Microbiota and Microsatellite genotypes of Pacific oysters stemming from three oyster bed in the Northern Wadden Sea

Background: Studies of oyster microbiomes have revealed that a limited number of microbes, including pathogens, can dominate microbial communities in host tissues such as gills and gut. Much of the bacterial diversity however remains underexplored and unexplained, although environmental conditions and host genetics have been implicated. We used 454 next generation 16S rRNA amplicon sequencing of individually tagged PCR reactions to explore the diversity of bacterial communities in gill tissue of the invasive Pacific oyster Crassostrea gigas stemming from genetically differentiated beds under ambient outdoor conditions and after a multifaceted disturbance treatment imposing stress on the host. Results: While the gill associated microbial communities in oysters were dominated by few abundant taxa (i.e. Sphingomonas, Mycoplasma) the distribution of rare bacterial groups correlated to relatedness between the hosts under ambient conditions. Exposing the host to disturbance broke apart this relationship by removing rare phylotypes thereby reducing overall microbial diversity. Shifts in the microbiome composition in response to stress did not result in a net increase in genera known to contain potentially pathogenic strains. Conclusion: The decrease in microbial diversity and the disassociation between population genetic structure of the hosts and their associated microbiome suggest that disturbance (i.e. stress) may play a significant role for the assembly of the natural microbiome. Such community shifts may in turn also feed back on the course of disease and the occurrence of mass mortality events in oyster populations.

Silicoflagellates of ODP Leg 119 samples

The occurrence of Quaternary and Oligocene silicoflagellates at two Ocean Drilling Program (ODP) Leg 119 Holes (736A and 744A) on the Kerguelen Plateau in the Southern Ocean was investigated to compare species distributions to Northern Hemisphere floras. This abstract gives the data determined (Tables 1 and 2) for 24 samples and few preliminary remarks. Quaternary assemblages of Hole 736A are noteworthy for the absences of key North Pacific zonal guide species such as Bachmannocena quadrangula, Dictyocha aculeata, Dictyocha subarctios, and Distephanus octangulatus (Bukry and Monechi, 1985). Other species such as Distephanus floridus, Distephanus speculum elongatus, and Mesocena octagona show limited ranges in Hole 736A and may help to subdivide the Quaternary locally. The late Oligocene assemblages of Hole 744A contain widely distributed species of Distephanus and Naviculopsis, which permit correlation to lower latitude assemblages. They also contain the high-latitude acme of Distephanus raupii which was first noted at Deep Sea Drilling Project (DSDP) Hole 278 (56°3.42'S, 160°04.29'E, water depth 3689 m) by Perch-Nielsen (1975) and Bukry (1975). Study of Hole 744A assemblages suggests that D. raupii developed from pentagonal Dictyocha deflandrei deflandrei. A final note on the Hole 744A assemblages is the brief late Oligocene acme (25%) of Dictyocha sp. aff. D. spinosa in Sample 119-744A-13H-4, 65-67 cm, which provides a direct correlation to the acme (16%) in DSDP Sample 29-278-31R-CC (Perch-Nielsen, 1975) in the Southern Ocean. Most of the taxonomy used in the tables is documented in earlier publications of the DSDP Initial Reports (see Bukry in Volumes 16, 35, 37, 40, 44, 49, 54, 67, 68, 69, 81, and 95). Also, see Loeblich et al. (1968) and Perch-Nielsen (1985) for extensive taxonomy and illustrations.

Range chart for Tertiary ostracodes from ODP Hole 101-628A (Table 1)

The Oligocene to Pliocene section from Hole 628A supplied about 100 species of Tertiary ostracodes. Deep-sea psychrospheric? species (Bradleya cf. dictyon, Agrenocythere cf. gosnoldia, Cardobairdia spp., Henryhowella sp., Cytheropteron spp., etc.) are present throughout the section. Starting in the Miocene, neritic species (Hulingsina sp., Puriana spp., Caudites spp., Loxoconcha fischeri, Cytherelloidea sp., etc.) dominate. Redeposition of these species from the continental shelf seems to be penecontemporaneous with sedimentation. Variations in the assemblages indicate biostratigraphic position. Species having an ecologic or stratigraphic importance are discussed and illustrated.

Biostratigraphical investigations of Lago d'Averno, near Naples

Remains of diatoms, molluscs, ostracods, foraminifera and pollen exines preserved in the sediments of Lago d'Averno, a volcanic lake in the Phlegrean Fields west of Naples, allowed us to reconstruct the changes in the ecological conditions of the lake and of the vegetation around it for the period from 800 BC to 800 AD. Lago d'Averno was at first a freshwater lake, temporarily influenced by volcanic springs. Salinity increased slowly during Greek times as a result of subsidence of the surrounding land. Saline conditions developed only after the lake was connected with the sea by a canal, when Portus Julius was built in 37 BC. The first post-Roman period of uplift ended with a short freshwater phase during the 7th century after Christ. Deciduous oakwoods around the lake was transformed into a forest of evergreen oaks in Greek times and thrived there - apparently almost uninfluenced by man - until it was felled, when the Avernus was incorporated into the new Roman harbour in 37 BC, to construct a shipyard and other military buildings there. Land-use was never more intense than during Roman times and weakest in Greek and Early Roman times, when the Avernus was considered a holy place, the entrance to the underworld.

A negative regulator mediates quorum-sensing control of exopolysaccharide production in Pantoea stewartii subsp. stewartii

Classical quorum-sensing (autoinduction) regulation, as exemplified by the lux system of Vibrio fischeri, requires N-acyl homoserine lactone (AHL) signals to stimulate cognate transcriptional activators for the cell density-dependent expression of specific target gene systems. For Pantoea stewartii subsp. stewartii, a bacterial pathogen of sweet corn and maize, the extracellular polysaccharide (EPS) stewartan is a major virulence factor, and its production is controlled by quorum sensing in a population density-dependent manner. Two genes, esaI and esaR, encode essential regulatory proteins for quorum sensing. EsaI is the AHL signal synthase, and EsaR is the cognate gene regulator. esaI, ΔesaR, and ΔesaI-esaR mutations were constructed to establish the regulatory role of EsaR. We report here that strains containing an esaR mutation produce high levels of EPS independently of cell density and in the absence of the AHL signal. Our data indicate that quorum-sensing regulation in P. s. subsp. stewartii, in contrast to most other described systems, uses EsaR to repress EPS synthesis at low cell density, and that derepression requires micromolar amounts of AHL. In addition, derepressed esaR strains, which synthesize EPS constitutively at low cell densities, were significantly less virulent than the wild-type parent. This finding suggests that quorum sensing in P. s. subsp. stewartii may be a mechanism to delay the expression of EPS during the early stages of infection so that it does not interfere with other mechanisms of pathogenesis.

Establishment of an animal–bacterial association: Recruiting symbiotic vibrios from the environment

While most animal–bacterial symbioses are reestablished each successive generation, the mechanisms by which the host and its potential microbial partners ensure tissue colonization remain largely undescribed. We used the model association between the squid Euprymna scolopes and Vibrio fischeri to examine this process. This light organ symbiosis is initiated when V. fischeri cells present in the surrounding seawater enter pores on the surface of the nascent organ and colonize deep epithelia-lined crypts. We discovered that when newly hatched squid were experimentally exposed to natural seawater, the animals responded by secreting a viscous material from the pores of the organ. Animals maintained in filtered seawater produced no secretions unless Gram-negative bacteria, either living or dead, were reintroduced. The viscous material bound only lectins that are specific for either N-acetylneuraminic acid or N-acetylgalactosamine, suggesting that it was composed of a mucus-containing matrix. Complex ciliated fields on the surface of the organ produced water currents that focused the matrix into a mass that was tethered to, and suspended above, the light organ pores. When V. fischeri cells were introduced into the seawater surrounding the squid, the bacteria were drawn into its fluid-filled body cavity during ventilation and were captured in the matrix. After residing as an aggregate for several hours, the symbionts migrated into the pores and colonized the crypt epithelia. This mode of infection may be an example of a widespread strategy by which aquatic hosts increase the likelihood of successful colonization by rarely encountered symbionts.

De miraculis vivorum seu De varia natura, varis singularitatibus, proprietatibus, affectionibus, mirandisque virtutibus, facultatibus & signis hominum viuorum ... /

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