Characterization of the holdfast region of wild-type cells and holdfast mutants of Asticcacaulis biprosthecum

Mutants of Asticcacaulis biprosthecum lacking the ability to attach to various surfaces were selected by serial transfer in liquid media containing cheesecloth, to which wild-type cells attach but holdfast mutants do not. Congo red, incorporated into solid media, distinguishes between colonies of wild-type cells and those of holdfast mutants. Holdfast mutants were characterized and compared to wild-type cells according to their ability to swim, to attach to each other or to wild-type cells, for the presence on the cells of polar surface structures (holdfast, flagella, pili), and for sensitivity to phages. All holdfast mutants produced flagella, even though some mutants were nonmotile. Eighteen holdfast mutants fell into two groups: those apparently defective only in holdfast function and those defective in additional structures localized at the holdfast pole of the cell. None of these holdfast mutants was defective in prosthecal development. All holdfast mutants are capable of forming rosettes with wild-type cells, even though they are incapable of initiating attachment on their own, suggesting polymeric bridging as a likely mechanism for attachment.Abbreviation PYE peptone-yeast extract