Bacillus coagulans
restores pathogen-induced intestinal dysfunction via acetate–FFAR2–NF-κB–MLCK–MLC axis in
Apostichopus japonicus
Authors: Song Mingshan , Zhang Shanshan , Zhang Zhen , Guo Liyuan , Liang Weikang , Li Chenghua , Wang Zhonghua 
Published: June 2024

ABSTRACT

Skin ulceration syndrome (SUS) is currently the main disease threatening
Apostichopus japonicus
aquaculture due to its higher mortality rate and infectivity, which is caused by
Vibrio splendidus
. Our previous studies have demonstrated that SUS is accompanied by intestinal microbiota (IM) dysbiosis, alteration of short-chain fatty acids (SCFAs) content and the damage to the intestinal barrier. However, the mediating effect of IM on intestine dysfunction is largely unknown. Herein, we conducted comprehensive intestinal microbiota transplantation (IMT) to explore the link between IM and SUS development. Furthermore, we isolated and identified a
Bacillus coagulans
strain with an ability to produce acetic acid from both healthy individual and SUS individual with IM from healthy donors. We found that dysbiotic IM and intestinal barrier function in SUS recipients
A. japonicus
could be restored by IM from healthy donors. The
B. coagulans
strain could restore IM community and intestinal barrier function. Consistently, acetate supply also restores intestinal homeostasis of SUS-diseased and
V. splendidus
-infected
A. japonicus
. Mechanically, acetate was found to specifically bind to its receptor-free fatty acid receptor 2 (FFAR2) to mediate IM structure community and intestinal barrier function. Knockdown of FFAR2 by transfection of specific FFAR2 siRNA could hamper acetate-mediated intestinal homeostasis
in vivo
. Furthermore, we confirmed that acetate/FFAR2 could inhibit
V. splendidus
-activated NF-κB–MLCK–MLC signaling pathway to restore intestinal epithelium integrity and upregulated the expression of ZO-1 and Occludin. Our findings provide the first evidence that
B. coagulans
restores pathogen-induced intestinal barrier dysfunction via acetate/FFAR2–NF-κB–MLCK–MLC axis, which provides new insights into the control and prevention of SUS outbreak from an ecological perspective.

IMPORTANCE

Skin ulceration syndrome (SUS) as a main disease in
Apostichopus japonicus
aquaculture has severely restricted the developmental
A. japonicus
aquaculture industry. Intestinal microbiota (IM) has been studied extensively due to its immunomodulatory properties. Short-chain fatty acids (SCFAs) as an essential signal molecule for microbial regulation of host health also have attracted wide attention. Therefore, it is beneficial to explore the link between IM and SUS for prevention and control of SUS. In the study, the contribution of IM to SUS development has been examined. Additionally, our research further validated the restoration of SCFAs on intestinal barrier dysfunction caused by SUS via isolating SCFAs-producing bacteria. Notably, this restoration might be achieved by inhibition of NF-κB–MLCK–MLC signal pathway, which could be activated by
V. splendidus
. These findings may have important implications for exploration of the role of IM in SUS occurrence and provide insight into the SUS treatment.