Antibacterial Activity of Antarctic Marine Phytoplankton1

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Abstract
Water and phytoplankton samples from the Weddell Sea were assayed for their antibacterial activity during the 1957–58 Argentine Antarctic Expedition. Four of seven sea water samples contained sufficient phytoplankton in volumes of 1 to 500 ml to inhibit bacterial growth. At three hydrographic stations phytoplankton retained by a coarse zooplankton net was inhibitory in concentrations as small as 100 parts per million on a wet volume basis (5 ppm dry weight basis). This antibacterial substance, which inhibited Gram positive organisms to a greater extent than Gram negative organisms, was active in fresh preparations, stable at 60°C for 30 min., labile when heat dried at 85°C for 40 min., water soluble and filterable. Phytoplankton in the stomach of euphausiids, Euphausia superba, also exhibited similar antibacterial properties. Such euphausiids, the staple diet of the penguins examined, apparently modify the gastrointestinal microflora of penguins.