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.

Bacterial biofilms are composed of aggregates of cells encased within a matrix of extracellular polymeric substances (EPS). One key EPS component is extracellular DNA (eDNA), which acts as a ‘glue’, facilitating cell–cell and cell–substratum interactions. We have previously demonstrated that eDNA is produced in Pseudomonas aeruginosa biofilms via explosive cell lysis. This phenomenon involves a subset of the bacterial population explosively lysing, due to peptidoglycan degradation by the endolysin Lys. Here we demonstrate that in P. aeruginosa three holins, AlpB, CidA and Hol, are involved in Lys-mediated eDNA release within both submerged (hydrated) and interstitial (actively expanding) biofilms, albeit to different extents, depending upon the type of biofilm and the stage of biofilm development. We also demonstrate that eDNA release events determine the sites at which cells begin to cluster to initiate microcolony formation during the early stages of submerged biofilm development. Furthermore, our results show that sustained release of eDNA is required for cell cluster consolidation and subsequent microcolony development in submerged biofilms. Overall, this study adds to our understanding of how eDNA release is controlled temporally and spatially within P. aeruginosa biofilms.

Background: To estimate how much additional funding is needed for poverty-related and neglected disease (PRND) product development and to target new resources effectively, policymakers need updated information on the development pipeline and estimated costs to fill pipeline gaps. Methods: We previously conducted a pipeline review to identify candidates for 35 neglected diseases as of August 31, 2017 (“2017 pipeline”). We used the Portfolio-to-Impact (P2I) tool to estimate costs to move these candidates through the pipeline, likely launches, and additional costs to develop “missing products.” We repeated this analysis, reviewing the pipeline to August 31, 2019 to get a time trend. We made a direct comparison based on the same 35 diseases (“2019 direct comparison pipeline”), then a comparison based on an expanded list of 45 diseases (“2019 complete pipeline”). Results: In the 2017 pipeline, 538 product candidates met inclusion criteria for input into the model; it would cost $16.3 billion (B) to move these through the pipeline, yielding 128 launches. In the 2019 direct comparison pipeline, we identified 690 candidates, an increase of 152 candidates from 2017; the largest increase was for Ebola.  The direct comparison 2019 pipeline yields 196 launches, costing $19.9B. In the 2019 complete pipeline, there were 754 candidates, an increase of 216 candidates from 2017, of which 152 reflected pipeline changes and 64 reflected changes in scope. The complete pipeline 2019 yields 207 launches, costing $21.0B. There would still be 16 “missing products” based on the complete 2019 pipeline; it would cost $5.5B-$14.2B (depending on product complexity) to develop these products. Conclusion: The PRNDs product development pipeline has grown by over a quarter in two years. The number of expected new product launches based on the 2019 pipeline increased by half compared to 2017; the cost of advancing the pipeline increased by a quarter.

Bacterial biofilms are comprised of aggregates of cells encased within a matrix of extracellular polymeric substances (EPS). One key EPS component is extracellular DNA (eDNA), which acts as a "glue", facilitating cell-cell and cell-substratum interactions. We have previously demonstrated that eDNA is produced in Pseudomonas aeruginosa biofilms via explosive cell lysis. This phenomenon involves a subset of the bacterial population explosively lysing, due to peptidoglycan degradation by the endolysin Lys. Here we demonstrate that in P. aeruginosa three holins, AlpB, CidA and Hol, are involved in Lys-mediated eDNA release within both submerged (hydrated) and interstitial (actively expanding) biofilms, albeit to different extents, depending upon the type of biofilm and the stage of biofilm development. We also demonstrate that eDNA release events determine the sites at which cells begin to cluster to initiate microcolony formation during the early stages of submerged biofilm development. Furthermore, our results show that sustained release of eDNA is required for cell cluster consolidation and subsequent microcolony development in submerged biofilms. Overall, this study adds to our understanding of how eDNA release is controlled temporally and spatially within P. aeruginosa biofilms.