Optimised bacterial production and characterisation of natural antimicrobial peptides with potential application in agriculture
Date
2016-03
Authors
Journal Title
Journal ISSN
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Publisher
Stellenbosch : Stellenbosch University
Abstract
ENGLISH ABSTRACT : The loss incurred due to microbial spoilage is a great concern to the agricultural and food
industries. Microbial pathogens have typically been controlled through the use of chemical
control agents and antibiotics. However, combination of emerging microbial resistance
together with consumer opposition and regulation toward these chemical agents has instigated
the need for so called green-biocides which have a reduced ecological impact together with
lower potential for resistance development. The tyrocidines and their analogues, cyclic
decapeptides produced by the soil bacterium Bacillus aneurinolyticus, show potential to serve
as green-biocides. Potent antimicrobial activity toward bacterial and fungal pathogens which
affect both the food and agricultural industries is achieved by different cyclodecapeptide
analogues.
The objective of this study was the development and evaluation of the future potential of the
cyclodecapeptides produced by B. aneurinolyticus to serve as green-biocides. In this thesis an
overview is given in Chapter 1 of the challenges facing agricultural production due to
microbial spoilage and resistance, as well as the potential of antimicrobial peptides,
specifically the tyrocidines and analogues to address this problem. The optimal conditions
allowing for future large scale production of target-specific subsets of these
cyclodecapeptides and economical downstream purification of the peptide mixtures and
single peptides is covered in Chapters 2-4. The produced cyclodecapeptide
mixtures/formulations were investigated to elucidate some parameters which may allow for
optimisation to target different agricultural and/or food related pathogens/problem organisms
(Chapters 5 and 6). Initial formulation parameters were evaluated together with the relative
safety of their application within an agricultural setting by determining their in vivo toxicity
toward honey bees (Chapter 7). A Summary of the findings in each of the different chapters is
presented together with proposed future work (Chapter 8). The experimental chapters of this
thesis were written as independent units so as to enable future publication. In some chapters
repetitions were unavoidable, every attempt was made to keep this to a minimum.
The first goal of this study was the increased natural production of these cyclodecapeptides to
enabling their tailored application to target different pathogens in an agricultural
environment. In order to achieve the goal of this study the following objectives were set:
Manipulation of the natural cyclodecapeptide profile of B. aneurinolyticus to produce
defined peptide subsets and single peptides. (Chapter 2).
Construction of a computational model of cyclodecapeptide production by
B. aneurinolyticus (Chapter 3).
Optimise production and purification methodology of the tyrocidines and their
analogues for future large scale production (Chapter 4).
The second goal was to characterise the peptides in order to facilitate formulation of the
peptides for in vivo applications. In order to achieve the goal of this study the following
objectives were set:
Investigate the structure and oligomerisation relationships of the major
cyclodecapeptide analogues produced in the different subsets (Chapter 5).
Correlation of the oligomerisation characteristics of co-produced cyclodecapeptides
with their antimicrobial activity toward two representative target organisms (Chapter
6).
Formulation of the natural cyclodecapeptide extracts and investigation of their in vivo
toxicity toward honey bees as representative non-target species (Chapter 7).
Description
Thesis (PhD)--Stellenbosch University, 2016
Keywords
Tyrocidine, Bacterial production, UCTD, Bacteria -- Pathogens, Antimicrobial peptides (AMPs), Green biocides