Enterococcus adhesin PrgB facilitates type IV secretion by condensation of extracellular DNA

Abstract

Conjugative type IV secretion systems (T4SSs) are multi-protein complexes in Gram-negative and Gram-positive (G+) bacteria, responsible for spreading antibiotic resistances and virulence factors among different species. Compared to Gram-negative bacteria, which establish close contacts for conjugative transfer via sex pili, G+ T4SSs are suggested to employ surface adhesins instead. One example is pCF10, an enterococcal conjugative sex-pheromone responsive plasmid with a narrow host range, thus disseminating genetic information only among closely related species. This MicroCommentary is dedicated to the crystal structure of the pCF10-encoded adhesion domain of PrgB presented by Schmitt et al. The authors show in their work that this adhesion domain is responsible for biofilm formation, tight binding and condensation of extracellular DNA (eDNA) and conjugative transfer of pCF10. A sophisticated two-step mechanism for highly efficient conjugative transfer is postulated, including the formation of PrgB-mediated long-range intercellular contacts by binding and establishment of shorter-range contacts via condensation of eDNA. PrgB binding to lipoteichoic acid on the recipient cell surface stabilizes junctions between the mating partners. The major findings by Schmitt et al. will be brought into a broader context and potential medical applications targeting eDNA as essential component in biofilm formation and conjugation will be discussed.

Antibacterial and antibiofilm activities of thyme oil against foodborne multiple antibiotics-resistant Enterococcus faecalis

“…The biofilm-associated Ebp pili of E. faecalis play an important role in bacterial adherence to different surfaces ( La Rosa et al., 2016 ; Afonina et al., 2018 ). Besides Ebp pili, type IV Pili are also important in cell motility, adherence, and biofilm formation of E. faecalis ( Kohler et al., 2018 ; Schmitt et al., 2018 ). The effects of thyme oil on E. faecalis motility were analyzed, and the diameters of bacterial halos corresponding to swimming and swarming motilities of bacterial cells treated with 64, 128, and 256 μg/mL thyme oil significantly decreased compared with those of the control ( P < 0.05) ( Figure 2 ).…”

Polymer Adhesin Domains in Gram-Positive Cell Surface Proteins

“…Expression of PrgB leads to cellular clumping (Dunny et al, 1978;Bhatty et al, 2015), which is dependent on the polymer adhesin domain binding to eDNA (Kohler et al, 2018;Schmitt et al, 2018). Surprisingly, this interaction does not take place at the conserved ridge with the cation binding site (Figure 2).…”

“…Streptococcus mutans Sommer et al, 1987;Oho et al, 1998;Troffer-Charlier et al, 2002;Sato et al, 2002a;Nakano et al, 2006;Busscher et al, 2007;Larson et al, 2010;Heim et al, Kreft et al, 1992;Bensing and Dunny, 1993;Rakita et al, 1999;Vanek, 1999;Hirt et al, 2000;Wells et al, 2000;Waters and Dunny, 2001;Isenmann et al, 2002;Waters et al, 2003Waters et al, , 2004Chuang et al, 2009;Chuang-Smith et al, 2010;Bhatty et al, 2015;Kohler et al, 2018;Schmitt et al, 2018 IV Aggregation substance (AS) prgB, asa1, asp1, asc10…”

“…As we will discuss in this review, the conserved adhesion module consistently adheres to various types of polymers associated with the extracellular matrix, such as collagen (Love et al, 1997;Holmes et al, 1998;Heddle et al, 2003), extracellular DNA (eDNA; Kohler et al, 2018;Schmitt et al, 2018), lipoteichoic acid (LTA; Waters et al, 2004;Schmitt et al, 2018), or different types of glucans (Sato et al, 2002b;Tamura et al, 2014;Mieher et al, 2018). Therefore, we will throughout this review refer to this adhesion module as the polymer adhesin domain.…”

Structural and biochemical analysis of OrfG: the VirB8-like component of the integrative and conjugative element ICESt3 from Streptococcus thermophilus

“…Based on the structural and genetic information gathered from previous studies, it is assumed that the Conj-T4SSs from Gram-positive bacteria are essentially composed of subunits related to components recovered in Gram-negative T4SS. These ones comprise (i) VirB4 and VirD4-like energetic components, (ii) VirB3-, VirB6-and VirB8-like membrane subunits that assemble in the cytoplasmic membrane to form the membrane platform, (iii) VirB1-like transglycosylase and (iv) surface adhesins crucial in cell-to-cell contact or cells aggregation [12][13][14][15][16][17]. Finally, Conj-T4SSs from Gram-positive bacteria also comprise a set of accessory proteins with undefined functions [18].…”