<P> Some pili, called type IV pili (T4P), generate motile forces . The external ends of the pili adhere to a solid substrate, either the surface to which the bacterium is attached or to other bacteria . Then, when the pili contract, they pull the bacterium forward like a grappling hook . Movement produced by type IV pili is typically jerky, so it is called twitching motility, as opposed to other forms of bacterial motility such as that produced by flagella . However, some bacteria, for example Myxococcus xanthus, exhibit gliding motility . Bacterial type IV pili are similar in structure to the component flagellins of archaella (archaeal flagella). </P> <P> Genetic transformation is the process by which a recipient bacterial cell takes up DNA from a neighboring cell and integrates this DNA into its genome by homologous recombination . In Neisseria meningitidis (also called meningococcus), DNA transformation requires the presence of short DNA uptake sequences (DUSs) which are 9 - 10 monomers residing in coding regions of the donor DNA . Specific recognition of DUSs is mediated by a type IV pilin . Menningococcal type IV pili bind DNA through the minor pilin ComP via an electropositive stripe that is predicted to be exposed on the filament's surface . ComP displays an exquisite binding preference for selective DUSs . The distribution of DUSs within the N. meningitides genome favors certain genes, suggesting that there is a bias for genes involved in genomic maintenance and repair . </P> <P> To initiate formation of a biofilm, fimbriae must attach bacteria to host surfaces for colonization during infection . A fimbria is a short pilus that is used to attach the bacterium to a surface . They are sometimes called "attachment pili". Fimbriae are either located at the poles of a cell or are evenly spread over its entire surface . Mutant bacteria that lack fimbriae cannot adhere to their usual target surfaces, and thus cannot cause diseases . </P> <P> Some fimbriae can contain lectins . The lectins are necessary to adhere to target cells because they can recognize oligosaccharide units on the surface of these target cells . Other fimbriae bind to components of the extracellular matrix . Fimbriae found in Gram - negative have the pilin subunits covalently linked . </P>

What does pili do in a prokaryotic cell