Oxyconformity in the intertidal worm Sipunculus nudus: the mitochondrial background and energetic consequences

Abstract

The energetic consequences of strict oxyconformity in the intertidal worm S. nudus were studied by characterizing the Po dependence of respiration in mitochondria isolated from the body wall tissue. The contribution of the rates of mitochondrial ROS production and proton leakiness to mitochondrial oxygen consumption and uncoupling was investigated by using oligomycin as a specific inhibitor of the ATP synthase. The maximum contribution of oligomycin independent respiration to state 3 respiration remained below 6% and showed a minor, insignificant increase at elevated Po , at a slope significantly lower than the increment of state 3 respiration.2 Therefore, Po dependent mitochondrial proton leakage or ROS production cannot explain oxyconformity. In 2 conclusion Po dependent state 3 respiration likely relates to the progressive contribution of an alternative oxidase 2 Ž . cytochrome o , which is characterized by a low affinity to oxygen and an ATPrO ratio similar to the branched respiratory system of bacteria. The molecular nature of the alternative oxidase in lower invertebrates is still obscure. ᮊ

Seasonality of energetic functioning and production of reactive oxygen species by lugworm (Arenicola marina)mitochondria exposed to acute temperature changes

“…Therefore, only approximately 10% of the cellular oxygen uptake actually drives the proton leak in lugworms. Similarly low values (<10% of state 3 respiration) were found in mitochondria isolated from the body wall tissue of a sipunculid worm (Buchner et al, 2001). So, what makes these tissues different from others?…”

Rapid mitochondrial adjustments in response to short-term hypoxia and re-oxygenation in the Pacific oysterCrassostrea gigas

“…Its role would be to maintain respiratory electron flux and cellular redox balance under metabolically downregulated conditions, or when oxygen levels within the cell start to rise because the classical respiratory chain is saturated with oxygen, minimizing the risk of oxidative stress (Tschischka et al, 2000). AOX activity has been detected in various marine invertebrates (Tschischka et al, 2000;Buchner et al, 2001;Pichaud et al, 2012), and the presence of its sequence was established in C. gigas and several bivalves (McDonald and Vanlerberghe, 2004;McDonald et al, 2009). In C. gigas an expressed sequence tag corresponding to the AOX sequence was first found in a hemocyte cDNA library coming from a bacterial challenge (Gueguen et al, 2003).…”

“…Besides systems controlling the respiratory chain, recent studies show the presence of an alternative oxidase (AOX) in hypoxiatolerant marine invertebrates (Tschischka et al, 2000;Buchner et al, 2001;Pichaud et al, 2012). AOX gene sequences were found in many invertebrates and in particular in bivalves (McDonald and Vanlerberghe, 2004;McDonald et al, 2009).…”

Impacts of hypoxia on the structure and processes in pelagic communities (zooplankton, macro-invertebrates and fish)

“…Circumstantial evidence for the presence of an alternative mitochondrial oxidase (cytochrome o) exists in lower marine invertebrates, e.g. sipunculids, annelids or bivalves (Pörtner et al, 1985;Buchner et al, 2001;Tschischka et al, 2000). This oxidase might represent an ancient mechanism of oxygen detoxification used in animals which live in hypoxic environments.…”