Factors affecting filamentous growth of Sphaerotilus natans.

Filamentous growth in cultures of Sphaerotilus natans can be measured and compared with total growth by a standardized procedure of winding filaments around an inoculating needle. Filaments and residual growth are then separately washed on Millipore filters, dried, and weighed. This method has been used to study changes in the growth habit of S. natans elicited by changes in the concentration of nutrients in the medium. The concentration of peptone, in a medium containing a sugar, phosphate buffer, and inorganic salts, has a much greater effect on the proportion of filamentous growth than does the nature or concentration of the carbon source or the concentration of phosphate buffer. Filament formation is significantly inhibited by concentrations of peptone greater than 0.25%; further increases in peptone concentration stimulate the production of large amounts of capsular material. Increasing the concentration of phosphate buffer to 0.05 M almost completely inhibits growth of S. natans.