FINE-STRUCTURE EVIDENCE FOR CELL-MEMBRANE PARTITIONING OF THE NUCLEOID AND CYTOPLASM DURING BUD FORMATION IN HYPHOMONAS SPECIES

Hyphomonas spp, reproduce by budding from the tip of the prosthecum di stal to the main body of the reproductive cell; thus, the chromosome m ust travel through the prosthecum to enter the progeny, the swarm cell . When viewed by electron microscopy, negatively stained whole cells, ultrathin-sectioned cells, and freeze-etched and frozen hydrated cells all had marked swellings of the cytoplasmic membrane (CM) in the pros thecum which are termed pseudovesicles (PV), PV were separated by cons trictions in the contiguous CM. In replicating cells, PV housed riboso mes and DNA, which was identified by its fibrillar appearance and by l actoferrin-gold labeling, The micrographs also revealed that the CM bi furcates at the origin of the prosthecum so that one branch partitions the main body of the reproductive cell from the prosthecum and swarm cell, The results of this fine-structure analysis suggest models expla ining DNA segregation and the mal ked asymmetric polarity of the buddi ng reproductive cell.