Pigmentation phenotype instability in Myxococcus xanthusl ROBERT P. BUR CHARD^ A N D ANNC. BURCHARD Depcrrtt?l~tltof Blologicnl Scietlces, ( J t ~ r r ~ e r ~r!fr tM ) ~o r y l n t ~ dBaltit?~oreCorrt~ty,Ctrtotl.s\~ille.M D , U . S . A . 21228

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J . H. PARISH Depnrttnc.t~toJ'Biochetnistry, Ut~ir,ersity~ ~ ' L c L vLreds / s , LS2 9LS. Ut~iteclKitrgdot?~

Accepted August 31, 1977 BURCHARD. R . P.. A. C. BURCHARD. and J. H . PARISH.1977. Pigmentation phenotype instability in My.rococcrrs srrt~tl~ris. Can. J . Microbiol. 23: 1657- 1662. Cells of M.vsococcrrs,rnt~tl~~~s FB2 produce tan o r yellow colonies. Subcultures of tan colonies yielded tan and yellow colonies and s~rbculturesof most yellow colonies yielded only yellow colonies. Strain FB2 variants in which the color type is more stable were obtained. Yellow cells were distinguishable from tan by the presence of a pigment(s) with an absorption maximum at 379 nrn. Fluctuation Test experiments and the presence of this pigment(s) in liquid cultures of FB2 indicated that tan phenotype cells spontaneously became or segregated yellow cells in liquid culture. The frequency of appearance of yellow cells was increased in low density cultures (