1.1-billion-year-old porphyrins establish a marine ecosystem dominated by bacterial primary producers.

The average cell size of marine phytoplankton is critical for the flow of energy and nutrients from the base of the food web to higher trophic levels. Thus, the evolutionary succession of primary producers through Earth's history is important for our understanding of the radiation of modern protists ∼800 million years ago and the emergence of eumetazoan animals ∼200 million years later. Currently, it is difficult to establish connections between primary production and the proliferation of large and complex organisms because the mid-Proterozoic (∼1,800-800 million years ago) rock record is nearly devoid of recognizable phytoplankton fossils. We report the discovery of intact porphyrins, the molecular fossils of chlorophylls, from 1,100-million-year-old marine black shales of the Taoudeni Basin (Mauritania), 600 million years older than previous findings. The porphyrin nitrogen isotopes (δ15Npor = 5.6-10.2‰) are heavier than in younger sedimentary sequences, and the isotopic offset between sedimentary bulk nitrogen and porphyrins (εpor = -5.1 to -0.5‰) points to cyanobacteria as dominant primary producers. Based on fossil carotenoids, anoxygenic green (Chlorobiacea) and purple sulfur bacteria (Chromatiaceae) also contributed to photosynthate. The low εpor values, in combination with a lack of diagnostic eukaryotic steranes in the time interval of 1,600-1,000 million years ago, demonstrate that algae played an insignificant role in mid-Proterozoic oceans. The paucity of algae and the small cell size of bacterial phytoplankton may have curtailed the flow of energy to higher trophic levels, potentially contributing to a diminished evolutionary pace toward complex eukaryotic ecosystems and large and active organisms.

Efficient recycling of nutrients in modern and past hypersaline environments.

The biogeochemistry of hypersaline environments is strongly influenced by changes in biological processes and physicochemical parameters. Although massive evaporation events have occurred repeatedly throughout Earth history, their biogeochemical cycles and global impact remain poorly understood. Here, we provide the first nitrogen isotopic data for nutrients and chloropigments from modern shallow hypersaline environments (solar salterns, Trapani, Italy) and apply the obtained insights to δ15N signatures of the Messinian salinity crisis (MSC) in the late Miocene. Concentrations and δ15N of chlorophyll a, bacteriochlorophyll a, nitrate, and ammonium in benthic microbial mats indicate that inhibition of nitrification suppresses denitrification and anammox, resulting in efficient ammonium recycling within the mats and high primary productivity. We also suggest that the release of 15N-depleted NH3(gas) with increasing salinity enriches ammonium 15N in surface brine (≈34.0‰). Such elevated δ15N is also recorded in geoporphyrins isolated from sediments of the MSC peak (≈20‰), reflecting ammonium supply sufficient for sustaining phototrophic primary production. We propose that efficient nutrient supply combined with frequent bottom-water anoxia and capping of organic-rich sediments by evaporites of the Mediterranean MSC could have contributed to atmospheric CO2 reduction during the late Miocene.

DEEP BIOSPHERE. Exploring deep microbial life in coal-bearing sediment down to ~2.5 km below the ocean floor.

Microbial life inhabits deeply buried marine sediments, but the extent of this vast ecosystem remains poorly constrained. Here we provide evidence for the existence of microbial communities in ~40° to 60°C sediment associated with lignite coal beds at ~1.5 to 2.5 km below the seafloor in the Pacific Ocean off Japan. Microbial methanogenesis was indicated by the isotopic compositions of methane and carbon dioxide, biomarkers, cultivation data, and gas compositions. Concentrations of indigenous microbial cells below 1.5 km ranged from <10 to ~10(4) cells cm(-3). Peak concentrations occurred in lignite layers, where communities differed markedly from shallower subseafloor communities and instead resembled organotrophic communities in forest soils. This suggests that terrigenous sediments retain indigenous community members tens of millions of years after burial in the seabed.

[Clinical effect of arbekacin on MRSA infections after gastrointestinal surgery].

From January 1991 to July 1993, 58 patients with MRSA infections in our clinic at Wakayama Medical College and six affiliated hospitals were administered with arbekacin (ABK). The clinical results were as follows: 1. The clinical efficacy rates of ABK were 84% in pneumonia, 100% in both wound infections and hepatobiliary tract infections, and 85% in total. The bacteriological efficacy rate was 83%. 2. Regarding the administration route, the clinical efficacy rates were 60-79% by the intravenous treatment and inhalation therapy. Especially by the local administration with ABK, MRSA was eradicated in all cases. 3. The sufficient efficacy was obtained by the treatment of ABK alone (89%) and by the combined treatment with ABK (82%) and another antibiotics. From these results, it is concluded that ABK is useful for the treatment of MRSA infections after gastrointestinal surgery.

Evidence of global chlorophyll d.

Although analyses of chlorophyll d (Chl d)-dominated oxygenic photosystems have been conducted since their discovery 12 years ago, Chl d distribution in the environment and quantitative importance for aquatic photosynthesis remain to be investigated. We analyzed the pigment compositions of surface sediments and detected Chl d and its derivatives from diverse aquatic environments. Our data show that the viable habitat for Chl d-producing phototrophs extends across salinities of 0 to 50 practical salinity units and temperatures of 1 degrees to 40 degrees C, suggesting that Chl d production can be ubiquitously observed in aquatic environments that receive near-infrared light. The relative abundances of Chl d derivatives over that of Chl a derivatives in the studied samples are up to 4%, further suggesting that Chl d-based photosynthesis plays a quantitatively important role in the aquatic photosynthesis.

Induction of specific tolerance by hepatic double-negative CD4-8- alpha beta T cells of mice immunized with allogeneic cells via the portal vein in vivo [corrected].

We immunized AKR/n (H-2k) spleen cells in BALB/c (H-2d) mice via the portal vein (pv) and investigated the role of hepatic mononuclear cells (MNC) in the induction of alloantigen-specific immune tolerance. MNC in the liver and spleen of pv-administered mice were demonstrated to abrogate the responses to AKR/n alloantigens in allogeneic MLR. On the contrary, MNC in the liver and spleen of mice administered subcutaneously with the same antigens showed greater responses than those of control mice. The tolerance induced by pv administration was alloantigen-specific and appeared earlier in hepatic MNC than in splenic MNC. Furthermore, hepatic MNC of pv-administered mice had a suppressive effect when these cells were added to allogeneic MLR, in which mitomycin C (MMC)-treated AKR/n splenic MNC were used as stimulator and control BALB/c splenic MNC were used as responder. Splenic MNC of pv-administered mice and hepatic MNC of control mice did not show such suppressive effects. Such suppression was alloantigen-specific, since no suppression was induced when hepatic MNC of pv-administered mice were added to a system using MMC-treated C57BL/6 (H-2b) splenic MNC. The alloantigen-specific suppression induced by hepatic MNC was abrogated by a depletion of TcR-alpha beta + cells but not of CD4+, CD8+, nor B220+ cells from hepatic MNC. These results suggested that alloantigen-specific suppressor cells appeared predominantly in the hepatic MNC of pv-administered mice and displayed the phenotype of TcR-alpha beta +CD4-8- double-negative T cells, although alloantigen-specific tolerance was induced in both hepatic and splenic MNC.