Abstract
In bacterial contact-dependent growth inhibition (CDI) systems, CdiA proteins are exported to the outer membrane by cognate CdiB proteins. CdiA binds to receptors on susceptible bacteria and subsequently delivers its C-terminal toxin domain (CdiA-CT) into neighbouring target cells. Whereas self bacteria produce CdiI antitoxins, non-self bacteria lack antitoxins and are therefore inhibited in their growth by CdiA. In silico surveys of pathogenic Acinetobacter genomes have enabled us to identify >40 different CDI systems, which we sorted into two distinct groups. Type-II CdiAs are giant proteins (3711 to 5733 residues) with long arrays of 20-mer repeats. Type-I CdiAs are smaller (1900–2400 residues), lack repeats and feature central heterogeneity (HET) regions, that vary in size and sequence and can be exchanged between CdiA proteins. HET regions in most type-I proteins confer the ability to adopt a coiled-coil conformation. CdiA-CT and pretoxin modules differ significantly between type-I and type-II CdiAs. Moreover, type-II genes only have remnants of genes in their 3′ end regions that have been displaced by the insertion of novel cdi sequences. Type-I and type-II CDI systems are equally abundant in A. baumannii, whereas A. pittii and A. nosocomialis predominantly feature type-I and type-II systems, respectively.
Highlights
In bacterial contact-dependent growth inhibition (CDI) systems, CdiA proteins are exported to the outer membrane by cognate CdiB proteins
Acinetobacter proteins annotated as haemagglutinins using the KEGG (Kyoto Encyclopedia of Genes and Genomes) database were used as queries to search for CdiA-encoding genes in ACB complex genomes deposited in GenBank
For each Acinetobacter strain, the sequence type (ST), which was determined with the Acinetobacter Pasteur Multi Locus Sequence Typing (MLST) system[27], is provided
Summary
In bacterial contact-dependent growth inhibition (CDI) systems, CdiA proteins are exported to the outer membrane by cognate CdiB proteins. Prokaryotes have developed multiple systems to secrete proteins outside the cell to promote bacterial virulence, facilitate attachment to eukaryotic cells, scavenge iron and other resources in the environment, and damage neighbouring cells Based on their structure and function, secretion apparatuses are generally divided into six different classes. Extensive research has identified and characterized a subset of TPS systems involved in the secretion of toxic proteins One of these systems is the contact-dependent growth inhibition (CDI) system, where CdiA proteins are exported onto the outer membrane by cognate transporter CdiB proteins. Contact-dependent inhibition is mediated by type VI secretion systems (T6SSs), which are protein needles assembled onto bacterial outer membranes that pierce target cells to deliver toxic proteins[11]. ADP1 A.sp.21871 781407 UH19608 A.sp.FDAARGOS_131 A.sp.OIFC021 M3AC9-7 NIPH 67 TG21145 TG27387 1035119 A.sp. 1542444 PHEA-2 Naval-72 GK2 118362 1267820 OIFC111 232184 299505 1598530 NIPH 615 219_ABAU 99063 NIPH 146
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