Abstract
BackgroundIn recent years biogas plants in Germany have been supposed to be involved in amplification and dissemination of pathogenic bacteria causing severe infections in humans and animals. In particular, biogas plants are discussed to contribute to the spreading of Escherichia coli infections in humans or chronic botulism in cattle caused by Clostridium botulinum. Metagenome datasets of microbial communities from an agricultural biogas plant as well as from anaerobic lab-scale digesters operating at different temperatures and conditions were analyzed for the presence of putative pathogenic bacteria and virulence determinants by various bioinformatic approaches.ResultsAll datasets featured a low abundance of reads that were taxonomically assigned to the genus Escherichia or further selected genera comprising pathogenic species. Higher numbers of reads were taxonomically assigned to the genus Clostridium. However, only very few sequences were predicted to originate from pathogenic clostridial species. Moreover, mapping of metagenome reads to complete genome sequences of selected pathogenic bacteria revealed that not the pathogenic species itself, but only species that are more or less related to pathogenic ones are present in the fermentation samples analyzed. Likewise, known virulence determinants could hardly be detected. Only a marginal number of reads showed similarity to sequences described in the Microbial Virulence Database MvirDB such as those encoding protein toxins, virulence proteins or antibiotic resistance determinants.ConclusionsFindings of this first study of metagenomic sequence reads of biogas producing microbial communities suggest that the risk of dissemination of pathogenic bacteria by application of digestates from biogas fermentations as fertilizers is low, because obtained results do not indicate the presence of putative pathogenic microorganisms in the samples analyzed.
Highlights
In recent years biogas plants in Germany have been supposed to be involved in amplification and dissemination of pathogenic bacteria causing severe infections in humans and animals
Origin and characteristics of metagenome sequence datasets consulted for searching of sequence tags originating from putative pathogenic bacteria are described in
CARMA3 classified 2,183,722 environmental gene tags (EGTs), comprising all datasets, while 176,780 of these EGTs were assigned to genus and 16,035 EGTs to species level
Summary
In recent years biogas plants in Germany have been supposed to be involved in amplification and dissemination of pathogenic bacteria causing severe infections in humans and animals. The recent outbreak of an enterohemorrhagic Escherichia coli O104:H4 strain in Germany in May 2011 is an example for a foodborne disease having vegetables as source of infection. This outbreak led to the infection of about 3,800 patients suffering from acute gastroenteritis or even the hemolytic-uremic syndrome. Epidemiological and surveillance studies were conducted at the same time by German federal institutions to identify the origin of infection These studies led to the hypothesis that contaminated vegetables like cucumbers or tomatoes might be involved in spreading of the human pathogenic bacterium [3,4,5]. Press coverage hypothesized that digestates from agricultural biogas reactors could have been a source causing these infections
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