Horizontal transference of S-layer genes within Thermus thermophilus

Abstract

The S-layers of Thermus thermophilus HB27 and T. thermophilus HB8 are composed of protein units of 95 kDa (P95) and 100 kDa (P100), respectively. We have selected S-layer deletion mutants from both strains by complete replacement of the slpA gene. Mutants of the two strains showed similar defects in growth and morphology and overproduced an external cell envelope inside of which cells remained after division. However, the nature of this external layer is strain specific, being easily stained and regular in the HB8⌬slpA derivative and amorphous and poorly stained in the HB27⌬slpA strain. The addition of chromosomic DNA from T. thermophilus HB8 to growing cultures of T. thermophilus HB27⌬slpA led to the selection of a new strain, HB27C8, which expressed a functional S-layer composed of the P100 protein. Conversely, the addition of chromosomic DNA from T. thermophilus HB27 to growing cultures of T. thermophilus HB8⌬slpA allowed the isolation of strain HB8C27, which expressed a functional S-layer composed of the P95 protein. The driving force which selected the transference of the S-layer genes in these experiments was the difference in growth rates, one of the main factors leading to selection in natural environments.In many mesophilic bacteria, the presence of crystalline surface layers (S-layers) seems to be a strain-specific character, whose loss upon optimal growth conditions results in S-layer mutants that do not present any apparent phenotypic defect (12, 21). By contrast, most thermophiles, especially those belonging to the oldest phylogenetic branches (31), contain Slayer as an almost universal character, thus suggesting for these structures important roles in cell viability or membrane integrity at high temperatures. In fact, the presence of S-layer in evolutionarily old thermophilic bacteria and their structural simplicity led to the suggestion of an ancient evolutionary origin for such structures (26).As S-layers completely surround the cells, their building units constitute one of the major membrane proteins. Accordingly, synthesis of the S-layer is a metabolically expensive process which could be selected during evolution only as a result of the existence of strong selective pressures. However, little is known about such selective pressures, and even less is known about the role(s) that S-layers could play in mesophilic or thermophilic natural environments.Like any cell surface components, S-layers should be subjected to strong selective pressures, the most important of which could be the presence of hydrolytic enzymes (essentially proteases) and bacteriophages (as binding sites). Such selective pressures could be the factors responsible for the sequence divergence of the S-layer genes (21). In fact, it has been not possible to obtain clear phylogenetic relationships between S-layer genes, even from related organisms. In addition, the possibility exists that horizontal transference of S-layer genes within genetically related strains contributed to the present sequence divergence, in a way similar to th...

A conserved motif in S-layer proteins is involved in peptidoglycan binding in Thermus thermophilus

“…The rabbit polyclonal antiserum revealed the presence of proteins immunologically related to SlpA in all of the strains assayed. From these, the 95-, 100-, and 110-kDa proteins detected in T. thermophilus HB27, Thermus sp., and D. radiodurans, respectively, were in accordance with the sizes of their respective S-layer proteins (1,4,13). The smaller bands detected in these isolates most probably corresponded to proteolytic fragments of the full-size S-layer protein (1,13).…”

“…Deinococcus radiodurans (29), Thermus aquaticus YT1 (ATCC 25105), and T. thermophilus HB27 were generously given by W. Baumeister, M. Bothe, and Y. Koyama, respectively. The construction of the strain T. thermophilus HB27C8 has been described previously (13) T. thermophilus strains were grown at 70ЊC under strong aeration in a rich medium containing 8 g of Trypticase (BBL, Cockeysville, Md. ), 4 g of yeast extract (Oxoid, Hampshire, England), and 3 g of NaCl per liter of tap water, adjusted to pH 7.5.…”

“…For plasmid transformation, essentially the method described by Koyama et al was used (15). T. thermophilus HB27C8 was grown at 70ЊC in a transformation medium as described elsewhere (13).…”

“…As the outermost envelope, the functions of S-layers are related to their interaction with the specific environment in which these organisms grow. However, their constant presence in bacteria belonging to the oldest phylogenetic groups and the severe defects shown by S-layer-defective mutants in these groups (13,17) suggest that primitive S-layers could have played a role essentially related to the maintenance of the cell morphology and envelope integrity (2,22).…”

The surface (S)-layer gene cspB of Corynebacterium glutamicum is transcriptionally activated by a LuxR-type regulator and located on a 6 kb genomic island absent from the type strain ATCC 13032

“…The S-layer mRNAs of Bacillus anthracis, Lactobacillus brevis and Thermus thermophilus contain 59 untranslated regions of up to 300 bp in length that might be involved in stabilization of the transcript (Mignot et al, 2002;Vidgren et al, 1992). For instance, the C-terminal part of the S-layer protein SlpA of T. thermophilus binds to the 59 leader region of the slpA mRNA, providing a clue to the mechanism of post-transcriptional autoregulation during the expression of slpA (Fernandez-Herrero et al, 1997). The highly stable S-layer mRNAs of Caulobacter crescentus and L. brevis possess long half-lives of 10-15 min and 32 min, respectively (Fisher et al, 1988;Kahala et al, 1997).…”