Microbial Biodiversity of Thermophilic Communities in Hot Mineral Soils of Tramway Ridge, Mt. Erebus, Antarctica

Only a few studies have looked at microbial biogeography in soils and whether microorganisms are endemic to an area is still debatable. Tramway Ridge, a geothermal area on Mount Erebus, Antarctica, provides a unique opportunity due to its isolation and extreme conditions to explore the possibilities of microbial endemism and to identify novel Bacteria and Archaea. This site was chosen for a culture-independent study with a preliminary culturing survey for bacterial communities along three temperature gradients (65 C - 2.5'C). In addition, a physico-chemical analysis was undertaken to identify which environmental factors were driving the different diversity along the transects. An automated rRNA intergenic spacer analysis (ARISA) was used to assess the diversity across the transects using Bacteria and Cyanobacteria-specific primers and results showed that temperature and pH were the main drivers for these communities. Due to its unique physico-chemical and ARISA profile, a hot temperature site (T-3A, 65'C) was chosen for further investigation by bacterial and archaeal 16S rDNA clone libraries. Unique rDNA types among the 78 bacterial and 83 archaeal clones were identified by restriction fragment length polymophisms and 18 bacterial and 5 archaeal operational taxonomic units (gt97% identity) were observed. All of the bacterial sequences were deeply branching and loosely affiliated with other recognised bacterial divisions, with 40% of the sequences not affiliated to any genus. The archaeal clones were found to be deep-branching and sequences clustered together within the Crenarcaheota. In addition, two strains of Bacilli were isolated. The novel microorganisms show that the Tramway Ridge communities are unique from organisms found in other environments and show that quotEverything is (not) everywherequot

On the origins of oxygenic photosynthesis and aerobic respiration in Cyanobacteria

The origin of oxygenic photosynthesis in Cyanobacteria led to the rise of oxygen on Earth ~2.3 billion years ago, profoundly altering the course of evolution by facilitating the development of aerobic respiration and complex multicellular life. Here we report the genomes of 41 uncultured organisms related to the photosynthetic Cyanobacteria (class Oxyphotobacteria), including members of the class Melainabacteria and a new class of Cyanobacteria (class Sericytochromatia) that is basal to the Melainabacteria and Oxyphotobacteria. All members of the Melainabacteria and Sericytochromatia lack photosynthetic machinery, indicating that phototrophy was not an ancestral feature of the Cyanobacteria and that Oxyphotobacteria acquired the genes for photosynthesis relatively late in cyanobacterial evolution. We show that all three classes independently acquired aerobic respiratory complexes, supporting the hypothesis that aerobic respiration evolved after oxygenic photosynthesis

Coral-Bacterial Communities before and after a Coral Mass Spawning Event on Ningaloo Reef

Bacteria associated with three coral species, Acropora tenuis, Pocillopora damicornis and Tubastrea faulkneri, were assessed before and after coral mass spawning on Ningaloo Reef in Western Australia. Two colonies of each species were sampled before and after the mass spawning event and two additional samples were collected for P. damicornis after planulation. A variable 470 bp region of the 16 S rRNA gene was selected for pyrosequencing to provide an understanding of potential variations in coral-associated bacterial diversity and community structure. Bacterial diversity increased for all coral species after spawning as assessed by Chao1 diversity indicators. Minimal changes in community structure were observed at the class level and data at the taxonomical level of genus incorporated into a PCA analysis indicated that despite bacterial diversity increasing after spawning, coral-associated community structure did not shift greatly with samples grouped according to species. However, interesting changes could be detected from the dataset; for example, α-Proteobacteria increased in relative abundance after coral spawning and particularly the Roseobacter clade was found to be prominent in all coral species, indicating that this group may be important in coral reproduction

Evolution of photosynthesis and aerobic respiration in the cyanobacteria

For well over a hundred years, members of the bacterial phylum Cyanobacteria have been considered strictly photosynthetic microorganisms, reflected in their classification as “blue-green algae” in the botanical code. Recently, genomes recovered from environmental sequencing surveys representing two major uncultured basal lineages (classes) of Cyanobacteria have been found to completely lack photosynthetic and CO fixation genes. The most likely explanation for this finding is that oxygenic photosynthesis was not an ancestral feature of the Cyanobacteria, and rather originated following divergence of the primary lines of descent. Here we describe recent findings on the evolution of aerobic respiration in the non-photosynthetic cyanobacterial classes, and how this has been interpreted by researchers interested in the evolution of oxygenic photosynthesis

The larval sponge holobiont exhibits high thermal tolerance

Marine sponges are critical components of benthic environments; however, their sessile habit, requirement to filter large volumes of water and complex symbiotic partnerships make them particularly vulnerable to the effects of global climate change. We assessed the effect of elevated seawater temperature on bacterial communities in larvae of the Great Barrier Reef sponge, Rhopaloeides odorabile. In contrast to the strict thermal threshold of 32°C previously identified in adult R. odorabile, larvae exhibit a markedly higher thermal tolerance, with no adverse health effects detected at temperatures below 36°C. Similarly, larval microbial communities were conserved at temperatures up to 34°C with a highly significant shift occurring after 24 h at 36°C. This shift involved the loss of previously described symbionts (in particular the Nitrospira, Chloroflexi and a Roseobacter lineage) and the appearance of new Gammaproteobacteria not detected at lower temperatures. Here, we demonstrated that sponge larvae maintain highly stable symbioses at seawater temperatures exceeding those that are predicted under current climate change scenarios. In addition, by revealing that the shift in microbial composition occurs in conjunction with necrosis and mortality of larvae at 36°C we have provided additional evidence of the strong link between host health and the stability of symbiont communities

Maternal inheritance of the koala gut microbiome and its compositional and functional maturation during juvenile development

The acquisition and maturation of the gastrointestinal microbiome is a crucial aspect of mammalian development, particularly for specialist herbivores such as the koala (Phascolarctos cinereus). Joey koalas are thought to be inoculated with microorganisms by feeding on specialized maternal faeces (pap). We found that compared to faeces, pap has higher microbial density, higher microbial evenness and a higher proportion of rare taxa, which may facilitate the establishment of those taxa in joey koalas. We show that the microbiomes of captive joey koalas were on average more similar to those of their mothers than to other koalas, indicating strong maternal inheritance of the faecal microbiome, which can lead to intergenerational gut dysbiosis when the mother is ill. Directly after pap feeding, the joey koalas' microbiomes were enriched for milk-associated bacteria including Bacteroides fragilis, suggesting a conserved role for this species across mammalian taxa. The joeys' microbiomes then changed slowly over 5 months to resemble those of adults by 1 year of age. The relative abundance of fibrolytic bacteria and genes involved in the degradation of plant cell walls also increased in the infants over this time, likely in response to an increased proportion of Eucalyptus leaves in their diets

Introduzione

An uncultured non-photosynthetic basal lineage of the Cyanobacteria, the Melainabacteria, was recently characterised by metagenomic analyses of aphotic environmental samples. However, a predatory bacterium, Vampirovibrio chlorellavorus, originally described in 1972 appears to be the first cultured representative of the Melainabacteria based on a 16S rRNA sequence recovered from a lyophilised co-culture of the organism. Here, we sequenced the genome of V. chlorellavorus directly from 36 year-old lyophilised material that could not be resuscitated confirming its identity as a member of the Melainabacteria. We identified attributes in the genome that likely allow V. chlorellavorus to function as an obligate predator of the microalga Chlorella vulgaris, and predict that it is the first described predator to use an Agrobacterium tumefaciens-like conjugative type IV secretion system to invade its host. V. chlorellavorus is the first cyanobacterium recognised to have a predatory lifestyle and further supports the assertion that Melainabacteria are non-photosynthetic

Microbial biodiversity of thermophilic communities in hot mineral soils of Tramway Ridge, Mount Erebus, Antarctica

Tramway Ridge, located near the summit of Mount Erebus in Antarctica, is probably the most remote geothermal soil habitat on Earth. Steam fumaroles maintain moist, hot soil environments creating extreme local physicochemical differentials. In this study a culture-independent approach combining automated rRNA intergenic spacer analysis (ARISA) and a 16S rRNA gene library was used to characterize soil microbial (Bacterial and Archaeal) diversity along intense physicochemical gradients. Statistical analysis of ARISA data showed a clear delineation between bacterial community structure at sites close to fumaroles and all other sites. Temperature and pH were identified as the primary drivers of this demarcation. A clone library constructed from a high-temperature site led to the identification of 18 novel bacterial operational taxonomic units (OTUs). All 16S rRNA gene sequences were deep branching and distantly (85–93%) related to other environmental clones. Five of the signatures branched with an unknown group between candidate division OP10 and Chloroflexi. Within this clade, sequence similarity was low, suggesting it contains several yet-to-be described bacterial groups. Five archaeal OTUs were obtained and exhibited high levels of sequence similarity (95–97%) with Crenarchaeota sourced from deep-subsurface environments on two distant continents. The novel bacterial assemblage coupled with the unique archaeal affinities reinvigorates the hypotheses that Tramway Ridge organisms are relics of archaic microbial lineages specifically adapted to survive in this harsh environment and that this site may provide a portal to the deep-subsurface biosphere