Department of Biology, Indiana University, Bloomington, IN 47405, USA.
Evol Dev. 2013 Jul-Aug;15(4):243-56. doi: 10.1111/ede.12028. Epub 2013 May 14.
Fossils of soft tissues provide important records of early animals and embryos, and there is substantial evidence for a role for microbes in soft tissue fossilization. We are investigating the initial events in interactions of bacteria with freshly dead tissue, using marine embryos as a model system. We previously found that microbial invasion can stabilize embryo tissue that would otherwise disintegrate in hours or days by generating a bacterial pseudomorph, a three dimensional biofilm that both replaces the tissue and replicates its morphology. In this study, we sampled seawater at different times and places near Sydney, Australia, and determined the range and frequency of different taphonomic outcomes. Although destruction was most common, bacteria in 35% of seawater samples yielded morphology‐preserving biofilms. We could replicate the taphonomic pathways seen with seawater bacterial communities using single cultured strains of marine gammaproteobacteria. Each given species reproducibly generated a consistent taphonomic outcome and we identified species that yielded each of the distinct pathways produced by seawater bacterial communities. Once formed,bacterial pseudomorphs are stable for over a year and resist attack by other bacteria and destruction by proteases and other lytic enzymes. Competition studies showed that the initial action of a pseudomorphing strain can be blocked by a strain that destroys tissues. Thus embryo preservation in nature may depend on contingent interactions among bacterial species that determine if pseudomorphing occurs.We used Artemia nauplius larvae to show that bacterial biofilm replacement of tissue is not restricted to embryos, but is relevant for preservation of small multicellular organisms. We present a model for bacterial self‐assembly of large‐scale three‐dimensional tissue pseudomorphs, based on smallscaleinteractions among individual bacterial cells to form local biofilms at structural boundaries within the tissue. Localbiofilms then conjoin to generate the pseudomorph.
软组织化石为早期动物和胚胎提供了重要记录，并且有大量证据表明微生物在软组织化石形成中起作用。我们正在研究细菌与刚死亡组织相互作用的初始事件，使用海洋胚胎作为模型系统。我们之前发现，微生物的入侵可以通过生成细菌拟晶（一种三维生物膜，既能替代组织，又能复制其形态）来稳定组织，否则组织会在数小时或数天内解体。在这项研究中，我们在澳大利亚悉尼附近的不同时间和地点采集了海水样本，并确定了不同化石化结果的范围和频率。尽管破坏是最常见的，但在 35%的海水中，细菌产生了形态保存的生物膜。我们可以使用单一培养的海洋γ变形菌来复制在海水中细菌群落中看到的化石化途径。每个给定的物种都能重现一致的化石化结果，我们确定了产生海水细菌群落产生的不同途径的物种。一旦形成，细菌拟晶可以稳定超过一年，并且可以抵抗其他细菌的攻击和蛋白酶和其他溶酶的破坏。竞争研究表明，一个拟晶形成菌株的初始作用可以被破坏组织的菌株所阻断。因此，自然界中胚胎的保存可能取决于细菌物种之间的 contingent 相互作用，这些相互作用决定了是否会发生拟晶形成。我们使用卤虫无节幼体来表明细菌生物膜对组织的替代作用不仅限于胚胎，而且与小多细胞生物的保存有关。我们提出了一个基于单个细菌细胞之间的小尺度相互作用形成组织内结构边界处局部生物膜的细菌自组装大规模三维组织拟晶的模型。然后，局部生物膜连接在一起形成拟晶。
