Anaerobic metabolism in the leech (Hirudo medicinalis L.): direct and indirect calorimetry during severe hypoxia

Stratified bacterial community in the bladder of the medicinal leech, Hirudo verbana

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 alpha-Proteobacteria (Ochrobactrum symbiont), beta-Proteobacteria (Beta-1 and Beta-2 symbionts), delta-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 beta-proteobacterial cells. These results clearly demonstrate that a simple but organized microbial community exists in the bladder of the medicinal leech.

Succinate and alanine as anaerobic end-products in the diving turtle (Chrysemys picta bellii)

The western painted turtle is an extremely anoxia-tolerant vertebrate capable of tolerating blood lactate levels of 150-200 mM. Since lactate increases to such high levels, other fermentation end-products such as succinate and alanine, which have not been previously measured in this species, might also be expected to increase. Therefore, I measured turtle heart, liver, and blood concentrations of lactate, succinate, and alanine following a 28-day anoxic dive at 5 degrees C. Succinate and lactate concentrations increased significantly in all three compartments while alanine increased significantly in the liver only. Lactate was found to accumulate by a similar amount in all three compartments (66.4-80.5 micromol g or ml(-1) in the blood compartment) and was used as a reference to which alanine and succinate concentrations could be compared. Succinate and alanine levels increased by 2 and 0.9% of lactate in liver, approximately 0.3 and 0.04% of lactate in blood, and 0.6 and 0.07% of lactate in heart, respectively. The contribution of each to the total anoxic heat production was calculated and accounted for an additional 1.5% of the previously measured exothermic gap. I conclude that succinate and alanine concentrations do increase in the anoxic turtle but are minor anaerobic end-products.