Biogenesis and function of type IV pili in pseudomonas species

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Pseudomonas, 2006, 4 pp. 139 - 188
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© 2006 Springer. All rights reserved. Type IV pili or fimbriae are non-flagellar, filamentous surface appendages that are associated with a number of biological activities in bacteria. These processes include a form of surface translocation termed twitching motility; bacteriophage sensitivity; attachment to biotic (bacteria, plant, animal) and abiotic surfaces; biofilm development; and the uptake of naked DNA by natural transformation. Many of these biological functions are reliant on the ability of these structures to extend and retract. Type IV pili/fimbriae are found throughout the eubacteria. They are produced by many species of Gram-negative bacteria and have been most extensively studied in Pseudomonas aeruginosa, Neisseria gonorrhoeae, N. meningitidis, Dichelobacter nodosus, Moraxella bovis, Myxococcus xanthus, and Synechocystis species PCC 6803, enteropathogenic Eschericia coli (EPEC) and Vibrio cholerae98,99,143 Type IV pili/fimbriae are also produced by some Gram-positive bacteria including Ruminococcus albus163,168 and probably Streptococcus sanguis100 though evidence for the latter awaits confirmation via molecular analyses. The nomenclature "type IV" is derived from the classification scheme outlined by Ottowin 1975 inwhich he grouped non-flagellar filamentous structures into six types based largely on morphological characteristics156 Interestingly, throughout this nomenclature system Ottow reserved the use of the term pili to specifically refer to conjugative sex pili and used the term "fimbriae" for all other non-flagellar filamentous surface organelles. The term "fimbriae" was also favored by other investigators72,82 however, historically, the terms "pili" and "fimbriae" have been used interchangeably. In reference to the non-flagellar filamentous structures thatwere classified by Ottowas "Group IV," the terminology "type IV pili" and its abbreviation "tfp" have become very much the vogue in recent years and will be adopted in this review. As defined by Ottow (1975) type IV pili are "⋯ flexible, rod-like, polarly inserted fimbriae." The tfp of P. aeruginosa were amongst the first of this class described in bacteria20,21,25,82,104,226 P. aeruginosa tfp have a diameter of 5-6 nm25,50,77,226 and a hollow core of 1.2 nm.77 Due to their retractile nature, the length of these structures varies significantly, but on average are about 1-4 μm in length22,24,27 although they can range in length up to 10 μm25,226 A number of studies have examined tfp production by P. aeruginosa under different culture conditions and have shown that P. aeruginosa tfp are produced throughout plate culture22,119,209,226 in logarithmic broth culture with gentle agitation22,25,226 and by stationary phase bacteria when cultured without aeration or with only gentle agitation22,119,209,226 whereas vigorously shaken stationary phase P. aeruginosa cultures do not produce detectable tfp22,119,209,226 Type IV pili have also been identified in other Pseudomonas species including P. syringae180-183 P. stutzeri84,98 and P. fluorescens138 (see Section 2.6). Historically, however, P. aeruginosa has served as one of the primary model organisms for the investigation of tfp and its associated functions in bacteria. It is for this reason that this chapter will largely focus on the tfp of P. aeruginosa. This chapter will review the current state of knowledge relating to the structure, biogenesis, and function of the tfp of the genus Pseudomonas and will also highlight advances made in the study of these structures in other type IV piliated bacteria.
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