to be associated with disease status in the field would be associated with L. zosterae infection and more prevalent at warmer temperatures (Beatty et al, 2022).…”

Local environment drives rapid shifts in composition and phylogenetic clustering of seagrass microbiomes

“…Both leaves and roots show geographic structure 31 , 32 , though this is more limited in roots than leaves. Potentially functionally important sulfide oxidizing bacteria are widespread and abundant in communities collected from roots 33 , and there is association between leaf microbial taxa including cell-wall degrading bacteria and the abundance of pathogens 34 and disease severity 35 . No work in eelgrass to date has tested the role of host versus environment in microbial community structure but we know that there are strong differences in host genotypic composition, genetically-based traits, and environment on spatial scales less than 1km 36 – 39 and that the plant microbiome varies on local, regional and global scales 31 , 35 .…”