Wednesday, November 9, 2011

Medicinal leeches, MasterPure RNA Kits, and metatranscriptomics

The overwhelming majority of microorganisms in existence have not been cultured in the laboratory. Even the most abundant and metabolically active members of the microbial community can be challenging to cultivate. Next-generation sequencing is providing insight into the metabolic relationships within microbial communities by sequencing the metatranscriptome.

Bomar et al. report on the gut microbiome of the medicinal leech Hirudo verbena. They found two symbionts in the digestive tract: i) a Rikenella-like bacterium; and ii) Aeromonas veronii. After a blood meal, the largest compartment of the digestive tract (the crop), stores ingested blood for months between feedings. Water and salts are removed from the ingested blood meal, creating a viscous intraluminal fluid (ILF) that contains these symbiotic bacteria. RNA from the ILF was extracted using the MasterPure™ RNA Purification Kit. After mRNA enrichment, an Illumina cDNA library was constructed. Approximatley 81% of the reads mapped to A. veronii or Rikenella. The Rikenella-like bacterium’s transcriptome indicated that energy is obtained by fermenting sugars to acetate. Surprisingly, the Rikenella-like symbiont foraged host mucin glycans rather than the blood meal. Its capacity to use mucins may be important for its ability to survive within the leech gut for up to 6 months between feedings. The discovery of mucin as the primary nutrient enabled the design of a medium that allowed the cultivation of Rikenella under conditions that favored its growth, and pure cultures were obtained. Thus, the application of metatranscriptomics to growing bacteria in diverse habitats can enable the design of media allowing their cultivation.

ResearchBlogging.orgBomar, L, et al. (2011). Directed culturing of microorganisms using metatranscriptomics. mBio, 2 (2) PMID: 21467263

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