Thraustochytrid fungoid protists in faecal pellets of the tunicate Pegea confoederata, their tolerance to deep-sea conditions and implication in degradation processes
S. Raghukumar et C. Raghukumar, Thraustochytrid fungoid protists in faecal pellets of the tunicate Pegea confoederata, their tolerance to deep-sea conditions and implication in degradation processes, MAR ECOL-PR, 190, 1999, pp. 133-140
During a swarm of the tunicate Pegea confoederata (salp) in the northern Ar
abian Sea, we examined their faecal pellets for thraustochytrid protists an
d bacteria to understand the role of the former in decomposition processes
in the sea. Fresh faecal pellets from surface waters contained on average 6
.58 x 10(6) thraustochytrids g(-1) dry wt, while bacterial numbers were abo
ut 3 orders of magnitude higher. Highest numbers of thraustochytrids were o
bserved when the faecal pellets were incubated at 25 degrees C for 6 d usin
g unsterilized surface sea water, as compared to 10 degrees C using sterili
zed or unsterilized water collected from 100 m depth. Our results indicate
that thraustochytrids in the water column may further colonize faecal pelle
ts. A thraustochytrid isolate cultured from such faecal pellets grew on pin
e pollen, Artemia larvae and nutrient broth, when subjected to 10 degrees C
and a pressure of 10 MPa, corresponding to 1000 m depth. It also produced
proteases when subjected to combinations of 2 pressures, 0.1 (1 atm) and 10
MPa (100 arm), and 2 temperature conditions, 30 and 10 degrees C. The resu
lts suggest that thraustochytrids found in such particulate organic matter
may actively contribute to decomposition processes not only in the surface
waters, but also under deep-sea conditions.