The biochemical and biophysical characterisation of protein antibiotics targeting Pectobacterium spp. and Streptococcus agalactiae

Thompson, Catriona M.A. (2019) The biochemical and biophysical characterisation of protein antibiotics targeting Pectobacterium spp. and Streptococcus agalactiae. PhD thesis, University of Glasgow.

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Abstract

Food security is the idea by which a population has enough food to sustain itself without famine. A large number of factors can influence the stability of food production, including diseases caused by microorganisms. Pectobacterium spp. is one of the leading causes of soft rot disease, resulting in crop losses both pre- and post-harvest.
Bacteriocins are potent narrow spectrum protein antibiotics which target closely related bacteria to the producing strain. Ferredoxin-containing bacteriocins produced by and targeted towards Pectobacterium species have both a different domain organisation and uptake mechanism to all known Gram-negative bacteriocins. This work has shown that pectocins are able to pass through the outer membrane of Pectobacterium spp. by parasitising the ferredoxin uptake receptor, FusA. This uptake requires the pectocins to be flexible in order to pass through the lumen of the barrel and enter the periplasm. This work has shown an interaction between FusB and pectocin M1, suggesting a novel mechanism of uptake.
Streptococcus agalactiae is the causative agent of disease in a wide range of hosts, ranging from human neonates to farmed Tilapia. S. agalactiae infection has a detrimental effect on the dairy industry each year as it is the leading cause of mastitis in cattle. As well as this, the prevalence of S. agalactiae in farmed fish has resulted in large numbers of infected fish and subsequently the infection of consumers.
Bacteriocins produced by Gram-positive bacteria are often small modified peptides which target the peptidoglycan layer or cytoplasmic membrane of the target cell. However, a small number of protein bacteriocins produced by Gram-positive bacteria have been discovered, with the best characterised of these being lysostaphin. It has been shown that bacteriocins similar to lysostaphin are also produced by other Gram-positive bacteria, such as zoocin A produced by Streptococcus zooepidemicus. Prior to this work a novel protein bacteriocin produced by and targeted towards S. agalactiae, named agalacticin A, was discovered. It was predicted that this bacteriocin was similar in structure and function to zoocin A. This work has gone some way to structurally characterising agalacticin A, showing a two-domain structure joined by a flexible linker region allowing for the two domains to move independently. As well as this it has shown the importance of the histidine residues at the predicted active site confirming the similarities between agalacticin A and zoocin A. Together this work has gone some way to showing the potential of agalacticin A as a novel therapeutic.
Altogether this work has characterised three novel bacteriocins active against pathogenic bacteria to gain a better understanding of their structure, mechanism of action and uptake.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Pectobacterium, Streptococcus, bacteriocins, uptake of bacteriocins, FusA, FusB, pectocins, zoocin, agalacticin.
Subjects: Q Science > QH Natural history > QH301 Biology
Q Science > QH Natural history > QH345 Biochemistry
Q Science > QR Microbiology
Colleges/Schools: College of Medical Veterinary and Life Sciences > Institute of Infection Immunity and Inflammation > Bacteriology
Funder's Name: Biotechnology and Biological Sciences Research Council (BBSRC), Biotechnology and Biological Sciences Research Council (BBSRC)
Supervisor's Name: Walker, Professor Daniel and Byron, Professor Olwyn
Date of Award: 2019
Depositing User: Dr Catriona M A Thompson
Unique ID: glathesis:2019-41021
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 25 Feb 2019 11:59
Last Modified: 25 Feb 2019 12:01
URI: http://theses.gla.ac.uk/id/eprint/41021

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