Adaptation in micro-organisms : third symposium of the Society for General Microbiology held at the Royal Institution, London, April 1953 / [edited by R. Davies and E.F. Gale].

  • Society for General Microbiology. Symposium (3rd : 1953 : London, England)
Date:
1953
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Licence: Attribution-NonCommercial-NoDerivatives 4.0 International (CC BY-NC-ND 4.0)

Credit: Adaptation in micro-organisms : third symposium of the Society for General Microbiology held at the Royal Institution, London, April 1953 / [edited by R. Davies and E.F. Gale]. Source: Wellcome Collection.

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    ADAPTATIONS IN PARAMECIUM 299 subsequent growth in culture medium (lacking serum), and completely replaced the D antigens some two to four fissions later, depending on the severity of the initial treatment. Exposure to homologous antiserum did not therefore directly change the antigens, but started some change in the paramecia which resulted in the occurrence of a transformation during subsequent growth. The change from type D to type В was shown by Sonneborn to be permanent, provided certain cultural conditions (one fission per day at 27°) were maintained. Under these conditions the two different types could be preserved, in parallel cultures, indefinitely, irrespective of the occurrence of autogamy. Under certain other conditions a reversal from В to D could be obtained (though indirectly, i.e. by passing through a third antigenic type). Serum-induced transformation from type D to type В in stock 51 could be brought about with great regularity, as indicated above. Nevertheless, treatment of other antigenic types (in stock 51, or in any other stock) by homologous antisera may completely fail to produce any transformations; frequently animals recovering from such treatment are of the same antigenic type as before, and continue to be so. More¬ over, it sometimes even happens that serum treatment has a stabilizing effect, in that serum-treated animals are less likely to change than untreated ones (Skaar, unpublished). Whether an antigenic change will follow from serum treatment depends on many factors, both external and internal, and no general predictions are possible. It has been found with all stocks of P. aurelia which have been adequately studied that a whole series of mutually exclusive antigens may occur in different animals of the same stock, i.e. of the same genotype. For example, Sonneborn (1950ûf) found as many as eight distinct types in stock 51, and more could undoubtedly be found by further study. Changes of antigenic type may be induced, without the use of serum, in the following ways (amongst others): (1) by varying the temperature; (2) by varying the quantity of food; (3) by varying the salinity of the medium, and (4) by exposure to trypsin or chymotrypsin. [(1), (2) and (4) see Sonneborn (1950è); (3) Beale, unpublished.] Some of these treatments have been found to yield very regular results. Thus in variety 1 of P. aurelia the S type was formed at low temperatures (10-18°), the G type at medium temperatures (18-25°), and the D type at high temperatures (29-35°). The change from one type to another was abrupt, occurring in the time of two fissions, but many fissions might occur between change of temperature and consequent change of antigenic type. In general, the more extreme changes of