Effect of Temperature on Adhesion of Vibrio Strain AK-1 to Oculina patagonica and on Coral Bleaching

Abstract

Laboratory aquarium experiments demonstrated thatVibrio strain AK-1 caused rapid and extensive bleaching of the coral Oculina patagonica at 29°C, slower and less-complete bleaching at 23°C, and no bleaching at 16°C. At 29°C, the application of approximately 100 Vibrio strain AK-1 cells directly onto the coral caused 50 and 83% bleaching after 10 and 20 days, respectively. At 16°C, there was no bleaching, even with an initial inoculum of 1.2 × 108 bacteria. To begin to understand the effect of seawater temperature on bleaching ofO. patagonica by Vibrio strain AK-1, adhesion of the bacteria to the coral as a function of temperature was studied. Inoculation of 107 Vibrio strain AK-1 organisms into flasks containing 20 ml of seawater at 25°C and a fragment ofO. patagonica resulted in net levels of bacterial adhesion to the coral of 45, 78, and 84% after 2, 6, and 8 h, respectively. The adhesion was inhibited 65% by 0.001%d-galactose and 94% by 0.001% methyl-β-d-galactopyranoside (β-M-Gal). After the incubation of Vibrio strain AK-1 with the coral for 6 h, 42% of the input bacteria were released from the coral with 0.01% β-M-Gal, compared to less than 0.2% when β-M-Gal was present during the adhesion step. Adhesion did not occur whenVibrio strain AK-1 was grown at 16°C, regardless of whether the corals were maintained at 16 or 25°C, whereas bacteria grown at 25°C adhered to corals maintained at 16 or 25°C. Bacteria grown at 25°C adhered avidly to Sepharose beads containing covalently bound β-d-galactopyranoside but failed to bind if grown at 16°C. These data suggest that elevated seawater temperatures may cause coral bleaching by allowing for the expression of adhesin genes of Vibrio strain AK-1.

Role of endosymbiotic zooxanthellae and coral mucus in the adhesion of the coral-bleaching pathogen Vibrio shiloi to its host

“…Previous studies have demonstrated that V. shiloi adheres to its coral host, O. patagonica, via a L-D-galactoside-containing receptor on the coral surface [10]. The data presented here demonstrate that the receptor is present in the coral mucus and that actively photosynthesizing zooxanthellae inside the coral are required for the receptor to be present in the mucus.…”

“…We have demonstrated that the causative agent of bleaching of O. patagonica is a new species of Vibrio, Vibrio shiloi [7^9]. The infectious process requires at least ¢ve distinct and sequential steps: (i) Adhesion of the bacte-rium to the coral surface [10], (ii) penetration into the coral epidermal layer [11], (iii) di¡erentiation into a viable but not culturable (VBNC) state [12], (iv) intracellular multiplication, reaching over 10 8 bacteria per cm 3 coral tissue [11,12] and (v) production of extracellular toxins that inhibit photosynthesis, bleach and lyse zooxanthellae [13,14]. The adhesion, intracellular multiplication and toxin production steps are all temperature dependent, i.e., the necessary virulence factors are produced only when the bacteria are at high (summer) temperatures [10,15,16].…”

“…The ¢rst step in the infection process is the adhesion of V. shiloi to a L-D-galactopyranoside-containing receptor on the coral surface [10]. This step is essential for infection and subsequent bleaching because non-adhering mutants are not virulent [15].…”

Lo spessore delle linee. Quattro esercizi a partire dal disegno del piano di Genova

“…Clearly, elevated temperature and bacterial or fungal infection are not mutually exclusive. Many pathogens have the capacity to cause disease only in a host under stressful conditions: increased seawater temperature (or other environmental stress) can trigger mortality by inducing a microbe to be more virulent or the host more vulnerable Toren et al 1998).…”

Coral disease hotspots in the Caribbean

“…Coral disease hotspots can arise through a number of mechanisms driven by thermal stress. Firstly, elevated SSTs may increase the growth rate and virulence of pathogens, leading to higher pathogen densities and higher rates of infectivity , Toren et al 1998, Harvell et al 2002, Rosenberg et al 2007. Secondly, elevated SSTs may compromise coral immunity resulting in an increased number of susceptible and infected hosts (Ritchie 2006, Lesser et al 2007, Muller et al 2008, Mydlarz et al 2010, Reed et al 2010.…”