Distinct partitioning has been observed in the composition and diversity of bacterial communities inhabiting the surface and overlying seawater of three coral species infected with black band disease (BBD) on the southern Caribbean island of Curaçao, Netherlands Antilles. PCR amplification and sequencing of bacterial 16S rRNA genes (rDNA) with universally conserved primers have identified over 524 unique bacterial sequences affiliated with 12 bacterial divisions. The molecular sequences exhibited less than 5% similarity in bacterial community composition between seawater and the healthy, black band diseased, and dead coral surfaces. The BBD bacterial mat rapidly migrates across and kills the coral tissue. Clone libraries constructed from the BBD mat were comprised of eight bacterial divisions and 13% unknowns. Several sequences representing bacteria previously found in other marine and terrestrial organisms (including humans) were isolated from the infected coral surfaces, including Clostridium spp., Arcobacter spp., Campylobacter spp., Cytophaga fermentans, Cytophaga columnaris, and Trichodesmium tenue.Infectious disease in scleractinian corals has emerged as one of the primary causes of the accelerating global destruction of coral reef ecosystems (22,25,27,56,74). Black band disease (BBD) is one of the most widespread and destructive of these coral infections (see review in reference 50). The diagnostic symptom of BBD is the development of a narrow 0.1-to 7-cmwide ring-shaped black to red microbial mat that migrates from top to bottom across massive coral colonies, killing healthy coral tissue at rates of as much as 1 cm per day (47, 53). BBD preferentially affects corals such as Montastrea annularis, Montastrea cavernosa, and Diploria strigosa (6,15,53). These species, known as framework building corals, form large structures that become the dominant physical elements of reefs. As a result, coral mortality caused by BBD is a potent force in restructuring coral reef ecosystems (15,36).There is considerable controversy as to whether BBD is caused by physical and chemical environmental stresses or is an infectious disease or both (50, 56). However, an impediment to determining the cause of BBD has been the lack of information about the diversity and distribution of microbial populations that inhabit normal healthy coral tissue and the BBD bacterial mat. It is known from studies of infectious disease in marine and terrestrial invertebrates, fish, and mammals (including humans) that pathogens are most effectively studied within an ecological context of interactions among microbes, their hosts, and the environmental conditions in which they live (25, 54). Accurate diagnosis and eventual treatment and prevention of BBD will therefore require a basic knowledge of the composition and distribution of the microbial communities associated with healthy as well as diseased organisms. This type of community-based comparative analysis of the microorganisms associated with infectious diseases in corals has not previously been...

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Dissecting ancient microbial sulfur cycling Before the rise of oxygen, life on Earth depended on the marine sulfur cycle. The fractionation of different sulfur isotopes provides clues to which biogeochemical cycles were active long ago (see the Perspective by Ueno). Zhelezinskaia et al. found negative isotope anomalies in Archean rocks from Brazil and posit that metabolic fluxes from sulfate-reducing microorganisms influenced the global sulfur cycle, including sulfur in the atmosphere. In contrast, Paris et al. found positive isotope anomalies in Archean sediments from South Africa, implying that the marine sulfate pool was more disconnected from atmospheric sulfur. As an analog for the Archean ocean, Crowe et al. measured sulfur isotope signatures in modern Lake Matano, Indonesia, and suggest that low seawater sulfate concentrations restricted early microbial activity. Science , this issue p. 703 , p. 742 , p. 739 ; see also p. 735

The origin and evolution of the atmospheres of Earth, Venus and Mars are reviewed from the time when their protoplanets were released from the protoplanetary disk a few million years after the Sun came into being. The early disk-embedded phase of the evolution of protoplanetary cores that can accumulate gas from the disk and form thin planetary H 2-envelopes is also discussed. This scenario is compared to cases of late stage planet formation, where terrestrial planets accrete from large planetary embryos after the protoplanetary disk already disappeared. The differences between these two scenarios are discussed by investigating non-radiogenic noble gas isotope anomalies observed in the present atmospheres of the three planets. The role of the efficiency of the young Sun's EUV radiation and solar wind to the escape of early atmospheres is also discussed. The catastrophic outgassing of volatiles and the formation and cooling of steam atmospheres after the solidification of magma oceans is addressed together with the geochemical evidence of additional delivery of volatile-rich chondritic materials during the main stages of planetary formation. Unlike early Venus and Earth, no nebula-based H 2-envelope could be accumulated on early Mars due to its low planetary mass. According to the young Sun's luminosity and EUV flux history, Mars' magma ocean related outgassed steam atmosphere could have been lost during the first hundred Myrs. Depending on the young Sun's EUV flux, the presence of greenhouse gases, impacts, and the amount of greenhouse gases outgassed additional to that from the magma ocean, Mars could have developed episodically standing bodies of liquid water

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