A barophilic flagellate isolated from 4500 m in the mid-North Atlantic

Abstract

A bacterivorous, barophilic, kidney-shaped flagellate, 3.5–6 μm in length, was isolated from 4500 m in the mid-Atlantic by enrichment of water directly overlying the sediment with sterilized phytodetritus collected from the English Channel during the spring and summer. The light microscopical and electron microscopical appearances of the cell are described and used to identify it to the genus Bodo (Protozoa, Bodoninae). Bodo sp. did not grow at 1 atm and 2°C. It, however, grew under 450 atm and 2°C, with a mean relative growth rate over the exponential growth phase of 0.33 day −1, equivalent to a doubling time of 2.11 days. The flagellate was bacterivorous and had an estimated carbon conversion efficiency of bacterial carbon into flagellate carbon of 17–25%. The step in the microbial food web from bacteria to flagellate could be an important site for remineralization. Bacterial density in deep-sea phytodetritus (1–34 × 10 7 ml −1) and sediment (5–54 × 10 9 ml −1) must be sufficient to support a flagellate population. The evidence reported here of a rapidly developing bacterial and flagellate population under simulated deep-sea conditions may indicate that a microbial decomposer pathway similar to that described in shallow waters may be significant in the decomposition of sedimented biogenic particles and energy flow in the deep sea.