Aeromonas hydrophila PepO outer membrane endopeptidase activates human big endothelin-3 in vitro and induces skin ulcer in goldfish (Carassius auratus)

In Aeromonas hydrophila, the gram-negative bacterial fish pathogen, PepO constitutes the thermoregulated outer membrane M13 family zinc endopeptidase, which is expressed maximally at 16 °C and is down-regulated above 30 °C. Cultivation of A. hydrophila at 16 °C enabled it to activate big endothelin (ET), the vasoconstrictor and ulcerogenic peptide naturally secreted from human vascular endothelial cell (HUVEC) culture. Furthermore, A. hydrophila PepO in vitro shows strong enzymatic preference for human big ET-3 rather than big ET-1 and big ET-2. At water temperature of 16 ± 1 °C, intramuscular infection of goldfish, Carassius auratus, with wild-type A. hydrophila led to development of a pathognomonic big ulcer at the injection site while the PepO deficient mutant strain lost both its big ET endopeptidase activity in vitro as well as its ulcerogenic property in vivo. This is the first report of expression, subcellular localization and functional analysis of PepO metalloendopeptidase in A. hydrophila.