Explosive cell lysis as a mechanism for the biogenesis of bacterial membrane vesicles and biofilms

Abstract

Many bacteria produce extracellular and surface-associated components such as membrane vesicles (MVs), extracellular DNA and moonlighting cytosolic proteins for which the biogenesis and export pathways are not fully understood. Here we show that the explosive cell lysis of a sub-population of cells accounts for the liberation of cytosolic content in Pseudomonas aeruginosa biofilms. Super-resolution microscopy reveals that explosive cell lysis also produces shattered membrane fragments that rapidly form MVs. A prophage endolysin encoded within the R- and F-pyocin gene cluster is essential for explosive cell lysis. Endolysin-deficient mutants are defective in MV production and biofilm development, consistent with a crucial role in the biogenesis of MVs and liberation of extracellular DNA and other biofilm matrix components. Our findings reveal that explosive cell lysis, mediated through the activity of a cryptic prophage endolysin, acts as a mechanism for the production of bacterial MVs.

Spatially dependent alkyl quinolone signaling responses to antibiotics in Pseudomonas aeruginosa swarms

“…In the Pseudomonas literature, AQs are generally presented to contain 7-Carbon (C7) side chains (HHQ, PQS, and HQNO), yet 9-Carbon (C9; NHQ, C9-PQS, and NQNO) and 11-Carbon (C11; UHQ, C11-PQS, and UQNO) side chain variants of these molecules are also common (16,17). The extracellular presence of PQS in P. aeruginosa communities is attributed to packaging and transport in outer membrane vesicles (OMVs) (28,29), yet cell lysis could also contribute to their release (30).…”

NontypeableHaemophilus influenzaereleases DNA and DNABII proteins via a T4SS-like complex and ComE of the type IV pilus machinery

“…Moreover and importantly, these giant rounded cells were observed for up to 6 h of culture and never lysed. Conversely, once formed, 86% of large rounded Pseudomonas cells survive for <60 s before lysing (36). The limited (if any) bacterial cell death and absence of explosive cell lysis under the culture conditions we tested suggested that the observed release of eDNA and associated DNABII proteins from NTHI very early in biofilm formation likely occurred via an alternative nonlytic mechanism.…”

“…For clarity, additional experiments were conducted with a viability stain to confirm this assertion. We next determined whether altruistic cell death by explosive cell lysis facilitated the observed deposition of DNA, as is described for Pseudomonas (36). Although a small number (<1 for every 1,000 cells) of NTHI did indeed form giant rounded cells similar in morphology to those described for Pseudomonas, these rounded cells did not form until much later in time [e.g., more than 3 h after inoculation compared with ≤1 h after incubation as reported for Pseudomonas (36)].…”

“…Staphylococcus aureus has been shown to undergo such an altruistic cell death (9). Recently, it was reported that a small proportion of Pseudomonas cells form very large rounded cells that then rapidly undergo explosive cell lysis and release their cellular contents, including DNA, into the extracellular environment (36). In addition, some species such as Neisseria have an active type IV secretion system that transports DNA from the cytoplasm to the extracellular space, presumably for gene transfer (35).…”

“…To date, the presence of bacterial eDNA within biofilms has been attributed to release via various mechanisms, including cell lysis (autolysis or phagemediated) (12,32,33), or active secretion through type IV secretion systems (T4SSs) (34,35). Recently, DNA has been shown to be released from Pseudomonas aeruginosa by explosive cell lysis that is predicated on the formation of giant rounded cells that ultimately rapidly lyse, thereby releasing cell contents into the environment (36). However, a mechanism for the specific release of DNABII proteins into the extracellular space has been heretofore unknown.…”