Dataset Information

Historical Factors Associated With Past Environments Influence the Biogeography of Thermophilic Endospores in Arctic Marine Sediments.

ABSTRACT: Selection by the local, contemporary environment plays a prominent role in shaping the biogeography of microbes. However, the importance of historical factors in microbial biogeography is more debatable. Historical factors include past ecological and evolutionary circumstances that may have influenced present-day microbial diversity, such as dispersal and past environmental conditions. Diverse thermophilic sulfate-reducing Desulfotomaculum are present as dormant endospores in marine sediments worldwide where temperatures are too low to support their growth. Therefore, they are dispersed to here from elsewhere, presumably a hot, anoxic habitat. While dispersal through ocean currents must influence their distribution in cold marine sediments, it is not clear whether even earlier historical factors, related to the source habitat where these organisms were once active, also have an effect. We investigated whether these historical factors may have influenced the diversity and distribution of thermophilic endospores by comparing their diversity in 10 Arctic fjord surface sediments. Although community composition varied spatially, clear biogeographic patterns were only evident at a high level of taxonomic resolution (>97% sequence similarity of the 16S rRNA gene) achieved with oligotyping. In particular, the diversity and distribution of oligotypes differed for the two most prominent OTUs (defined using a standard 97% similarity cutoff). One OTU was dominated by a single ubiquitous oligotype, while the other OTU consisted of ten more spatially localized oligotypes that decreased in compositional similarity with geographic distance. These patterns are consistent with differences in historical factors that occurred when and where the taxa were once active, prior to sporulation. Further, the influence of history on biogeographic patterns was only revealed by analyzing microdiversity within OTUs, suggesting that populations within standard OTU-level groupings do not necessarily share a common ecological and evolutionary history.

SUBMITTER: Hanson CA

PROVIDER: S-EPMC6403435 | biostudies-literature | 2019

REPOSITORIES: biostudies-literature

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Historical Factors Associated With Past Environments Influence the Biogeography of Thermophilic Endospores in Arctic Marine Sediments.

Hanson China A CA Müller Albert L AL Loy Alexander A Dona Clelia C Appel Ramona R Jørgensen Bo Barker BB Hubert Casey R J CRJ

Frontiers in microbiology 20190228

Selection by the local, contemporary environment plays a prominent role in shaping the biogeography of microbes. However, the importance of historical factors in microbial biogeography is more debatable. Historical factors include past ecological and evolutionary circumstances that may have influenced present-day microbial diversity, such as dispersal and past environmental conditions. Diverse thermophilic sulfate-reducing <i>Desulfotomaculum</i> are present as dormant endospores in marine sedim ...[more]

PMID: 30873129

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Project description:Dormant endospores of anaerobic, thermophilic bacteria found in cold marine sediments offer a useful model for studying microbial biogeography, dispersal, and survival. The dormant endospore phenotype confers resistance to unfavorable environmental conditions, allowing dispersal to be isolated and studied independently of other factors such as environmental selection. To study the resilience of thermospores to conditions relevant for survival in extreme cold conditions, their viability following different freezing treatments was tested. Marine sediment was frozen at either -80°C or -20°C for 10 days prior to pasteurization and incubation at +50°C for 21 days to assess thermospore viability. Sulfate reduction commenced at +50°C following both freezing pretreatments indicating persistence of thermophilic endospores of sulfate-reducing bacteria. The onset of sulfate reduction at +50°C was delayed in -80°C pretreated microcosms, which exhibited more variability between triplicates, compared to -20°C pretreated microcosms and parallel controls that were not frozen in advance. Microbial communities were evaluated by 16S rRNA gene amplicon sequencing, revealing an increase in the relative sequence abundance of thermophilic endospore-forming Firmicutes in all microcosms. Different freezing pretreatments (-80°C and -20°C) did not appreciably influence the shift in overall bacterial community composition that occurred during the +50°C incubations. Communities that had been frozen prior to +50°C incubation showed an increase in the relative sequence abundance of operational taxonomic units (OTUs) affiliated with the class Bacilli, relative to unfrozen controls. These results show that freezing impacts but does not obliterate thermospore populations and their ability to germinate and grow under appropriate conditions. Indeed the majority of the thermospore OTUs detected in this study (21 of 22) could be observed following one or both freezing treatments. These results are important for assessing thermospore viability in frozen samples and following cold exposure such as the very low temperatures that would be encountered during panspermia.

Project description:Cold marine sediments harbor endospores of fermentative and sulfate-reducing, thermophilic bacteria. These dormant populations of endospores are believed to accumulate in the seabed via passive dispersal by ocean currents followed by sedimentation from the water column. However, the magnitude of this process is poorly understood because the endospores present in seawater were so far not identified, and only the abundance of thermophilic sulfate-reducing endospores in the seabed has been quantified. We investigated the distribution of thermophilic fermentative endospores (TFEs) in water column and sediment of Aarhus Bay, Denmark, to test the role of suspended dispersal and determine the rate of endospore deposition and the endospore abundance in the sediment. We furthermore aimed to determine the time course of reactivation of the germinating TFEs. TFEs were induced to germinate and grow by incubating pasteurized sediment and water samples anaerobically at 50°C. We observed a sudden release of the endospore component dipicolinic acid immediately upon incubation suggesting fast endospore reactivation in response to heating. Volatile fatty acids (VFAs) and H2 began to accumulate exponentially after 3.5 h of incubation showing that reactivation was followed by a short phase of outgrowth before germinated cells began to divide. Thermophilic fermenters were mainly present in the sediment as endospores because the rate of VFA accumulation was identical in pasteurized and non-pasteurized samples. Germinating TFEs were identified taxonomically by reverse transcription, PCR amplification and sequencing of 16S rRNA. The water column and sediment shared the same phylotypes, thereby confirming the potential for seawater dispersal. The abundance of TFEs was estimated by most probable number enumeration, rates of VFA production, and released amounts of dipicolinic acid during germination. The surface sediment contained ∼105-106 inducible TFEs cm-3. TFEs thus outnumber thermophilic sulfate-reducing endospores by an order of magnitude. The abundance of cultivable TFEs decreased exponentially with sediment depth with a half-life of 350 years. We estimate that 6 × 109 anaerobic thermophilic endospores are deposited on the seafloor per m2 per year in Aarhus Bay, and that these thermophiles represent >10% of the total endospore community in the surface sediment.

Project description:Simple Summary Earwigs (Dermaptera) have their highest diversity in the tropical areas of the southern hemisphere, whereas the temperate regions of the northern hemisphere have relatively few species. This pattern has been considered a reflection of their origin in Gondwana, the supercontinent that grouped most of the land masses in today’s southern hemisphere, including Antarctica, South America, Africa and Madagascar. An analysis of the distributions of the major evolutionary lineages of earwigs supports the role of the Gondwanan breakup in determining the current patterns of their diversity, as well the influence of the Indian collision with the Eurasian plate. The dispersal into the Eurasian plate was largely constrained by the Himalayan orogenesis and the presence of colder temperatures. This climatic barrier was probably the most important factor that largely hampered the colonization of North America from South America. Abstract The Dermaptera are an insect order exhibiting their highest diversity in the tropical areas of the southern hemisphere. This pattern has been considered a reflection of a Gondwanan origin. However, this hypothesis has not been tested through analytical methods. In this paper, the world distribution of earwigs was analysed by using the ‘Cladistic Analysis of Distributions and Endemism’ (CADE), a method which groups areas of endemism on the basis of shared distributions and phylogenetic relationships among taxa. In addition, clustering techniques were applied to depict biotic relationships based on similarity indices. Results of CADE support the idea that Gondwanan fragmentation exerted a crucial role in shaping the current distribution of the main clades of earwigs. However, the relationships between India with South East Asia suggested a biotic interchange occurred after the Indian collision with the Eurasian plate. The overall scenario emerging from cluster analyses revealed a strong influence of dispersal events. Overall, the distribution of earwig major clades indicates that their biogeographical history was mainly characterized by vicariance events (led by the break-up of Gondwana) followed by large scale dispersal processes constrained by the Himalayan orogenesis and the presence of colder temperatures, which have largely hampered the colonization of the northern hemisphere.

Dataset Information

Historical Factors Associated With Past Environments Influence the Biogeography of Thermophilic Endospores in Arctic Marine Sediments.

Publications

Historical Factors Associated With Past Environments Influence the Biogeography of Thermophilic Endospores in Arctic Marine Sediments.

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