UV-inducible DNA exchange in hyperthermophilic archaea mediated by type IV pili

Abstract

SummaryArchaea, like bacteria and eukaryotes, contain proteins involved in various mechanisms of DNA repair, highlighting the importance of these processes for all forms of life. Species of the order Sulfolobales of hyperthermophilic crenarchaeota are equipped with a strongly UV-inducible type IV pilus system that promotes cellular aggregation. Here we demonstrate by fluorescence in situ hybridization that cellular aggregates are formed based on a species-specific recognition process and that UV-induced cellular aggregation mediates chromosomal marker exchange with high frequency. Recombination rates exceeded those of uninduced cultures by up to three orders of magnitude. Knockout strains of Sulfolobus acidocaldarius incapable of pilus production could not selfaggregate, but were partners in mating experiments with wild-type strains indicating that one cellular partner can mediate the DNA transfer. Since pilus knockout strains showed decreased survival upon UV treatment, we conclude that the UV-inducible DNA transfer process and subsequent homologous recombination represents an important mechanism to maintain chromosome integrity in Sulfolobus. It might also contribute substantially to the frequent chromosomal DNA exchange and horizontal gene transfer in these archaea in their natural habitat.

Type IV Pilin Proteins: Versatile Molecular Modules

“…In many species, surface contact-or, perhaps, a local increase in viscosity or mechanical strain on membranes-leads to upregulation of pilin expression (43). In Haemophilus influenzae, alkaline pH is required for optimal pilus expression (33), while some archaea produce T4P in response to UV irradiation (7,147). For many pathogens, T4P are made only in response to growth under specific culture conditions or at specific temperatures and/or in response to host cell contact (102,254,274).…”

Homologous recombination in the archaeon Sulfolobus acidocaldarius: effects of DNA substrates and mechanistic implications

“…acidocaldarius expresses constitutively a conjugation system which requires type-IV pili (Ajon et al, 2011); this system provided the first quantitative genetic assay of HR in a Sulfolobus species (Grogan, 1996;Hansen et al, 2005). In order to analyse the pattern of markers transferred between strains by conjugation, we constructed parental strains containing multiple silent markers in their chromosomal pyrE gene.…”

A broadly applicable gene knockout system for the thermoacidophilic archaeon Sulfolobus islandicus based on simvastatin selection

“…For example, a primary system in Sulfolobus acidocaldarius utilizes uracil selection, in which spontaneous uracil auxotrophs in the pyrEF genes are selected for by resistance to the toxic compound 5-fluoroorotic acid (5-FOA). Transformants of these auxotrophs are then selected for by complementation through addition of a functional pyrEF cassette (Grogan, 2009 allelic replacement and markerless gene deletion, have been constructed in S. islandicus Rey15A and S. acidocaldarius (Ajon et al, 2011;Deng et al, 2009;Li et al, 2011;Sakofsky et al, 2011;Zhang et al, 2010).…”