The role of microbes and biofilms in leaf fossilization

化石是通过一系列复杂的生物、化学和地质过程形成的。植物的部分，如树叶，通常是碳化的，对于木材，通常是硅化的。在对动物身体的研究中，已经表明细菌产生的生物膜可以在软组织的石化中发挥作用。通过生物膜，软组织结构可以被精确地保存下来。带负电荷的生物膜表面有利于生物膜中矿物质的沉淀。在第一个资助期，B3项目以小龙虾为重点调查了节肢动物的节肢动物习性。小龙虾中的碳酸钙在两天后就会析出。微生物组分析证明，小龙虾的定植是由一系列细菌种群组成的，这些细菌种群的需氧量不断下降。优势菌属是具有侵略性的产生蛋白酶、几丁质酶和脂肪酶的细菌属。在较高的温度下，它们会导致小龙虾迅速腐烂，即使在没有氧气的情况下也是如此；在较低的温度下，这一过程的速度会大大降低。与动物的生物膜不同，微生物生物膜在化石树叶挤压的发生中所起的作用鲜为人知。只有几项研究表明，树叶生物膜可以形成，也可以结合矿物质。矿化生物膜可能对食草动物和机械损伤具有保护作用。在第2685号研究小组的框架内，将在C3项目中研究这种生物膜在自然环境和水族馆中的形成情况。在项目C4中，将阐明生物膜形成背后的复杂过程，包括哪些条件以及哪些细菌或真菌可以导致矿物沉淀或叶片组织的降解。为此，将从生物膜中分离出细菌和真菌的个别菌株。将这些微生物一起或单独与树叶在无菌实验室条件下培养，并分析它们对树叶保存或腐烂的影响。一旦生物膜形成，就会测试细菌进行哪些离子浓度或哪些代谢过程(释放磷酸盐、分解尿素、氧化铁)，作为在叶子上沉淀矿物质的先决条件。我们从第一个资助期的结果也表明，微生物的腐烂活动必须停止或减缓，才能继续石化。这可能发生在沉积物中沉积后，推测是通过在缺氧条件下细菌产生的酸释放出重金属。为此，将在实验室研究重金属对生物膜的影响，以开发叶片石化早期阶段的机制模型。

Fossils are formed through a complex series of biological, chemical, and geological processes. Plant parts such as leaves are commonly carbonized, or in the case of wood, silicified. In studies on animal carcasses, it has been shown that biofilms produced by bacteria can play a role in the fossilization of soft tissues. Through biofilms, soft-tissue structures can be preserved in exact detail. The negatively charged surface of a biofilm facilitates the precipitation of minerals in the biofilm. In the first funding period, Project B3 investigated the taphonomy of arthropods with a focus on crayfish. Precipitation of calcium carbonate in the crayfish can occur after only two days. Microbiome analysis documented that colonization of the crayfish consisted of a succession of bacterial populations with continuously decreasing oxygen demand. Dominant were bacterial genera that are aggressive producers of proteases, chitinases, and lipases. At higher temperatures, they led to the rapid decay of the crayfish, even in the absence of oxygen; at lower temperatures, the rate of the process was strongly reduced. In contrast to biofilms in animals, the role of microbial biofilms in the genesis of fossil leaf compressions is poorly known. It has been shown in only a few studies that leaf biofilms can form and also incorporate minerals. A mineralized biofilm may have a protective function against herbivores and mechanical damage. Within the framework of Research Unit 2685, the formation of such biofilms in natural settings and in aquaria will be studied in Project C3. In Project C4, the complex processes behind biofilm formation will be elucidated, including which conditions and which bacteria or fungi can lead to mineral precipitation or to the degradation of leaf tissues. To this end, individual strains of bacterial and fungal species will be isolated from the biofilms. Together or alone, these microbes will be incubated with leaves under sterile laboratory conditions, and their influence on the leaf preservation or decay will be analyzed. As soon as a biofilm has been formed, it will be tested which ion concentrations or which metabolic processes (release of phosphate, breakdown of urea, oxidation of iron) are carried out by the bacteria as a prerequisite for the precipitation of minerals on the leaves. Our results from the first funding period have also shown that the decay activity of microorganisms must be stopped or slowed down so that fossilization can continue. This may happen after deposition in sediment, presumably through the release of heavy metals from the acid produced by bacteria in anoxic conditions. For this reason, the effect of heavy metals on biofilms will be investigated in the laboratory to develop a mechanistic model of an early phase of leaf fossilization.