Sulfate reduction is an essential metabolism that maintains biogeochemical cycles in marine and terrestrial ecosystems.Sulfate reducers are exclusively prokaryotic,phylogenetically diverse,and may have evolved early in Earth’s history.However,their origin is elusive and unequivocal fossils are lacking.Here we report a new microfossil,Qingjiangonema cambria,from518-million-year-old black shales that yield the Qingjiang biota.Qingjiangonema is a long filamentous form comprising hundreds of cells filled by equimorphic and equidimensional pyrite microcrystals with a light sulfur isotope composition.Multiple lines of evidence indicate Qingjiangonema was a sulfate-reducing bacterium that exhibits similar patterns of cell organization to filamentous forms within the phylum Desulfobacterota,including the sulfate-reducing Desulfonema and sulfide-oxidizing cable bacteria.Phylogenomic analyses confirm separate,independent origins of multicellularity in Desulfonema and in cable bacteria.Molecular clock analyses infer that the Desulfobacterota,which encompass a majority of sulfate-reducing taxa,diverged~2.41 billion years ago during the Paleoproterozoic Great Oxygenation Event,while cable bacteria diverged~0.56 billion years ago during or immediately after the Neoproterozoic Oxygenation Event.Taken together,we interpret Qingjiangonema as a multicellular sulfate-reducing microfossil and propose that cable bacteria evolved from a multicellular filamentous sulfate-reducing ancestor.We infer that the diversification of the Desulfobacterota and the origin of cable bacteria may have been responses to oxygenation events in Earth’s history.
基于人类对全球环境造成重大影响的事实,诺贝尔奖得主克鲁岑(Paul Crutzen)与生态学家斯托默(Eugene Stoermer)于2000年在前人研究基础上提出了人类世(Anthropocene)的概念.2016年,在南非的国际地质大会中,国际人类世工作组建议将人类世确定为全新世之后的一个新地质年代单元.作为一个新的地质时代,人类世的地质环境显著不同于全新世,人类活动对地球系统的影响在某种程度上相当于甚至超过了自然营力的作用.当前,人类世工作组正在遴选全球标准界线层型剖面和点位(Global boundary Stratotype Section and Point, GSSP)以及辅助层型剖面,以正式确定人类世的起始时间.
