title: TgaA, a VirB1-like component belonging to a putative type IV secretion system of Bifidobacterium bifidum MIMBb75.
abstract: Bifidobacterium bifidum MIMBb75 is a human intestinal isolate demonstrated to be interactive with the host and efficacious as a probiotic. However, the molecular biology of this microorganism is yet largely unknown. For this reason, we undertook whole-genome sequencing of B. bifidum MIMBb75 to identify potential genetic factors that would explain the metabolic and probiotic attributes of this bacterium. Comparative genomic analysis revealed a 45-kb chromosomal region that comprises 19 putative genes coding for a potential type IV secretion system (T4SS). Thus, we undertook the initial characterization of this genetic region by studying the putative virB1-like gene, named tgaA. Gene tgaA encodes a peptidoglycan lytic enzyme containing two active domains: lytic murein transglycosylase (LT, cd00254.3) and cysteine- and histidine-dependent amidohydrolase/peptidase (CHAP, pfam05257.4). By means of several in vitro assays, we experimentally confirmed that protein TgaA, consistent with its computationally assigned role, has peptidoglycan lytic activity, which is principally associated to the LT domain. Furthermore, immunofluorescence and immunogold labeling showed that the protein TgaA is abundantly expressed on the cell surface of B. bifidum MIMBb75. According to the literature, the T4SSs, which have not been characterized before in bifidobacteria, can have important implications for bacterial cell-to-cell communication as well as cross talk with host cells, justifying the interest for further studies aimed at the investigation of this genetic region.
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy simone.guglielmetti@unimi.it.
authors.forename: Simone
authors.initials: S
authors.lastname: Guglielmetti
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Balzaretti
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Valentina
authors.initials: V
authors.lastname: Taverniti
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Matteo
authors.initials: M
authors.lastname: Miriani
authors.affiliation: Laboratory of Probiogenomics, Department of Life Sciences, University of Parma, Parma, Italy.
authors.forename: Christian
authors.initials: C
authors.lastname: Milani
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Alessio
authors.initials: A
authors.lastname: Scarafoni
authors.affiliation: IRCCS Policlinico San Matteo, Pavia, Italy.
authors.forename: Silvia
authors.initials: S
authors.lastname: Corona
authors.affiliation: Department of Chemistry and Bioengineering, Tampere University of Technology, Tampere, Finland.
authors.forename: Alessandro
authors.initials: A
authors.lastname: Ciranna
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Arioli
authors.affiliation: Department of Chemistry and Bioengineering, Tampere University of Technology, Tampere, Finland.
authors.forename: Ville
authors.initials: V
authors.lastname: Santala
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Stefania
authors.initials: S
authors.lastname: Iametti
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Francesco
authors.initials: F
authors.lastname: Bonomi
authors.affiliation: Laboratory of Probiogenomics, Department of Life Sciences, University of Parma, Parma, Italy.
authors.forename: Marco
authors.initials: M
authors.lastname: Ventura
authors.affiliation: Department of Food Environmental and Nutritional Sciences, Università degli Studi di Milano, Milan, Italy.
authors.forename: Diego
authors.initials: D
authors.lastname: Mora
authors.affiliation: Department of Chemistry and Bioengineering, Tampere University of Technology, Tampere, Finland.
authors.forename: Matti
authors.initials: M
authors.lastname: Karp
mesh_terms: D058947:Bacterial Secretion Systems / Q000235:genetics*; D001644:Bifidobacterium / Q000235:genetics* / Q000378:metabolism*; D004269:DNA, Bacterial / Q000737:chemistry* / Q000235:genetics*; D005798:Genes, Bacterial; D016680:Genome, Bacterial; D006868:Hydrolysis; D008969:Molecular Sequence Data; D010457:Peptidoglycan / Q000378:metabolism; D017422:Sequence Analysis, DNA
chemical_list: D058947:Bacterial Secretion Systems; D004269:DNA, Bacterial; D010457:Peptidoglycan