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.

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The species richness of trees, shrubs and climbing plants was investigated in 41 sugi (Cryptomeria japonica D. Don) plantations of different stand age and area in southern Kyushu, southwestern Japan. Altogether 174 species were found, of which 145 infrequent species were selected for analysis. Two groups were extracted from the species list according to their occurrence in older (49 spp.) or younger (28 spp.) stands, the latter containing a higher percentage of climbing plants and species with wind-dispersed seeds. In contrast, the older stand group contained major tree components typical of seminatural, evergreen broadleaved forests in the region and was more heavily dependent on stand age, especially for species with gravity-and frugivoredispersed seeds, showing a gradual increase up to 60 years old. The species richness was less correlated with edge perimeter facing seminatural forests and the years after latest thinning. The juxtaposition of plantation compartments with stands of seminatural forest or other plantations, as well as the compartment's origin as former plantation site or a seminatural stand, had relatively little influence on species richness. However, topographic variation was important in determining the species composition, with valley stands having higher species richness and containing many plants typical of the regional seminatural forests. These results suggest that (1) the major trend of species richness is determined by the presence of old stand type species, (2) topographic variation of species richness remains even after establishment of plantations, and (3) the normal rotation period of sugi plantations (35-40 years) may therefore be too short to conserve the maximum potential species diversity within the working forest.

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