Healthy corals maintain Vibrio in the VBNC state

Abstract

Vibrio species play an important role in the health and disease of corals. To gain a better understanding of the interactions between Vibrio and coral holobionts we examined the growth of Vibrio in the mucus of the coral Oculina patagonica while the mucus was attached and detached from the coral. Fresh mucus contained ca. 10(2) Vibrio cfu ml(-1) , representing c. 1% of the total viable count. Incubation of detached mucus resulted in a 50 000-fold increase in Vibrio cfu from 1 to 4 h, corresponding to 60% of the total viable counts. This large increase in Vibrio would require an unreasonable doubling time of 11 min. Furthermore, the total microscopic bacterial count increased only 17-fold during the 1-4 h incubation period. These data led to the conclusion that Vibrio species in the mucus were largely in the VBNC state when attached to the coral and 'resuscitated' when the mucus was detached from the coral. We suggest that the coral signal for maintaining Vibrio in the VBNC state is diffusible and unstable. Maintenance of Vibrio in the VBNC state did not require photosynthetic products of the coral holobiont. Vibrio species in the VBNC state may contribute to the health of corals by preventing infections by pathogens.