Adverse Environmental Perturbations May Threaten Kelp Farming Sustainability by Exacerbating Enterobacterales Diseases

Globally kelp farming is gaining attention to mitigate
land-use
pressures and achieve carbon neutrality. However, the influence of
environmental perturbations on kelp farming remains largely unknown.
Recently, a severe disease outbreak caused extensive kelp mortality
in Sanggou Bay, China, one of the world’s largest high-density
kelp farming areas. Here, through in situ investigations and simulation
experiments, we find indications that an anomalously dramatic increase
in elevated coastal seawater light penetration may have contributed
to dysbiosis in the kelp Saccharina japonica’s microbiome. This dysbiosis promoted the proliferation of
opportunistic pathogenic Enterobacterales, mainly including the genera Colwellia and Pseudoalteromonas. Using
transcriptomic analyses, we revealed that high-light conditions likely
induced oxidative stress in kelp, potentially facilitating opportunistic
bacterial Enterobacterales attack that activates a terrestrial plant-like
pattern recognition receptor system in kelp. Furthermore, we uncover
crucial genotypic determinants of Enterobacterales dominance and pathogenicity
within kelp tissue, including pathogen-associated molecular patterns,
potential membrane-damaging toxins, and alginate and mannitol lysis
capability. Finally, through analysis of kelp-associated microbiome
data sets under the influence of ocean warming and acidification,
we conclude that such Enterobacterales favoring microbiome shifts
are likely to become more prevalent in future environmental conditions.
Our study highlights the need for understanding complex environmental
influences on kelp health and associated microbiomes for the sustainable
development of seaweed farming.