Susceptibility to oxidative stress of the Mediterranean demosponge Petrosia ficiformis: role of endosymbionts and solar irradiance

The effects of elevated pO(2) and irradiance as inducers of prooxidant cond itions have been investigated in the Mediterranean demosponge Petrosia fici formis (Poiret, 1789). This species lives symbiotically with the autotrophi c cyanobacterium Aphanocapsa feldmanni, the abundance of which is controlle d by the intensity of light irradiance. III the presence of symbionts, tiss ues of P. ficiformis were characterized by a general enhancement of antioxi dant defenses as compared to aposymbiotic specimens. The main differences i ncluded higher activities of several antioxidant enzymes and a greater capa bility to neutralize various forms of oxyradicals, as indicated by the tota l oxyradical scavenging capacity (TOSC) assay. Elevated pO(2), more than li ght, appeared to be the primary factor inducing prooxidant pressure in the Mediterranean sponge; in fact, irrespective of the solar irradiance experie nced by the sponge, symbiotic specimens showed comparable activities of ant ioxidant enzymes and a similar scavenging capacity towards various primary factor Mediterranean the the and a reactive oxygen species. However, the po tential toxicity of photodynamic production of reactive oxygen species was demonstrated in organisms from more irradiated sites, as the levels of anti oxidant defenses were lowered in the outer layer of the sponge. The role of enhanced antioxidant defenses in protecting symbiotic specimens, also from oxyradical-mediated toxicity of light exposure, was supported by transloca tion experiments; aposymbiotic sponges did not survive when moved to condit ions of elevated solar irradiance, while no effects were observed in symbio tic specimens if translocated and/or deprived of symbionts.