Functional analysis of PilT from the toxic cyanobacterium Microcystis aeruginosa PCC 7806.
The evolution of the microcystin toxin gene cluster in phylogenetically distant cyanobacteria has been attributed to recombination, inactivation, and deletion events, although gene transfer may also be involved. Since the microcystin-producing Microcystis aeruginosa PCC 7806 is naturally transformable, we have initiated the characterization of its type IV pilus system, involved in DNA uptake in many bacteria, to provide a physiological focus for the influence of gene transfer in microcystin evolution. The type IV pilus genes pilA, pilB, pilC, and pilT were shown to be expressed in M. aeruginosa PCC 7806. The purified PilT protein yielded a maximal ATPase activity of 37.5 +/- 1.8 nmol P(i) min(-1) mg protein(-1), with a requirement for Mg(2+). Heterologous expression indicated that it could complement the pilT mutant of Pseudomonas aeruginosa, but not that of the cyanobacterium Synechocystis sp. strain PCC 6803, which was unexpected. Differences in two critical residues between the M. aeruginosa PCC 7806 PilT (7806 PilT) and the Synechocystis sp. strain PCC 6803 PilT proteins affected their theoretical structural models, which may explain the nonfunctionality of 7806 PilT in its cyanobacterial counterpart. Screening of the pilT gene in toxic and nontoxic strains of Microcystis was also performed.
Nakasugi
Kenlee
K
School of Biotechnology and Biomolecular Sciences, The University of New South Wales, Sydney, NSW 2052, Australia.
Alexova
Ralitza
R
Svenson
Charles J
CJ
Neilan
Brett A
BA
D000251:Adenosine Triphosphatases / Q000235:genetics / Q000502:physiology*; D001426:Bacterial Proteins / Q000235:genetics / Q000502:physiology*; D001483:Base Sequence; D010861:Fimbriae, Bacterial / Q000235:genetics; D046931:Microcystis / Q000502:physiology*; D008958:Models, Molecular; D020409:Molecular Motor Proteins / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D011550:Pseudomonas aeruginosa / Q000235:genetics; D046939:Synechocystis / Q000235:genetics
D001426:Bacterial Proteins; D020409:Molecular Motor Proteins; D000251:Adenosine Triphosphatases