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Evidence for Proline Utilization by Oral Bacterial Biofilms Grown in Saliva

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Original languageEnglish
Article number619968
JournalFrontiers in microbiology
Published20 Jan 2021

Bibliographical note

Funding Information: This work was funded by a BBSRC Lido-associated Ph.D. studentship for LC in association with Colgate-Palmolive, USA. Funding Information: The authors would like to acknowledge the support and expertise of Dr. Andrew Atkinson and Dr. Adrien Le Guennec at the NMR Centre, King's College London, UK. Funding. This work was funded by a BBSRC Lido-associated Ph.D. studentship for LC in association with Colgate-Palmolive, USA. Publisher Copyright: © Copyright © 2021 Cleaver, Moazzez and Carpenter. Copyright: Copyright 2021 Elsevier B.V., All rights reserved.

King's Authors


Within the mouth bacteria are starved of saccharides as their main nutrient source between meals and it is unclear what drives their metabolism. Previously oral in vitro biofilms grown in saliva have shown proteolytic degradation of salivary proteins and increased extracellular proline. Although arginine and glucose have been shown before to have an effect on oral biofilm growth and activity, there is limited evidence for proline. Nuclear magnetic resonance (NMR) spectroscopy was used to identify extracellular metabolites produced by bacteria in oral biofilms grown on hydroxyapatite discs. Biofilms were inoculated with stimulated whole mouth saliva and then grown for 7 days using sterilized stimulated whole mouth saliva supplemented with proline, arginine or glucose as a growth-medium. Overall proline had a beneficial effect on biofilm growth—with significantly fewer dead bacteria present by biomass and surface area of the biofilms (p < 0.05). Where arginine and glucose significantly increased and decreased pH, respectively, the pH of proline supplemented biofilms remained neutral at pH 7.3–7.5. SDS-polyacrylamide gel electrophoresis of the spent saliva from proline and arginine supplemented biofilms showed inhibition of salivary protein degradation of immature biofilms. NMR analysis of the spent saliva revealed that proline supplemented biofilms were metabolically similar to unsupplemented biofilms, but these biofilms actively metabolized proline to 5-aminopentanoate, butyrate and propionate, and actively utilized glycine. This study shows that in a nutrient limited environment, proline has a beneficial effect on in vitro oral biofilms grown from a saliva inoculum.

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