Surface characteristics of an adhesive thermophilic spore-forming Bacillus, isolated from milk powder : a thesis presented in partial fulfilment of the requirements for the degree of Doctor of Philosophy in Food Technology at Massey University, Palmerston North, New Zealand
Loading...
Date
2008
DOI
Open Access Location
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
Massey University
Rights
The Author
Abstract
The growth of thermophiles during the manufacture of milk powder leads to a
progressive increase in the number of thermophilic bacteria contaminating the final
product. The limited residence time of the milk in the plant during milk powder
manufacture and the concentration effect of converting milk into milk powder cannot
explain the number of thermophiles found in the final product. This suggests that
thermophiles are attaching to the large surface area of stainless steel found within a
milk powder plant and then growing and developing into biofilms, with individual
cells and/or biofilm fragments sloughing off into the product line and thus
contaminating the final product.
The aim of the present study was to investigate the attachment mechanisms that
enable the thermophile Anoxybacillus flavithermus (B 1 2) to attach to stainless steel
surfaces. Passing a B 1 2 culture through a column of stainless steel chips, collecting
the first cells to pass through, re-culturing and repeating the process six times,
resulted in the isolation of a mutant, labelled X7, with lO-fold reduced ability to
attach to stainless steel as well as a reduced ability to attach to plastic and glass.
A comparison of bacterial cell surface properties indicated that X7 was less
hydrophobic than its parental strain B 1 2 . Cell surface charge measurements also
suggest that X7 has less net negative surface charge. Disruption of extracellular
polysaccharides and DNA appeared to have no effect on the attachment process.
Removal of surface proteins caused a reduction in attachment of B 1 2 and X7 as well
as a reduction in surface hydrophobicity suggesting surface protein involvement in
both.
Analysis by two-dimensional gel electrophoresis of lysozyme/mutanolysin extracted
surface proteins revealed two proteins expressed at reduced levels in X 7 compared
with B 1 2 . One protein was identified by mass spectrometry as the cytoplasmic
enzyme Formate acetyltransferase. The role of Formate acetyltransferase and the
second unidentified protein on the attachment process of Anoxybacillus flavithermus
remains unclear.
Description
Keywords
Milk powder manufacture, Biofilm, Anoxybacillus flavithermus