Thermus thermophilus HB27 is an extremely thermophilic, halotolerant bacterium, which was originally isolated from a natural thermal environment in Japan. This organism has considerable biotechnological potential; many thermostable proteins isolated from members of the genus Thermus are indispensable in research and in industrial applications. We present here the complete genome sequence of T. thermophilus HB27, the first for the genus Thermus. The genome consists of a 1,894,877 base pair chromosome and a 232,605 base pair megaplasmid, designated pTT27. The 2,218 identified putative genes were compared to those of the closest relative sequenced so far, the mesophilic bacterium Deinococcus radiodurans. Both organisms share a similar set of proteins, although their genomes lack extensive synteny. Many new genes of potential interest for biotechnological applications were found in T. thermophilus HB27. Candidates include various proteases and key enzymes of other fundamental biological processes such as DNA replication, DNA repair and RNA maturation.

We recently identified a pilin-like competence factor, ComP, which is essential for natural transformation of the gram-negative soil bacterium Acinetobacter sp. strain BD413. Here we demonstrate that transcription and synthesis of the pilin-like competence factor ComP are maximal in the late stationary growth phase, whereas competence is induced immediately after inoculation of a stationary-phase culture into fresh medium. Western blot analyses revealed three forms of ComP, one with an apparent molecular mass of 15 kDa, which correlates with the molecular mass deduced from the DNA sequence, one 20-kDa form, which was found to be glycosylated, and one 23-kDa form. The glycosylation of ComP was not required for its function in DNA binding and uptake. The 20-kDa form was present in the cytoplasmic membrane, the periplasm, and the outer membrane, whereas the 23-kDa form was located in the outer membrane and might be due to a further modification. Immunological data suggest that ComP is not a subunit of the pilus structures. Possible functions of ComP in the DNA transformation machinery of Acinetobacter sp. strain BD413 are discussed.

Two structurally different appendages, thin and thick pili, are found in members of the genus Acinetobacter. The presence of pilus structures correlates with different phenotypes, such as adherence to surfaces, a trait not only observed in pathogenic Acinetobacter species, as well as motility. However, their distinct individual roles were unknown. To characterize the role of different pili in the physiology of Acinetobacter, we isolated the thin pili from the cell surface of Acinetobacter sp. strain BD413 (recently recognized as representative of Acinetobacter baylyi), a soil bacterium that rapidly takes up naked DNA from its environment. Electron microcopy revealed that the pilus has an external diameter of 2 to 3 nm for single filaments. The filaments are packed into right-handed bundles. The major protein constituting the pilus was purified, and the encoding gene, acuA, was cloned. AcuA was found to be weakly related to the structural subunit of F17 pili of Escherichia coli. Analyses of the acuA flanking DNA region led to the identification of three closely associated genes, acuD, acuC, and acuG, whose deduced proteins are similar to chaperone, usher, and adhesin of F17-related pili, respectively. Transcriptional analyses revealed that acuA expression is maximal in the late-stationary-growth phase. Mutation of acuA led to a loss of thin pili and concomitantly loss of adhesion to polystyrene and erythrocytes but not loss of competence. Therefore, thin pili of Acinetobacter sp. strain BD413 are suggested to be assembled by the chaperone/usher pathway and are involved in adherence to biotic and abiotic surfaces.

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