PATTERN OF SHEATH SYNTHESIS IN SPHAEROTILUS NATANS.

Romano, Antonio H. (University of Cincinnati, Cincinnati, Ohio), and Dorothy J. Geason. Pattern of sheath synthesis in Sphaerotilus natans. J. Bacteriol. 88:1145-1150. 1964.-Formation of the characteristic sheath of Sphaerotilus natans was followed by immunofluorescence. Fluorescent antisheath antibody was obtained by injecting rabbits with purified sheath material from S. natans, fractionating the serum with ammonium sulfate, and conjugating the globulin fraction with fluorescein isothiocyanate. To follow sheath formation, S. natans was grown on slides immersed in Stokes' medium at 28 C for 9 hr, and was reacted with labeled antibody. The slide cultures were then washed to remove unbound antibody, and were incubated further in fresh medium. Samples were removed at intervals and examined by fluorescence microscopy. Old portions of the sheath remained discretely labeled with no diminution in intensity of fluorescence, whereas non-fluorescent new sheath material appeared at the ends of the filaments. These results indicate that sheath synthesis does not take place by intussusception or diffuse intercalation, but by linear extension of pre-existing sheath. This interpretation was confirmed by a reverse procedure, whereby old sheath was reacted with unlabeled antibody, and new sheath was identified by addition of labeled antibody after further incubation. In this procedure, fluorescence was most intense at the growing tips of the filaments.