Clarification of large-volume bacterial cultures using a centrifuge-free protocol

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Aims: To provide a reliable, reproducible and centrifuge-free filtration protocol for clarification of large volumes of bacterial cultures. Methods and Results: Four experiments were designed to compare different techniques enabling clarification of Escherichia coli cultures using as a benchmark the concentration and quality of bacterial outer membrane vesicles (OMVs). The experiments were designed to examine the performance of different extraction methods on large volume (≥1 L) filtrations of bacterial culture media. Performance parameters included filtration flow rates, sterility testing and characterization of the filtrates by: (i) SDS-PAGE, (ii) cryogenic transmission electron microscopy, (iii) nanoparticle tracking analysis and (iv) Qubit protein quantification. The experiments revealed that: (i) addition of the filter aid Diatomaceous Earth to the bacterial cultures improved filtration flow rates significantly and eliminated the need for centrifugation prior to filtration; (ii) sterile filtration was successful as no bacterial passage was identified through the membrane filter; (iii) centrifuge-free filtrates contained an increased amount of OMVs compared to centrifuged filtrates. Conclusions: In comparison to conventional centrifuge-based protocols, the clarification method presented has universal applicability for a broad range of microbial extraction procedures, regardless of the volume of culture harvested. Moreover, the decreased amount of OMVs presented in the filtrates following centrifugation step provides an additional argument in favour of a centrifuge-free approach. Significance and Impact of the Study: Sterile filtration is a universal method for the clarification of bacterial cultures. Common challenges related to filtration include filter clogging and long processing times, due to limited centrifugation capacity, which can affect product quality. The proposed protocol is likely to ensure a highly effective filtration process and could be a novel approach in improving the filtrate products without the need of centrifugation.

OriginalsprogEngelsk
TidsskriftJournal of Applied Microbiology
Vol/bind133
Udgave nummer2
Sider (fra-til)870-882
ISSN1364-5072
DOI
StatusUdgivet - 2022

Bibliografisk note

Funding Information:
This work was supported by the Department of Veterinary and Animal Sciences, University of Copenhagen, Denmark. Funding information

Funding Information:
We are grateful to the Department of Veterinary and Animal Sciences (University of Copenhagen) for the financial support provided to this project. We thank Sartorius for their cooperation and insight in the development of the system proposed. Among the team at Sartorius, special thanks go to John Cashman, Andreas Pickl, Samantha Ottolangui and Klaus Schoene. We acknowledge the Core Facility for Integrated Microscopy (Faculty of Health and Medical Sciences, University of Copenhagen) for the TEM imaging described in this investigation. Special thanks go to Klaus Qvortrup and Michael Johnson for their invaluable technical expertise. We are also immensely grateful to Peter Lindberg Nejsum and Anders Toftegaard Boysen for their support with OMV quantification by NTA.

Publisher Copyright:
© 2022 The Authors. Journal of Applied Microbiology published by John Wiley & Sons Ltd on behalf of Society for Applied Microbiology.

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