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Analysis of Pseudomonas aeruginosa biofilm membrane vesicles supports multiple mechanisms of biogenesis.

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PubMed ID: 30763382

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Cooke AC, Nello AV, Ernst RK, Schertzer JW

PLoS One. 2019. doi: 10.1371/journal.pone.0212275

COMMENT: Bacterial Outer Membrane Vesicles (OMVs) naturally exist in Gram-negative bacteria. They play a critical role in the bacteria-bacteria and bateria-host interactions and have been implicated in biofilm development. To assess the OMV structure, biogenesis and function, vesicles isolated from planktonic cultures has been extensively used. In this work, the authors try to understand how OMVs are produced and used by bacteria living as a biofilm. 

OBJECTIVE: 

With this work, we investigate the physical size, function and mechanisms of biogenesis of OMVs in agar plate model biofilms and compare our findings to what has been reported for bacteria growing planktonically or in other biofilm models.

MAIN RESULTS:

In PA14 (...) the planktonic OMVs were smaller than the biofilm OMVs. (...) PAO1 OMVs were larger than PA14 OMVs under all conditions. 

The smaller PA14 OMVs were more effective at inhibiting growth of S. epidermidis than the larger PAO1 OMVs. Looking only at PA14 OMVs, the smaller planktonic OMVs were more effective than the larger biofilm OMVs.

(...) the size distribution of pqsA mutant vesicles was much wider than wild type vesicles (...) When pqsA was reintroduced to the mutant strain, we found that the OMV distribution matched the distribution of the wild type.

As the biofilm develops, the OMV size distribution shifts to more heavily represent larger vesicles. 

CONCLUSION:

OMV size characteristics of P. aeruginosa OMVs are dependent on the strain producing the OMVs, and the environment in which the bacteria are producing the OMVs. 

Differences in OMV predatory ability vary more between strains than between modes of growth for an individual strain. 

We demonstrated that the small molecule PQS plays an important role in biofilm OMV biogenesis in our system, as it also does in planktonic cultures.

Multiple mechanisms for MV biogenesis exist and may come to prominence under differing environmental conditions.

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Raquel Ruiz-Arroyo