There are trillions of microbes found throughout the human body and they exceed the number of eukaryotic cells by 10-fold. Metagenomic studies have revealed that the majority of these microbes are found within the gut, playing an important role in the host's digestion and nutrition. The complexity of the animal digestive tract, unculturable microbes, and the lack of genetic tools for most culturable microbes make it challenging to explore the nature of these microbial interactions within this niche. The medicinal leech, Hirudo verbana, has been shown to be a useful tool in overcoming these challenges, due to the simplicity of the microbiome and the availability of genetic tools for one of the two dominant gut symbionts, Aeromonas veronii. In this study, we utilize 16S rRNA gene pyrosequencing to further explore the microbial composition of the leech digestive tract, confirming the dominance of two taxa, the Rikenella-like bacterium and A. veronii. The deep sequencing approach revealed the presence of additional members of the microbial community that suggests the presence of a moderately complex microbial community with a richness of 36 taxa. The presence of a Proteus strain as a newly identified resident in the leech crop was confirmed using fluorescence in situ hybridization (FISH). The metagenome of this community was also pyrosequenced and the contigs were binned into the following taxonomic groups: Rikenella-like (3.1 MB), Aeromonas (4.5 MB), Proteus (2.9 MB), Clostridium (1.8 MB), Eryspelothrix (0.96 MB), Desulfovibrio (0.14 MB), and Fusobacterium (0.27 MB). Functional analyses on the leech gut symbionts were explored using the metagenomic data and MG-RAST. A comparison of the COG and KEGG categories of the leech gut metagenome to that of other animal digestive-tract microbiomes revealed that the leech digestive tract had a similar metabolic potential to the human digestive tract, supporting the usefulness of this system as a model for studying digestive-tract microbiomes. This study lays the foundation for more detailed metatranscriptomic studies and the investigation of symbiont population dynamics.
Keywords: high-throughput sequencing, beneficial microbes, symbiosis, medicinal leech
Citation: Maltz MA, Bomar L, Lapierre P, Morrison HG, McClure EA, Sogin ML and Graf J (2014) Metagenomic analysis of the medicinal leech gut microbiota. Front. Microbiol. 5:151. doi: 10.3389/fmicb.2014.00151
Received: 28 November 2013; Accepted: 21 March 2014;
Published online: 17 April 2014.
Edited by:Ute Hentschel, University of Wuerzburg, Germany
Reviewed by:Seana Kelyn Davidson, University of Washington, USA
Copyright © 2014 Maltz, Bomar, Lapierre, Morrison, McClure, Sogin and Graf. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) or licensor are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.
*Correspondence: Joerg Graf, Department of Molecular and Cell Biology, University of Connecticut, 91 N Eagleville Rd, Storrs CT 06269, USA e-mail: firstname.lastname@example.org
†Present address: Lindsey Bomar, The Forsyth Institute, Cambridge, USA; Pascal Lapierre, New York State Department of Health, Albany, USA