The impact of bacterial activity on decay and fossilization of arthropods: An experimental approach

节肢动物是后生动物中生物多样性最高的。对节肢动物进化和生殖的认识主要来自所谓的保护矿床（Konservatlagerstätten）中保存完好的化石。这些化石是由生物体死亡后立即开始的一系列复杂的生物，化学和地质过程形成的。在死亡和尸体嵌入沉积物之间，腐烂（需氧）或/和腐败（厌氧）-由源自节肢动物肠道植物群和/或其环境的微生物催化-可能导致部分丧失对系统发育解释很重要的特征。这种细菌的腐烂在不同组织中的速度并不一样，导致了对脊椎动物化石记录的严重误解，因为部分分解的生物化石被错误地分类。除了生物体的腐烂之外，细菌也被证明有助于化石的形成，通过合成生物膜，生物膜随后通过矿物沉淀和产生尸体的坚硬和精细组织的铸件或假形态而被破坏。此外，矿物的沉淀可能是细菌活动的产物。本项目的总体目标是在节肢动物微生物活动的背景下提高对腐烂过程的一般理解。为此，我们将开始监测整个节肢动物的肢解，并描述随着时间的推移，尸体上的微生物群落的发展。衰变监测的目标不仅是观察物理分离，而且要了解化学和物理参数的影响，并确定矿化的最佳条件。不同环境条件下腐烂节肢动物的微生物组将通过16 S rRNA测序进行表征，并与其来源（肠道，环境），腐烂速度和形态变化相关。另一方面，将从腐烂的尸体中分离以产生生物膜和胞外酶为特征的细菌菌株并进行表征。为了证明或反驳生物膜的形成有利于化石形成的假设，另一方面，胞外酶的分泌导致加速降解，不同组织类型的节肢动物将在项目的第二部分与分离的细菌菌株一起孵育。将记录衰变或再结晶，并系统地了解细菌活性对再结晶过程的影响。因此，最后的实验应有助于更好地了解的条件，确定发生异常保存节肢动物在不同的环境设置通过地质时间。

Arthopods represent the highest biodiversity among metazoa. Insights into evolution and phylogeny of arthropods are mainly derived from exceptionally well-preserved fossils from so called conservation deposits (Konservatlagerstätten). These fossils were formed by a complex sequence of biological, chemical and geological processes that starts immediately after the death of the organism. Between the death and the embedding of the carcass into the sediment, decay (aerobic) or/and putrefaction (anaerobic)- catalyzed by microorganisms that originate from the gut flora of the arthropod and/or its environment – may lead to a partial loss of characteristic features that are important for phylogenetic interpretations. This bacterial decay, which is not equally fast in different tissues, has led to serious misinterpretation in the fossil record of vertebrates, because fossils of partially decomposed organisms were incorrectly classified. In addition to the decay of organisms, bacteria have also been shown to contribute to the formation of fossils, by synthesizing biofilms which later fossilize by precipitation of minerals and yield casts or pseudomorphs of the hard and fine tissues of the carcass. Also the precipitation of minerals may be a product of bacterial activity.The overall goal of this project is to improve the general understanding of decay processes in the context with microbial activity in arthropods. To this end we will start monitoring the disarticulation of whole arthropods and characterize the developing microbial communities on the carcass over the time. The goal of the decay monitoring will not only be to observe the physical disarticulation, but also to understand the influence of chemical and physical parameters and to identify the best conditions for mineralization. The microbiome of decaying arthropods under different environmental conditions will be characterized by 16S rRNA sequencing and correlated to its sources (gut, environment), the speed of the decay and morphological changes. On the other hand, bacterial strains which are characterized by the production of biofilms and exoenzymes will be isolated from the decaying cadavers and characterized. To prove or disprove the hypotheses that the formation of biofilms favors the formation of fossils, and that on the other hand the secretion of exoenzymes, however, leads to an accelerated degradation, different tissue types of arthropods will be incubated with the isolated bacterial strains in the second part of the project. Decay or fossilisation will be recorded and yield systematic insights into the influence of bacterial activity on the fossilisation process. Thus, finally the experiments shall contribute to a better understanding of the conditions that determine the occurrence of exceptional preservation of arthropods in different environmental settings through geological time.