Direct visualization of sequence-specific DNA binding by gonococcal type IV pili

Type IV pili of Enterobacteriaceae species

Type IV pili (T4Ps) are surface filaments widely distributed among bacteria and archaea. T4Ps are involved in many cellular functions and contribute to virulence in some species of bacteria. Due to the diversity of T4Ps, different properties have been observed for homologous proteins that make up T4Ps in various organisms. In this review, we highlight the essential components of T4Ps, their functions, and similarities to related systems. We emphasize the unique T4Ps of enteric pathogens within the Enterobacteriaceae family, which includes pathogenic strains of Escherichia coli and Salmonella. These include the bundle-forming pilus (BFP) of enteropathogenic E. coli (EPEC), longus (Lng) and colonization factor III (CFA/III) of enterotoxigenic E. coli (ETEC), T4P of Salmonella enterica serovar Typhi, Colonization Factor Citrobacter (CFC) of Citrobacter rodentium, T4P of Yersinia pseudotuberculosis, a ubiquitous T4P that was characterized in enterohemorrhagic E. coli (EHEC), and the R64 plasmid thin pilus. Finally, we highlight areas for further study.

Uptake of environmental DNA in Bacillus subtilis occurs all over the cell surface through a dynamic pilus structure

At the transition to stationary phase, a subpopulation of Bacillus subtilis cells can enter the developmental state of competence, where DNA is taken up through the cell envelope, and is processed to single stranded DNA, which is incorporated into the genome if sufficient homology between sequences exists. We show here that the initial step of transport across the cell wall occurs via a true pilus structure, with an average length of about 500 nm, which assembles at various places on the cell surface. Once assembled, the pilus remains at one position and can be retracted in a time frame of seconds. The major pilin, ComGC, was studied at a single molecule level in live cells. ComGC was found in two distinct populations, one that would correspond to ComGC freely diffusing throughout the cell membrane, and one that is relatively stationary, likely reflecting pilus-incorporated molecules. The ratio of 65% diffusing and 35% stationary ComGC molecules changed towards more stationary molecules upon addition of external DNA, while the number of pili in the population did not strongly increase. These findings suggest that the pilus assembles stochastically, but engages more pilin monomers from the membrane fraction in the presence of transport substrate. Our data support a model in which transport of environmental DNA occurs through the entire cell surface by a dynamic pilus, mediating efficient uptake through the cell wall into the periplasm, where DNA diffuses to a cell pole containing the localized transport machinery mediating passage into the cytosol.

Multisite transformation in Neisseria gonorrhoeae: insights on transformations mechanisms and new genetic modification protocols

Natural transformation, or the uptake of naked DNA from the external milieu by bacteria, holds a unique place in the history of biology. This is both the beginning of the realization of the correct chemical nature of genes and the first technical step to the molecular biology revolution that sees us today able to modify genomes almost at will. Yet the mechanistic understanding of bacterial transformation still presents many blind spots and many bacterial systems lag behind power horse model systems like Escherichia coli in terms of ease of genetic modification. Using Neisseria gonorrhoeae as a model system and using transformation with multiple DNA molecules, we tackle in this paper both some aspects of the mechanistic nature of bacterial transformation and the presentation of new molecular biology techniques for this organism. We show that similarly to what has been demonstrated in other naturally competent bacteria, Neisseria gonorrhoeae can incorporate, at the same time, different DNA molecules modifying DNA at different loci within its genome. In particular, co-transformation of a DNA molecule bearing an antibiotic selection cassette and another non-selected DNA piece can lead to the integration of both molecules in the genome while selecting only through the selective cassette at percentages above 70%. We also show that successive selections with two selection markers at the same genetic locus can drastically reduce the number of genetic markers needed to do multisite genetic modifications in Neisseria gonorrhoeae. Despite public health interest heightened with the recent rise in antibiotic resistance, the causative agent of gonorrhea still does not possess a plethora of molecular techniques. This paper will extend the techniques available to the Neisseria community while providing some insights into the mechanisms behind bacterial transformation in Neisseria gonorrhoeae. We are providing a suite of new techniques to quickly obtain modifications of genes and genomes in the Neisserial naturally competent bacteria.