Ammonia removal mitigates white plague type II in the coral Pocillopora damicornis.

White Plague Type II (WPL II) is a disease increasingly affecting scleractinian coral species and progresses rapidly. However, the etiological pathogen and remedy remain elusive. In this study, transmission experiments demonstrated that Aureimonas altamirensis and Aurantimonas coralicida, representing the WPL II pathogens, could infect Pocillopora damicorni. The infection produced selected pathological symptoms, including bleaching, tissue loss, and decolorization. Furthermore, ammonia degradation significantly reduced the severity of infection by these pathogens, indicating that ammonia may be a virulence factor for WPL II. Coral microbiome analysis suggested that ammonia degradation mediates the anti-white plague effect by maintaining the density of Symbiodiniaceae and stabilizing the core and symbiotic bacteria. Aureimonas altamirensis and Aurantimonas coralicida have been shown to cause diseases of P. damicornis, with ammonia acting as a virulence factor, and ammoniac degradation may be a promising and innovative approach to mitigate coral mortality suffering from increasing diseases.