- Email: [email protected]
Multicellular growth of bacteria
COMMENT Horizons Natural genetic engineers
I
ntegrons are genetic elements that can acquire open reading frames (gene cassettes) and convert them to functional genes. Over 40 cassettes have been found so far, all of which encode antibiotic resistance. Mazel et al. have recently identified a Vibrio cholerae integron that clusters genes for pathogenicity. The insertion of a gene cassette takes place by sitespecific recombination, catalysed by integron-encoded integrase, between a circularized cassette and the recipient integron. The V. cholerae intI4 integron gene encodes a previously unknown integrase that is associated with a ‘gene-VCR (V. cholerae repeat sequence)’ organization that is
Hiding Fas
C
ytotoxic T lymphocytes (CTLs) typically kill virus-infected cells by two main pathways: perforin-mediated lysis or Fasmediated lysis. A novel mechanism for escaping one of these antiviral pathways has been described by Tollefson et al. They have observed that cells infected with adenovirus have greatly decreased levels of the Fas receptor on their surface and that an adenovirus protein, RID (‘receptor internalization and degradation’), mediates the internalization of Fas molecules. Fas is then destroyed within lysosomal compartments, an event that is not observed in uninfected cells. Although RID also mediates the internali-
Multicellular growth of bacteria
P
seudomonas aeruginosa is an opportunistic pathogen that can colonize catheters and the lungs of cystic fibrosis patients. It is protected from antimicrobial agents by the ability to form biofilms. LasI encodes the production of the quorum sensing signal N-(3-oxododecanoyl)-L-homoserine lactone. Davies et al. now report that a lasI mutant of P. aeruginosa is defective in normal biofilm formation. This
similar to that of the well-characterized antibiotic-resistance integrons. The similarity has been confirmed by IntI1-mediated recombination of a gene-VCR cassette into a class 1 integron. VCR cassettes are found in several Vibrio species, suggesting that this mechanism pre-dated the antibiotic era. Therefore, the integrons might be generalized gene acquisition systems that capture different biochemical functions and not only antibiotic resistance. Mazel, D. et al. (1998) A distinctive class of integron in the Vibrio cholerae genome, Science 280, 605–608
Ivan Matic e-mail: [email protected]
zation/destruction of epidermal growth factor receptor, it does not affect two other surface antigens: the transferrin receptor or major histocompatibility complex (MHC) class I molecules. The results of this study indicate that, by removing Fas from the surface of the infected cell, adenovirus may more effectively evade Fas-mediated lysis and thus prolong its survival in the infected host. Tollefson, A.E. et al. (1998) Forced degradation of Fas inhibits apoptosis in adenovirus-infected cells, Nature 392, 726–730
Mark Slifka e-mail: [email protected]
mutant formed a biofilm that was only 20% as thick as the one formed by wild-type P. aeruginosa and was sensitive to the detergent sodium dodecyl sulfate. Clearly, these results have important medical implications and point towards new strategies for the control of biofilm-forming pathogens. However, they also provide an example of an increasing trend pointing to complex multicellular traits in bacteria. The idea of multicellularity among ‘simple’
Microbial genomics Yersinia pestis genome Funded by Beowulf Genomics (http: //www.beowulf.org.uk), a recent initiative of the Wellcome Trust, The Sanger Centre has begun work on the 4.38-Mb genome sequence of the plague pathogen, Yersinia pestis (http://www.sanger. ac.uk/Projects/Y_pestis/). Research is being carried out on strain CO-92 biovar Orientalis in collaboration with researchers at St Bartholomew’s and the Royal London School of Medicine and Dentistry, London, UK (http://www. medmicro.mds.qmw.ac.uk/yersinia), Imperial College, London (http:// www.bc.ic.ac.uk/research/dougan/ dougan_intro.html) and the Defence Evaluation Research Agency, Porton Down, UK (http://www.dra.hmg.gb/dera.htm). In an unrelated initiative, researchers at the Lawrence Livermore National Laboratory have recently completed the entire sequences of the three Y. pestis plasmids: the 9.6-kb pesticin plasmid (pPCP1), the 70-kb calcium-dependence plasmid (pCD1) and the 100-kb murine toxin plasmid (pMT1) (http://www. ncbi.nlm.nih.gov/htbinpost/Entrez/query?uid=2996286, 2996222,2996216&form=6&db=n). The plasmid sequences confirm the presence of many known virulence genes (e.g. the Yops and associated type III secretion system genes), while analyses of potential coding sequences have revealed interesting motifs in some hypothetical proteins; for example, an RGD (Arg–Gly–Asp) cell attachment sequence and an ATPbinding motif (P-loop). Mark Pallen e-mail: [email protected]
bacteria has been around for many years and met with early skepticism. It is now clear that a bacterial colony holds many exciting mysteries worthy of exploration. Davies, D.G. et al. (1998) The involvement of cell-to-cell signals in the development of a bacterial biofilm, Science 280, 295–298
Gary Stacey e-mail: [email protected]
Copyright © 1998 Elsevier Science Ltd. All rights reserved. 0966 842X/98/$19.00
TRENDS
IN
MICROBIOLOGY
261
VOL. 6 NO. 7 JULY 1998
I
ntegrons are genetic elements that can acquire open reading frames (gene cassettes) and convert them to functional genes. Over 40 cassettes have been found so far, all of which encode antibiotic resistance. Mazel et al. have recently identified a Vibrio cholerae integron that clusters genes for pathogenicity. The insertion of a gene cassette takes place by sitespecific recombination, catalysed by integron-encoded integrase, between a circularized cassette and the recipient integron. The V. cholerae intI4 integron gene encodes a previously unknown integrase that is associated with a ‘gene-VCR (V. cholerae repeat sequence)’ organization that is
Hiding Fas
C
ytotoxic T lymphocytes (CTLs) typically kill virus-infected cells by two main pathways: perforin-mediated lysis or Fasmediated lysis. A novel mechanism for escaping one of these antiviral pathways has been described by Tollefson et al. They have observed that cells infected with adenovirus have greatly decreased levels of the Fas receptor on their surface and that an adenovirus protein, RID (‘receptor internalization and degradation’), mediates the internalization of Fas molecules. Fas is then destroyed within lysosomal compartments, an event that is not observed in uninfected cells. Although RID also mediates the internali-
Multicellular growth of bacteria
P
seudomonas aeruginosa is an opportunistic pathogen that can colonize catheters and the lungs of cystic fibrosis patients. It is protected from antimicrobial agents by the ability to form biofilms. LasI encodes the production of the quorum sensing signal N-(3-oxododecanoyl)-L-homoserine lactone. Davies et al. now report that a lasI mutant of P. aeruginosa is defective in normal biofilm formation. This
similar to that of the well-characterized antibiotic-resistance integrons. The similarity has been confirmed by IntI1-mediated recombination of a gene-VCR cassette into a class 1 integron. VCR cassettes are found in several Vibrio species, suggesting that this mechanism pre-dated the antibiotic era. Therefore, the integrons might be generalized gene acquisition systems that capture different biochemical functions and not only antibiotic resistance. Mazel, D. et al. (1998) A distinctive class of integron in the Vibrio cholerae genome, Science 280, 605–608
Ivan Matic e-mail: [email protected]
zation/destruction of epidermal growth factor receptor, it does not affect two other surface antigens: the transferrin receptor or major histocompatibility complex (MHC) class I molecules. The results of this study indicate that, by removing Fas from the surface of the infected cell, adenovirus may more effectively evade Fas-mediated lysis and thus prolong its survival in the infected host. Tollefson, A.E. et al. (1998) Forced degradation of Fas inhibits apoptosis in adenovirus-infected cells, Nature 392, 726–730
Mark Slifka e-mail: [email protected]
mutant formed a biofilm that was only 20% as thick as the one formed by wild-type P. aeruginosa and was sensitive to the detergent sodium dodecyl sulfate. Clearly, these results have important medical implications and point towards new strategies for the control of biofilm-forming pathogens. However, they also provide an example of an increasing trend pointing to complex multicellular traits in bacteria. The idea of multicellularity among ‘simple’
Microbial genomics Yersinia pestis genome Funded by Beowulf Genomics (http: //www.beowulf.org.uk), a recent initiative of the Wellcome Trust, The Sanger Centre has begun work on the 4.38-Mb genome sequence of the plague pathogen, Yersinia pestis (http://www.sanger. ac.uk/Projects/Y_pestis/). Research is being carried out on strain CO-92 biovar Orientalis in collaboration with researchers at St Bartholomew’s and the Royal London School of Medicine and Dentistry, London, UK (http://www. medmicro.mds.qmw.ac.uk/yersinia), Imperial College, London (http:// www.bc.ic.ac.uk/research/dougan/ dougan_intro.html) and the Defence Evaluation Research Agency, Porton Down, UK (http://www.dra.hmg.gb/dera.htm). In an unrelated initiative, researchers at the Lawrence Livermore National Laboratory have recently completed the entire sequences of the three Y. pestis plasmids: the 9.6-kb pesticin plasmid (pPCP1), the 70-kb calcium-dependence plasmid (pCD1) and the 100-kb murine toxin plasmid (pMT1) (http://www. ncbi.nlm.nih.gov/htbinpost/Entrez/query?uid=2996286, 2996222,2996216&form=6&db=n). The plasmid sequences confirm the presence of many known virulence genes (e.g. the Yops and associated type III secretion system genes), while analyses of potential coding sequences have revealed interesting motifs in some hypothetical proteins; for example, an RGD (Arg–Gly–Asp) cell attachment sequence and an ATPbinding motif (P-loop). Mark Pallen e-mail: [email protected]
bacteria has been around for many years and met with early skepticism. It is now clear that a bacterial colony holds many exciting mysteries worthy of exploration. Davies, D.G. et al. (1998) The involvement of cell-to-cell signals in the development of a bacterial biofilm, Science 280, 295–298
Gary Stacey e-mail: [email protected]
Copyright © 1998 Elsevier Science Ltd. All rights reserved. 0966 842X/98/$19.00
TRENDS
IN
MICROBIOLOGY
261
VOL. 6 NO. 7 JULY 1998