The main objective of this study was the characterization of surface associated microbial communities in breweries. In addition, the beer-spoiling potential of isolated strains and biofilm samples was investigated. Some studies reported the identity of cultivatable organisms from industrial plants. However, there were no data available about the composition of biofilm communities from these habitats for cultivation-independent techniques. Consequently, the fatty acid methyl esters (FAMEs) analysis, the fluorescence in situ hybridization (FISH) and the construction and investigation of 16S rRNA gene clone libraries were applied to reveal the structure of these communities. All of these methods have different advantages and therefore, they complement each other to get a more reliable picture of the biofilm communities.
The cultivation method was included in this study because it enables a verification of results from other studies. Furthermore, the obtained strains are genuine brewery isolates and can be used for physiological tests. Isolates were obtained from seven different sample sites (Chapter 1 and 5). They were identified and affiliated to 25 different genera. Some of these strains were inoculated in beer but none of them was able to grow in it (Chapter 1 and 5). However, these strains can still be harmful for the industry, e.g. if they are able to form biofilms. This aspect was investigated by analyzing the potential of the isolates to produce acyl-homoserine lactones (AHLs) (Chapter 6). These quorum sensing mediating molecules are involved in the maturation process of biofilms. Indeed, some strains were found to secrete these autoinducer molecules, they mainly belonged to the genus Pseudomonas.
An abundant proportion among the isolates was constituted by members of the Enterobacteriaceae (Chapter 7). In the beginning of this study, there was a minor suspicion concerning their beer-spoiling potential. Indeed, all isolated Enterobacteriaceae were found to be able to multiply in non-alcoholic beer under access of oxygen but they represented no risk for filled beer.
The beer-spoiling potential of biofilm communities was investigated by inoculating them in beer (Chapter 3). These enrichments allowed the detection of minor proportions of beer-spoiling organisms. About 25% of the biofilms contained microorganisms which were able to multiply in beer with 4.8% of ethanol (v/v). The absence of anaerobic beer-spoiling bacteria in most of the biofilms was confirmed by using specific FISH probes for Pectinatus and Megasphaera cells (Chapter 9). However, Pectinatus cells constituted one of the most abundant groups in two biofilm communities. These samples clearly demonstrated that brewery biofilms can become hazardous for the quality of the product.
The acetic acid bacteria were supposed to be abundant brewery biofilm organisms. This was not confirmed by any method used (Chapter 8). Instead, FISH signals were found for many other taxa in considerable proportions, e.g. communities from the conveyors consisted of members of the Eukarya, Archaea, Alpha-, Beta-, Gammaproteobacteria, Cytophaga-Flavobacteria, Planctomycetales, Actinobacteria and Firmicutes (Chapter 1). Such diverse communities were also evidenced for three other biofilms analyzed by FISH (Chapter 2 and 9).
Whereas the FISH technique allows the specific detection of single cells, the FAME analysis targets all organisms present, except the Archaea. The fatty acid profiles of 78 biofilms indicated significant differences between the communities, even between those which were exposed to similar conditions. In addition, repeated sampling of identical sites revealed a temporal variability of the microbial communities (Chapter 3). Characteristical fatty acids of beer-spoiling bacteria were almost absent. Typical fatty acids of Eukarya dominated nearly half of all biofilms. The high proportions of Eukarya in some biofilms was not confirmed, as these samples were also investigated by FISH. This divergence was found to be due to the higher biomass of eukaryotic cells compared to bacterial cells (Chapter 3). As some wild yeast strains were isolated and characterized, they are a potential source of these fatty acids. In contrast to the revealed bacterial diversity, most of the isolated yeasts were assigned to Saccharomyces or Candida spp. (Chapter 4). The Saccharomyces spp. showed a high beer-spoiling potential and many Candida species were able to form biofilms.
The construction of 16S rRNA gene clone libraries and the analysis of the clones with amplified ribosomal DNA restriction analysis (ARDRA) was performed with two biofilm communities (Chapter 2). Clones with identical ARDRA patterns were grouped and some representatives were identified by sequencing. These clone sequences were affiliated to 30 different genera, most of which were members of the Alpha- and Gammaproteobacteria and the Bacteroidetes. In addition, some clone sequences were assigned to uncultured organisms. Despite of the presence of 53 and 59 different ARDRA patterns in the two clone libraries, respectively, they had only four patterns in common. This result underlined the differences in the microbial composition of these communities.
In conclusion, breweries represent a habitat with high cleaning and disinfecting pressure, which might have selected for a limited number of more resistant or adopted species. Instead, the community structures of biofilms in industrial environments were found to be diverse and variable in their compositions.
| Identifer | oai:union.ndltd.org:uni-osnabrueck.de/oai:repositorium.ub.uni-osnabrueck.de:urn:nbn:de:gbv:700-2005012011 |
| Date | 20 January 2005 |
| Creators | Timke, Markus |
| Contributors | Priv.-Doz. Dr. André Lipski, Prof. Dr. Hans-Curt Flemming |
| Source Sets | Universität Osnabrück |
| Language | English |
| Detected Language | English |
| Type | doc-type:doctoralThesis |
| Format | application/zip, application/pdf |
| Rights | http://rightsstatements.org/vocab/InC/1.0/ |
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