Isolation and Characterization of Filterable Marine Bacteria

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Abstract
By a process of double filtration of seawater, first through a membrane filter with a pore diameter of 0.45[mu] and then through a membrane filter with a pore diameter of 0.22[mu], it was possible to isolate on the surface of the latter membrane a group of marine organisms not usually encountered by conventional techniques of pour plates or one-stage filtration. Many of the isolates could not be identified, but the largest single group belonged to the genus Spirillum; other isolates were placed in the genera Leucothrix, Flavobacterium, Cytophaga, and Vibrio. A group of four organisms which was not identified was charac-terized by the formation of large, club-shaped cells, 20 to 30[mu] long. Of the 25 strains studied in detail, 22 required seawater for growth and 8 retained their filterable property after cultivation. No filterable bacteria were isolated from terrestrial samples.