Stability of the coral SML microbiome under heat stress
Thermal stress decreased coral-algal physiological performance and
caused significant compositional and functional changes in the
microbiome of P. strigosa , indicating holobiont dysbiosis (Levy
et al. 2017). According to the AKP for animal microbiomes, stressful
conditions disrupt the ability of the holobiont to regulate the
microbial community composition, resulting in an increase in
dissimilarity (i.e., dispersion, β-diversity) among microbiomes
experiencing dysbiosis (Zaneveld et al. 2017). Therefore, the AKP
predicts an unstable and stochastic microbiome composition on hosts that
were exposed to acute stress or disease, including corals under heat
stress (Zaneveld et al. 2016, 2017; Ahmed et al. 2019). However, our
results showed that β-diversity decreased in heat-stressed microbiomes
at the level of bacterial genera, stress response, nitrogen metabolism,
and sulfur metabolism genes (Fig.1). Heat-stressed coral SML microbiomes
formed a cluster with the highest similarity among all metagenomes
analyzed. The relative abundance of specific bacterial genera (Fig. 2)
and gene functions (Fig. 3) changed consistently across coral replicates
that were exposed to the heat treatment, while in the ambient treatment
these changes were more variable and not significantly different from
pre-treatment coral microbiomes. Diversity (H’) remained high both in
ambient and heat conditions (Supplemental Tab. 2). Here we present a
case for heat stress having a more stable and deterministic effect on
coral microbiomes at taxonomic and functional level, in opposition to
the AKP.