Zoological Institute, Department of Molecular Evolutionary Biology, University of Hamburg, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany.
Can J Microbiol. 2009 Nov;55(11):1250-60. doi: 10.1139/w09-085.
Intracellular bacterial symbionts are known from various insect groups, particularly from those feeding on unbalanced diets, where the bacteria provide essential nutrients to the host. In the case of reed beetles (Coleoptera: Chrysomelidae, Donaciinae), however, the endosymbionts appear to be associated with specialized "glands" that secrete a material used for the beetles' unusual water-tight cocoon. These glands were discovered over a century ago, but the bacteria they contain have yet to be characterized and placed in a phylogenetic context. Here, we describe the ultrastructure of two endosymbiotic species ("Candidatus Macropleicola appendiculatae" and "Candidatus Macropleicola muticae") that reside in cells of the Malpighian tubules of the reed beetle species Macroplea appendiculata and Macroplea mutica, respectively. Fluorescent in situ hybridization using oligonucleotides targeting the 16S rRNA gene specific to Macroplea symbionts verified the localization of the symbionts in these organs. Phylogenetic analysis of 16S rRNA placed "Candidatus Macropleicola" in a clade of typically endosymbiotic Enterobacteriaceae (gamma-proteobacteria). Finally, we discuss the evidence available for the hypothesis that the beetle larvae use a secretion produced by the bacteria for the formation of an underwater cocoon.
细胞内细菌共生体存在于各种昆虫群体中，特别是那些以不平衡饮食为食的昆虫，在这些昆虫中，细菌为宿主提供必需的营养。然而，在 reed beetles（鞘翅目：叶甲科，Donaciinae）中，内共生体似乎与专门的“腺体”有关，这些腺体分泌一种用于甲虫特殊的防水茧的物质。这些腺体在一个多世纪前就被发现了，但它们所包含的细菌尚未被描述并置于系统发育背景中。在这里，我们描述了分别存在于 reed beetle 物种 Macroplea appendiculata 和 Macroplea mutica 的 Malpighian 小管细胞中的两种内共生物种（“Candidatus Macropleicola appendiculatae”和“Candidatus Macropleicola muticae”）的超微结构。使用针对 Macroplea 共生体的 16S rRNA 基因的寡核苷酸进行荧光原位杂交验证了共生体在这些器官中的定位。16S rRNA 的系统发育分析将“Candidatus Macropleicola”置于典型内共生肠杆菌科（γ-变形菌）的一个分支中。最后，我们讨论了幼虫使用细菌产生的分泌物形成水下茧的假说的现有证据。
