Biomass and community structure of the abyssal microbiota determined from the ester-linked phospholipids recovered from Venezuela Basin and Puerto Rico Trench sediments.

Extractible phospholipid fatty acids of abyssal sediment cores from three stations in the Venezuela Basin, transects between them, and a station in the Puerto Rico Trench were analyzed to determine microbial biomass and community composition. Results were compared to abyssal sediments from an area of high-energy boundary currents in the North Atlantic, and estuarine sediments from Apalachee Bay, Florida. Venezuela Basin and Puerto Rico Trench sediments were characterize by low microbial biomass, measured as phospholipid palmitic acid. Venezuela Basin sediments of three different sedimentary regimes showed a remarkably similar microbial community structure, as characterized by fatty acid profiles. Prokaryotic organisms dominated the microbial community, and fatty acids believed to be signatures of anaerobic organisms were present in greater proportions in Venezuela Basin and Puerto Rico Trench sediments than in either the North Atlantic abyssal sediments or shallow-water estuarine sediments.

Mechanical properties of glycerinated fibres from the tymbal muscles of a Brazilian cicada.

1. Some of the properties of glycerinated fibres from the synchronous tymbal muscles of the cicada Fidicina rana have been investigated.2. In the presence of suitable concentrations of ATP and calcium ions, the fibres are able to perform oscillatory work when subjected to small sinusoidal length changes in the frequency range 2-30 c/s.3. When subjected to abrupt changes in length, active fibres show a delayed increase in tension after a stretch and a delayed decrease in tension after release.4. The muscle fibres therefore show the mechanical properties characteristic of glycerinated fibres from asychronous insect flight muscles. Some implications of this finding in relation to the evolution of asynchronous muscles are discussed.