Castelli Michele, Petroni Giulio
Department of Biology and Biotechnology, University of Pavia, Pavia, Italy.
Department of Biology, University of Pisa, Pisa, Italy.
Microb Ecol. 2025 Mar 14;88(1):15. doi: 10.1007/s00248-025-02509-0.
The order Holosporales is a broad and ancient lineage of bacteria obligatorily associated with eukaryotic hosts, mostly protists. Significantly, this is similar to other evolutionary distinct bacterial lineages (e.g. Rickettsiales and Chlamydiae). Here, we provide a detailed and comprehensive account on the current knowledge on the Holosporales. First, acknowledging the up-to-date phylogenetic reconstructions and recent nomenclatural proposals, we reevaluate their taxonomy, thus re-ranking them as a suborder, i.e. Holosporineae, within the order Rhodospirillales. Then, we examine the phylogenetic diversity of the Holosporineae, presenting the 20 described genera and many yet undescribed sub-lineages, as well as the variety of the respective environments of provenance and hosts, which belong to several different eukaryotic supergroups. Noteworthy representatives of the Holosporineae are the infectious intranuclear Holospora, the host manipulator 'Caedimonas', and the farmed shrimp pathogen 'Candidatus Hepatobacter'. Next, we put these bacteria in the broad context of the whole Holosporineae, by comparing with the available data on the least studied representatives, including genome sequences. Accordingly, we reason on the most probable evolutionary trajectories for host interactions, host specificity, and emergence of potential pathogens in aquaculture and possibly humans, as well as on future research directions to investigate those many open points on the Holosporineae.
全孢菌目是一类广泛且古老的细菌谱系，它们 obligatorily 与真核宿主相关联，主要是原生生物。值得注意的是，这与其他进化上不同的细菌谱系（如立克次氏体目和衣原体）相似。在此，我们提供了关于全孢菌目的当前知识的详细而全面的描述。首先，承认最新的系统发育重建和最近的命名提议，我们重新评估它们的分类，因此将它们重新归类为一个亚目，即全孢菌亚目，隶属于红螺菌目。然后，我们研究全孢菌亚目的系统发育多样性，展示已描述的20个属和许多尚未描述的亚谱系，以及各自来源环境和宿主的多样性，这些宿主属于几个不同的真核超群。全孢菌亚目的显著代表包括感染性的核内全孢菌、宿主操纵者“Caedimonas”以及养殖虾病原体“候选肝杆菌”。接下来，我们通过与关于研究最少的代表（包括基因组序列）的现有数据进行比较，将这些细菌置于整个全孢菌亚目的广泛背景中。因此，我们推断宿主相互作用、宿主特异性以及水产养殖和可能在人类中潜在病原体出现的最可能进化轨迹，以及研究全孢菌亚目众多未解决问题的未来研究方向。 （注：“obligatorily”这个词在文中可能有误，推测原文想表达的是“obligately”，意为“专性地” ）
