Mitigation of
Vibrio coralliilyticus
-induced coral bleaching through bacterial dysbiosis prevention by
Ruegeria profundi
Authors: Xu Meiting , Cai Zhonghua , Cheng Keke , Chen Guofu , Zhou Jin 
Published: March 2024

Vibrio
species are prevalent in ocean ecosystems, particularly
Vibrio coralliilyticus
, and pose a threat to corals and other marine organisms under global warming conditions. While microbiota manipulation is considered for coral disease management, understanding the role of commensal bacteria in stress resilience remains limited. Here, a single bacterial species (
Ruegeria profundi
) rather than a consortium of native was used to combat pathogenic
V. coralliilyticus
and protect corals from bleaching.
R. profundi
showed therapeutic activity
in vivo
, preventing a significant reduction in bacterial diversity in bleached corals. Notably, the structure of the bacterial community differed significantly among all the groups. In addition, compared with the bleached corals caused by
V. coralliilyticus
, the network analysis revealed that complex interactions and positive correlations in the bacterial community of the
R. profundi
protected non-bleached corals, indicating
R. profundi
’s role in fostering synergistic associations. Many genera of bacteria significantly increased in abundance during
V. coralliilyticus
infection, including
Vibrio
,
Alteromonas
,
Amphritea
, and
Nautella
, contributing to the pathogenicity of the bacterial community. However,
R. profundi
effectively countered the proliferation of these genera, promoting potential probiotic
Endozoicomonas
and other taxa, while reducing the abundance of betaine lipids and the type VI section system of the bacterial community. These changes ultimately influenced the interactive relationships among symbionts and demonstrated that probiotic
R. profundi
intervention can modulate coral-associated bacterial community, alleviate pathogenic-induced dysbiosis, and preserve coral health. These findings elucidated the relationship between the behavior of the coral-associated bacterial community and the occurrence of pathological coral bleaching.

IMPORTANCE

Changes in the global climate and marine environment can influence coral host and pathogen repartition which refers to an increased likelihood of pathogen infection in hosts. The risk of
Vibrio coralliilyticus
-induced coral disease is significantly heightened, primarily due to its thermos-dependent expression of virulent and populations. This study investigates how coral-associated bacterial communities respond to bleaching induced by
V. coralliilyticus
. Our findings demonstrate that
Ruegeria profundi
exhibits clear evidence of defense against pathogenic bacterial infection, contributing to the maintenance of host health and symbiont homeostasis. This observation suggests that bacterial pathogens could cause dysbiosis in coral holobionts. Probiotic bacteria display an essential capability in restructuring and manipulating coral-associated bacterial communities. This restructuring effectively reduces bacterial community virulence and enhances the pathogenic resistance of holobionts. The study provides valuable insights into the correlation between the health status of corals and how coral-associated bacterial communities may respond to both pathogens and probiotics.