High-resolution analysis of metabolic cycles in the intertidal musselMytilus californianus

Abstract

Inhabitants of the marine rocky intertidal live in an environment that alternates between aquatic and terrestrial due to the rise and fall of the tide. The tide creates a cyclical availability of oxygen with animals having access to oxygenated water during episodes of submergence, while access to oxygen is restricted during aerial emergence. Here we performed liquid chromatography and gas chromatography-mass spectrometry enabled metabolomic profiling of gill samples isolated from the California ribbed mussel, Mytilus californianus, to investigate how metabolism is orchestrated in this variable environment. We created a simulated intertidal environment in which mussels were acclimated to alternating high and low tides of 6 h duration, and samples were taken every 2 h for 72 h to capture reproducible changes in metabolite levels over six high and six low tides. We quantified 169 named metabolites of which 24 metabolites cycled significantly with a 12-h period that was linked to the tidal cycle. These data confirmed the presence of alternating phases of fermentation and aerobic metabolism and highlight a role for carnitine-conjugated metabolites during the anaerobic phase of this cycle. Mussels at low tide accumulated eight carnitine-conjugated metabolites, arising from the degradation of fatty acids, branched-chain amino acids, and mitochondrial β-oxidation end products. The data also implicate sphingosine as a potential signaling molecule during aerial emergence. These findings identify new levels of metabolic control whose role in intertidal adaptation remains to be elucidated.

The environmentally tuned transcriptomes ofMytilusmussels

“…In a companion study, changes in metabolism were investigated by measuring changes in heart rate and by analysis of metabolite levels in the gills of the same mussels using mass-spectrometryenabled metabolomics (Connor and Gracey, 2012). The analysis of heart rates showed that animals enter a period of dramatically reduced cardiac activity, or bradycardia, during bouts of emersion, with the drop in heart rate occurring within minutes of being exposed to air.…”

“…Together, these 'omics' studies provide the most comprehensive overview to date into how transcript and metabolite levels are orchestrated in mussels under a tidal regime, and show that ∼40% of the transcriptome exhibits rhythmic changes in abundance, with 80-90% of the rhythmic transcripts exhibiting a circadian 24 h oscillation (Connor and Gracey, 2011), while rhythmic changes in metabolite abundance are associated solely with a tidal 12 h oscillation (Connor and Gracey, 2012). Given the preponderance of circadian transcriptional rhythms in the intertidal mussels, it is surprising that no metabolites were detected that oscillate with a circadian rhythm.…”

Tide-related biological rhythm in the oxygen consumption rate of ghost shrimp (Neotrypaea uncinata Milne Edwards)

“…For example, Mytilus californianus exhibits noticeable metabolic rhythms during simulated tidal cycles (Connor and Gracey, 2012). In other invertebrates, such as decapod crustaceans, several reports show the existence of biological rhythms in locomotory activity and oxygen consumption (Naylor, 2010;Palmer, 1995).…”

Metabolic profiling of mussel larvae: effect of handling and culture conditions

“…Succinate is a tricarboxylic acid cycle (TCA) intermediate and is capable of donating electrons to the electron transport chain via oxidation to fumarate by succinate dehydrogenase (SDH). Decreased expression of SDH and increased levels of succinate are indicative of oxidative stress in shellfish when oxygen availability is limited (Tuffnail et al 2009 ;Anestis et al 2010 ;Connor and Gracey 2012 ), and when organisms are exposed to toxins (Wu et al 2013a ;Hanana et al 2014 ) or pathogens (Ji et al 2013 ;Wu et al 2013b ). Elevated tissue concentrations of succinate are also indicative of poor larval quality due to lower capacity for energy production (Young et al 2015b ).…”