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Biogas plants continuously convert biological wastes mainly into a mixture of methane, CO2 and H2O-a conversion that is carried out by a consortium of bacteria and archaea. Especially in the municipal plants dedicated towards waste treatment, the reactor feed may vary considerably, exposing the resident microbiota to a changing variety of substrates. To evaluate how and if such changes influence the microbiology, an established biogas plant (6,600 m3, up to 600 m3 biogas per h) was followed over the course of more than 2 years via polymerase chain reaction-denaturing gradient gel electrophoresis of 16S rRNA genes and subsequent sequencing. Both the bacterial and the archaeal community remained stable over the investigation. Of the bacterial consortium, about half of the sequences were in decreasing order of occurrence: Thermoacetogenium sp., Anaerobaculum mobile, Clostridium ultunense, Petrotoga sp., Lactobacillus hammesii, Butyrivibrio sp., Syntrophococcus sucromutans, Olsenella sp., Tepidanaerobacter sp., Sporanaerobacter acetigenes, Pseudoramibacter alactolyticus, Lactobacillus fuchuensis or Lactobacillus sakei, Lactobacillus parabrevis or Lactobacillus spicheri and Enterococcus faecalis. The other half matched closely to ones from similar habitats (thermophilic anaerobic methanogenic digestion). The archaea consisted of Methanobrevibacter sp., Methanoculleus bourgensis, Methanosphaera stadtmanae, Methanimicrococcus blatticola and uncultured Methanomicrobiales. The role of these species in methane production is discussed.

Bacteriophage-based assays and biosensors rival traditional antibodybased immunoassays for detection of low-level Salmonella contaminations. In this study, we harnessed the binding specificity of the long tail fiber (LTF) from bacteriophage S16 as an affinity molecule for the immobilization, enrichment, and detection of Salmonella. We demonstrate that paramagnetic beads (MBs) coated with recombinant gp37-gp38 LTF complexes (LTF-MBs) are highly effective tools for rapid affinity magnetic separation and enrichment of Salmonella. Within 45 min, the LTF-MBs consistently captured over 95% of Salmonella enterica serovar Typhimurium cells from suspensions containing from 10 to 10 5 CFU · ml Ϫ1 , and they yielded equivalent recovery rates (93% Ϯ 5%, n ϭ 10) for other Salmonella strains tested. LTF-MBs also captured Salmonella cells from various food sample preenrichments, allowing the detection of initial contaminations of 1 to 10 CFU per 25 g or ml. While plating of bead-captured cells allowed ultrasensitive but time-consuming detection, the integration of LTF-based enrichment into a sandwich assay with horseradish peroxidaseconjugated LTF (HRP-LTF) as a detection probe produced a rapid and easy-to-use Salmonella detection assay. The novel enzyme-linked LTF assay (ELLTA) uses HRP-LTF to label bead-captured Salmonella cells for subsequent identification by HRP-catalyzed conversion of chromogenic 3,3=,5,5=-tetramethylbenzidine substrate. The color development was proportional for Salmonella concentrations between 10 2 and 10 7 CFU · ml Ϫ1 as determined by spectrophotometric quantification. The ELLTA assay took 2 h to complete and detected as few as 10 2 CFU · ml Ϫ1 S. Typhimurium cells. It positively identified 21 different Salmonella strains, with no cross-reactivity for other bacteria. In conclusion, the phage-based ELLTA represents a rapid, sensitive, and specific diagnostic assay that appears to be superior to other currently available tests. IMPORTANCEThe incidence of foodborne diseases has increased over the years, resulting in major global public health issues. Conventional methods for pathogen detection can be laborious and expensive, and they require lengthy preenrichment steps. Rapid enrichment-based diagnostic assays, such as immunomagnetic separation, can reduce detection times while also remaining sensitive and specific. A critical component in these tests is implementing affinity molecules that retain the ability to specifically capture target pathogens over a wide range of in situ applications. The protein complex that forms the distal tip of the bacteriophage S16 long tail fiber is shown here to represent a highly sensitive affinity molecule for the specific enrichment and detection of Salmonella. Phage-encoded long tail fibers have huge potential for development as novel affinity molecules for robust and specific diagnostics of a vast spectrum of bacteria.

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