A potential role for Streptococcus gordonii in haem acquisition by Porphyromonas gingivalis



Brown, JL
(2017) A potential role for Streptococcus gordonii in haem acquisition by Porphyromonas gingivalis. Master of Philosophy thesis, University of Liverpool.

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Abstract

Periodontitis (PD) is an inflammatory disease arising from the dental plaque bacterial insult upon the soft periodontal tissues, resulting in damage to the tooth supporting structures. Severe forms of the disease are the main cause of tooth loss in adults, which impacts on oral health and quality of life. As control of the growth of dental plaque is only partially successful in reducing the severity of PD, a better understanding of the biochemical interactions that exist between key pathogenic inhabitants within plaque may potentially lead to the development of novel therapeutic agents that could further aid in moderating PD. Porphyromonas gingivalis, a black-pigmenting species requiring haem for growth and virulence, is identified as one of the main protagonists in the onset and maintenance of PD. P. gingivalis co-aggregates with other auxiliary pathogens in dental plaque, including Streptococcus gordonii, a member of the viridans streptococci. This study primarily investigated a potential role for S. gordonii in one of the central mechanisms utilised by P. gingivalis to acquire haem from haemoglobin (Hb) i.e., via methaemoglobin (metHb) production. It was shown herein that hydrogen peroxide production by S. gordonii was responsible for mediating the formation of metHb; the Fe(III)haem-containing Hb species utilised by P. gingivalis for haem extraction. The haem from metHb generated by S. gordonii, was more easily extracted from the protein by the HmuY haemophore of P. gingivalis, than from metHb formed by auto-oxidation. Using circular dichroism spectroscopy, it was revealed that the increased rate of HmuY-Fe(III)haem complex formation likely arose as a result of subtle changes to the Hb structure following exposure to S. gordonii-generated hydrogen peroxide. Diabetes mellitus, which is characterised by hyperglycaemia and increased levels of glycated Hb, has long been considered a risk factor of PD. The numbers of Red complex microorganisms such as P. gingivalis and viridans streptococci are also increased in the subgingival plaque of diabetic individuals. Here, it was demonstrated that the HmuY haemophore of P. gingivalis extracted haem more readily from Hb glycated in vitro than from un-glycated Hb. Mass spectroscopy of the glycated Hb indicated that the protein contained multiple glycated lysine amino acids, including Lys-90(α) and Lys-95(β) located on the same F8 helix-loops as the proximal histidines which are involved in haem-globin binding. The experimental data obtained in this study has provided evidence for two potential mechanisms through which haem availability to P. gingivalis might be enhanced. The first involves formation of metHb via streptococcal production of hydrogen peroxide. The second mechanism points to Hb glycation, a process which enhances haem extraction by HmuY. These effects may contribute to haem acquisition by P. gingivalis and might account for the increased numbers in dental plaque of diabetics.

Item Type: Thesis (Master of Philosophy)
Divisions: Faculty of Health and Life Sciences > Faculty of Health and Life Sciences
Depositing User: Symplectic Admin
Date Deposited: 18 Sep 2017 13:40
Last Modified: 22 Sep 2021 07:11
DOI: 10.17638/03008059
Supervisors:
URI: https://livrepository.liverpool.ac.uk/id/eprint/3008059