Water-soluble Factors in the Nutrition of Oxyrrhis Marina

Oxyrrhis marina Dujardin is a non-photosynthetic dinoflagellate whose obvious mode of nutrition is phagotrophy. The method of feeding was described by Barker (1935). It is an extremely euryhaline and hardy organism and is apparently very successful in brackish habitats such as supralittoral rock pools and ditches (Droop, 1953a). Owing to the ease with which it can be cultivated Oxyrrhis is a choice for the initial study of phagotrophy among the predominantly plant-like Dinoflagellata. Axenic cultures (i.e. cultures free from other organisms of any kind) are required for nutritional studies, but they are not often easily established when the subject is phagotrophic. Oxyrrhis was no exception, despite the ease with which it can be kept in the laboratory. Bacteria-free cultures of a Finnish race were established in 1951 (Droop, 1953b), but there then appeared to be a requirement for a living food organism such as a yeast or alga. Dr J. J. A. McLaughlin (Haskins Laboratories, New York, personal communication) succeeded, however, with axenic cultures of another strain in 1954, but unfortunately was not in a position to pursue the matter. Dr McLaughlin's media contained, in addition to sources of water-soluble nutrients, such substances as soya meal, corpus luteum extract, cream, and beef serum in an attempt to meet the suspected fat requirement. These ingredients proved difficult to handle and unreliable in Dr McLaughlin's experience and, moreover, in my hands they entirely failed to support axenic growth. The first reliably successful axenic cultures at Millport were obtained in 1955 with a medium supplemented with 4 ml./l. of neutralized, strained but unfiltered, lemon juice. At a later date the juice was replaced by a carbon tetrachloride extract of the rind, which has the advantage of being composed entirely of fat-solubles. Isolation and identification of this fat-soluble 'lemon factor' is not completed, and will not be discussed further in this paper, which is concerned with water-soluble components of the medium.