Research output: Book/anthology/dissertation/reportPh.D. thesisResearch

    Marta Volpi
Microbial biogeographical patterns are determined by three main processes: selection, diversification and dispersal. The presence of anaerobic thermophilic endospores in cold marine sediments enables us to study passive microbial dispersal in isolation from other processes that affect the composition of microbial communities. Since these endospores remain dormant in cold environments and are highly resistant to lysis, they are not subjected to selection and diversification during dispersal. Previous estimates of the magnitude of dispersal of thermophilic endospores in marine environments were solely based on endospores of sulphate-reducing bacteria (SRB), which presumably constitute only a small fraction of the total thermophilic endospore community reaching cold environments. My PhD project developed an experimental framework for using thermophilic fermentative endospores (TFEs) to trace passive microbial dispersal in the marine environment. TFEs show greater environmental abundances and are more readily enriched and cultivated than their sulfate-reducing counterparts. This work therefore represents a significant step forward in identifying the source environments of marine thermophilic endospores and in understanding their rates, routes and barriers of dispersal. We found that in Aarhus Bay (Denmark) TFEs are 100-fold more abundant than endospores of thermophilic SRB, with estimates of up to 6 × 106 TFEs mL-1 sediment. Those numbers are supported by four independent methods: most probable number enumeration, dipicolinic acid and metabolic rate measurements as well as microcalorimetry. Consequently, thermophilic endospores constitute more than 10% of the total endospore community in Aarhus Bay surface sediments, resulting from an influx of 5.8 × 109 endospores m-2 year-1.
For the first time we characterized the thermophilic endospore community in both sediment and seawater samples by 16S rRNA sequencing. Thermophilic endospores in sediment likely originated from seawater as all seawater phylotypes were also detected in the sediment. The most abundant type of TFEs in the sediment was most closely related to isolates and environmental sequences derived from terrestrial habitats, indicating that marine thermophilic endospores may be of terrestrial origin.
We isolated a novel thermophilic fermentative endospore-forming bacterial species from Aarhus Bay sediment. This species is identical to a phylotype of thermophilic endospores previously shown to be abundant and globally dispersed among marine sediments, and its characterization and genome sequence offered new general insights into the dispersal and ecophysiology of marine thermophilic endospores. Most notably based on long-term incubation experiments we conclude that the isolate is unable to grow at the in situ temperatures in sediments. This species therefore cannot persist in vegetative state in cold marine sediments and therefore its presence must result from dispersal from warm environments.
In conclusion, this work identifies TFEs as a powerful tool to study pathways and barriers of marine microbial dispersal and offers an experimental framework for examining their environmental abundance and diversity.
Original languageEnglish
Number of pages185
StatePublished - 2016

    Research areas

  • thermophiles, endospores, fermentative bacteria, Aarhus Bay

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