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The Sensitivity of Brewing Micro-Organisms to Silver by Patrick Strecker School of Biosciences the University of Nottingham

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The Sensitivity of Brewing Micro-Organisms to Silver by Patrick Strecker School of Biosciences the University of Nottingham The Sensitivity of Brewing Micro-organisms to Silver By Patrick Strecker School of Biosciences The University of Nottingham Thesis submitted to the University of Nottingham for the degree of Doctor of Philosophy Supervised by Prof. K.A. Smart, Prof. C. Dodd, Dr. J. Hobman, Dr. T. Phister and Dr. F. Bealin-Kelly July 2015 Abstract With respect to microbiological food safety, beer is thought to be very safe. This is due to the inability of pathogenic organisms to survive in the harsh environment that beer presents, due to low pH, alcohol content and hop acids. However, there are some organisms which have adapted to brewery conditions and can cause off-flavours, hazes or low ethanol yield. The effects of spoilage and subsequent product recall can result in massive economic losses for brewing companies affected. Silver nano-particle coatings for pipes and vessels have been suggested as a means of eliminating or reducing contaminants in the brewery. In this study the sensitivity of several brewery contaminants to silver has been investigated. Pichia membranaefaciens, Brettanomyces anomalous, Candida krusei, Hansenula saturnus, Kloeckera apiculata, Rhodotorula mucilaginosa, Saccharomyces ellipsoids var. diastaticus, Lactobacillus brevis, Pediococcus damnosus, were all tested against a range of silver nitrate concentrations (0-1 mM) in YPD, wort and beer. It was found that sensitivity to silver varied between organisms, but no tolerance exceeded 0.55 mM. It was also found that for the majority of organisms, tolerance to silver decreased under simulated brewery conditions i.e. wort, beer and microaerophillic conditions. In the investigation of potential silver tolerance mechanisms, gene microarrays of Saccharomyces ellipsoids var. diastaticus in wort and beer in the presence and absence of silver found that genes most up-regulated during silver stress were those with transmembrane transporter functions. Silver tolerance testing with gene deletion strains of selected potential silver tolerance genes demonstrated reduced silver tolerance for the deletion strains of the HIS1, COX17 and CUP1 genes. All three of these have known functions in copper tolerance. The data collected in this study would suggest that silver (particularily in nanoparticle form) is an effective means of microbial brewery contamination control especially under brewery conditions. However, further study is needed into the effect of silver antimicrobial surfaces on brewery microbial contaminants, silver concentrations needed in antimicrobial surfaces and silver leaching etc. Acknowledgements I would like to thank my supervisors Prof. K. Smart, Prof. C. Dodd, Dr. J. Hobman, Dr. T. Phister and Dr. F. Bealin-Kelly, as well as the Bioenergy and Brewing Science group for their help, guidance and support throughout my project. I would also like to thank the BBSRC and SABMiller for their funding of this project. Abbreviations AAB – Acetic acid Bacteria ABC – ATP-binding cassette ABV – Alcohol by volume ADP – Adenosine diphosphate ANOVA – Analysis of variance ATNCs – Apparent total N-nitroso compounds ATP – Adenosine triphosphate Bp – Base pair CCP – Critical control points cDNA – Complementary deoxyribonucleic acid Cfu – Colony forming units CIP – Cleaning in place cm – Centimeter COP – Cleaning out of place DEFT – Direct epifluorescent filter technique DEPEC – Diethylpyrocarbonate Dm – Decimetre DMS – Dimethyl sulphide DMSO – Dimethyl sulfoxide DNA – Deoxyribonucleic acid EBC – European brewery convention EDTA – Ethylenediaminetetraacetic acid ELISA – Enzyme linked immunosorbent assay g – Gram g – Gravity HACCP – Hazard analysis critical control points ICP-MS – Inductively coupled plasma mass spectrometry ITS – Internally transcribed spacer region Kb - Kilobase KEGG – Kyoto encyclopedia of genes and genomes L – Liter LAB – Lactic acid bacteria LB – Lysogeny broth (medium) M – Mol MALDI-TOF – Matrix assisted laser desorption ionization - time of flight mg – Milligram MIC – Minimum inhibitory concentration Min – Minutes ml – Milliliter mm – Millimeter mM – Millimolar mmol – Millimols Mol – Molar mRNA – Messenger ribonucleic acid MRS – de Man, Rogosa and Sharpe (medium) mtDNA – Mitochondrial deoxyribonucleic acid MYPG – Malt yeast peptone glucose (medium) NAD – Nicotinamide adenine dinucleotide (oxidised) NADH – Nicotinamide adenine dinucleotide (reduced) NADP – Nicotinamide adenine dinucleotide phosphate (oxidised) NADPH – Nicotinamide adenine dinucleotide phosphate (reduced) NASC – Nottingham arabidopsis stock centre NB – Nutrient broth (medium) NBB – Nocive brewers bacteria (medium) NCBI – National center for biotechnology information ng – Nanogram nm – Nanometer OD – Optical Density ORF – Open reading frame PAA – Peracetic acid PCR – Polymerase chain reaction POF – Phenolic off-flavour ppm – Parts per million psi – Pounds per square inch QAS – Quaternary ammonium salts rDNA – Ribosomal deoxyribonucleic acid RFLP – Restriction fragment length polymorphism RNA – Ribonucleic acid RO – Reverse osmosis (water) ROS – Reactive oxygen species rpm – Revolutions per minute rRNA – Ribosomal ribonucleic acid SDS – Sodium dodecyl sulfate Sec – Seconds SGD – Saccharomyces genome data base TCA – Tricarboxylic acid TEM – Transmission electron microscopy UBA – Universal beer agar v/v – Volume/volume WLN – Wallerstein laboratory nutrient w/v – Weight/volume YPD - Yeast extract peptone dextrose (medium) µg – Microgram µm – Micrometer µM – Micromolar µl – Microlitre Table of Contents Chapter 1 Literature Review .................................................................................................... 1 1.1 Introduction ................................................................................................................... 1 1.2 The Brewing Process ...................................................................................................... 2 1.3 Brewery Contaminants and Where They Occur ............................................................. 7 1.3.1 Microbial Contamination of Barley and Malt .......................................................... 8 1.3.2 Microbial Contamination of Mashing and Wort preparation .................................. 9 1.3.3 Microbial Contamination during Fermentation ....................................................... 9 1.3.4 Microbial Contamination during Conditioning and Packaging .............................. 10 1.3.5 Microbial Contamination of Final Product ............................................................ 12 1.3.6 Major Contaminant Organisms of the Brewing Industry ....................................... 14 1.3.7 Known Physiology of the Test Strains ........................................................................ 16 1.3.7.1 Bacteria .............................................................................................................. 16 1.3.7.1.1 Lactobacillus brevis ......................................................................................... 16 1.3.7.1.2 Pediococcus damnosus .................................................................................... 17 1.3.7.1.3 Shimwellia pseudoproteus ............................................................................... 18 1.3.7.1.4 Bacillus coagulans ........................................................................................... 19 1.3.7.1.5 Pantoea agglomerans ..................................................................................... 19 1.3.7.1.6 Gluconobacter oxydans and Acetobacter aceti ............................................... 20 1.3.7.2 Yeasts ................................................................................................................. 21 1.3.7.2.1 Pichia membranaefaciens ............................................................................... 21 1.3.7.2.2 Brettanomyces anomalus ................................................................................ 21 1.3.7.2.3 Candida krusei ................................................................................................. 22 1.3.7.2.4 Hansenula saturnus (Williopsis saturnus) ........................................................ 22 1.3.7.2.5 Kloeckera apiculata ......................................................................................... 23 1.3.7.2.6 Rhodotorula mucilaginosa............................................................................... 23 1.3.7.2.7 Saccharomyces ellipsoides var. diastaticus ...................................................... 24 1.4 Current Means of Detection and Identification of Microbial Contamination ............... 24 1.4.1 Classical Microbiology ........................................................................................... 25 1.4.2 Optical Microscopic Techniques ............................................................................ 27 1.4.3 Molecular Techniques ........................................................................................... 28 1.4.4 Indirect Methods of Microbial Detection .............................................................. 31 1.5 Prevention and Control ................................................................................................ 32 1.6 Anti-Microbial Surfaces: Examples and Actions ........................................................... 37 1.7 Historical use of Silver as an Antimicrobial ................................................................... 39 1.8 Uses of Silver compounds and Coatings ......................................................................
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