Stratified bacterial community in the bladder of the medicinal leech, Hirudo verbana
Article first published online: 12 AUG 2009
© 2009 Society for Applied Microbiology and Blackwell Publishing Ltd
Volume 11, Issue 10, pages 2758–2770, October 2009
How to Cite
Kikuchi, Y., Bomar, L. and Graf, J. (2009), Stratified bacterial community in the bladder of the medicinal leech, Hirudo verbana. Environmental Microbiology, 11: 2758–2770. doi: 10.1111/j.1462-2920.2009.02004.x
- Issue published online: 2 OCT 2009
- Article first published online: 12 AUG 2009
- Received 17 December, 2008; accepted 10 June, 2009.
Most animals harbour symbiotic microorganisms inside their body, where intimate interactions occur between the partners. The medicinal leech, Hirudo verbana, possesses 17 pairs of excretory bladders that harbour a large number of intracellular and extracellular symbiotic bacteria. In this study, we characterized the bladder symbionts using molecular phylogenetic analyses, transmission electron microscopy (TEM) and fluorescence in situ hybridization (FISH). Restriction fragment length polymorphism (RFLP) and sequence analyses of 16S rRNA gene clone libraries suggested that six bacterial species co-colonize the leech bladders. Phylogenetic analyses revealed that these species belong to the α-Proteobacteria (Ochrobactrum symbiont), β-Proteobacteria (Beta-1 and Beta-2 symbionts), δ-Proteobacteria (Bdellovibrio symbiont) and Bacteroidetes (Niabella and Sphingobacterium symbionts). Species-specific PCR detection and FISH confirmed the localization of the symbiotic bacteria in the bladders. The Ochrobactrum, Beta-1, Bdellovibrio and Sphingobacterium symbionts were consistently detected in 13 leeches from two populations, while infection rate of the other symbionts ranged between 20% and 100% in the two leech populations. Transmission electron microscopy observations of the bladders revealed epithelial cells harbouring a number of intracellular bacilli and an additional type of extracellular, rod-shaped bacteria in the luminal region. Fluorescence in situ hybridization with group-specific oligonucleotide probes revealed the spatial organization of the bacterial species in the bladder: the Ochrobactrum symbiont was located intracellularly inside epithelial cells; the Bacteroidetes were localized close to the epithelium in the lumen of the bladder; and the Bacteroidetes layer was covered with dense β-proteobacterial cells. These results clearly demonstrate that a simple but organized microbial community exists in the bladder of the medicinal leech.