The end-Permian mass extinction was the most severe biodiversity crisis in Earth history. To better constrain the timing, and ultimately the causes of this event, we collected a suite of geochronologic, isotopic, and biostratigraphic data on several well-preserved sedimentary sections in South China. High-precision U-Pb dating reveals that the extinction peak occurred just before 252.28 ± 0.08 million years ago, after a decline of 2 per mil (‰) in δ(13)C over 90,000 years, and coincided with a δ(13)C excursion of -5‰ that is estimated to have lasted ≤20,000 years. The extinction interval was less than 200,000 years and synchronous in marine and terrestrial realms; associated charcoal-rich and soot-bearing layers indicate widespread wildfires on land. A massive release of thermogenic carbon dioxide and/or methane may have caused the catastrophic extinction.
Photosynthetic bacteria emerged on Earth more than 3 Gyr ago. To date, despite a long evolutionary history, species containing (bacterio)chlorophyll-based reaction centers have been reported in only 6 out of more than 30 formally described bacterial phyla: Cyanobacteria, Proteobacteria, Chlorobi, Chloroflexi, Firmicutes, and Acidobacteria. Here we describe a bacteriochlorophyll a-producing isolate AP64 that belongs to the poorly characterized phylum Gemmatimonadetes. This red-pigmented semiaerobic strain was isolated from a freshwater lake in the western Gobi Desert. It contains fully functional type 2 (pheophytin-quinone) photosynthetic reaction centers but does not assimilate inorganic carbon, suggesting that it performs a photoheterotrophic lifestyle. Full genome sequencing revealed the presence of a 42.3-kb-long photosynthesis gene cluster (PGC) in its genome. The organization and phylogeny of its photosynthesis genes suggests an ancient acquisition of PGC via horizontal transfer from purple phototrophic bacteria. The data presented here document that Gemmatimonadetes is the seventh bacterial phylum containing (bacterio)chlorophyllbased phototrophic species. To our knowledge, these data provide the first evidence that (bacterio)chlorophyll-based phototrophy can be transferred between distant bacterial phyla, providing new insights into the evolution of bacterial photosynthesis.anoxygenic photosynthesis | horizontal gene transfer | bacterial pigments | aerobic photoheterotroph | fluorescence imaging system
Aerobic anoxygenic phototrophic bacteria (AAPB) are an important bacterial group with capability of harvesting light energy, and appear to have a particular role in the ocean's carbon cycling. Yet the significance of AAPB relative to total bacteria (AAPB%) in different marine regimes are still controversial, and variation trend of genetic diversity of AAPB along environmental gradients remains unclear. Here we present the first comprehensive observation of the global distribution of AAPB in the Pacific, Atlantic and Indian oceans, revealing a general pattern of high abundance of AAPB and AAPB% in coastal waters than oceanic waters. The Indian Ocean contained relatively high AAPB% compared with the other two oceans, corresponding to the high primary production in this region. Both abundance of AAPB and AAPB% were positively correlated with the concentration of chlorophyll a, while the diversity of AAPB decreased with increasing chlorophyll a values. Our results suggest that AAPB abundance and diversity follow opposite trends from oligotrophic to eutrophic regimes in the ocean.
Bacterial diversity and cell abundance in the snow of the four glaciers (Guoqu, Zadang, East Rongbuk and Palong No. 4) located in different climatic zones of the Tibetan Plateau were investigated through culture-independent molecular analysis of 16S rRNA gene clone library and flow cytometry approaches. Cell abundance ranged from 0.68 x 10(3) to 720 x 10(3) cells mL(-1), with higher values in the northern glaciers than in the southern ones. Bacterial diversity was unexpectedly high in the snow habitats of the world's highest plateau, with 15 common genera distributed widely among the glaciers. The bacterial diversity in the snow at different glaciers was related to the surrounding environments. The Guoqu Glacier, to the north near the desert zone and with the lowest temperature, preserved more bacteria closely related to a cold environment and soil than the other glaciers. However, in the Palong No. 4 Glacier located in the south warm region around vegetation, most bacteria were phylogenetically related to plant-associated bacteria.
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