Lund, Marie Braad1; Schätzle, Sarah3; Schramm, Andreas5; Kjeldsen, Kasper Urup6
1 Department of Biological Sciences, Microbiology, Faculty of Science, Aarhus University, Aarhus University2 Department of Bioscience - Microbiology, Department of Bioscience, Science and Technology, Aarhus University3 Department of Bioscience - Microbiology, Aarhus University4 Department of Bioscience - Center for Geomicrobiology, Department of Bioscience, Science and Technology, Aarhus University5 Department of Bioscience - Microbiology, Department of Bioscience, Science and Technology, Aarhus University6 Department of Bioscience - Center for Geomicrobiology, Department of Bioscience, Science and Technology, Aarhus University
Clone library-based studies have shown that almost all lumbricid earthworm species harbour host-specific symbiotic bacteria belonging to the novel genus Verminephrobacter in their nephridia (excretory organs). To date the only described representative from this genus is Verminephrobacter eiseniae, the specific symbiont of the earthworm Eisenia fetida. In this study two novel rod-shaped, non-endosporeforming, betaproteobacterial symbionts were isolated from the nephridia of two closely related earthworm species. Both isolates were affiliated with the genus Verminephrobacter by 16S rRNA gene sequence analysis. Similarly to V. eiseniae, the two isolates grew aerobically with a preference for low oxygen concentrations on a range of sugars, fatty acids and amino acids and fermentatively on glucose and pyruvate. These phenotypes match well with the conditions reported or inferred for the nephridial environment. Based on 16S rRNA gene similarity,DNA–DNA hybridization value and phenotypic characteristics the two isolates are clearly distinct from V. eiseniae. Phenotypic characteristics could not clearly differentiate the two strains as separate species but a low DNA–DNA hybridization value of 57.3%, their earthworm host specificity, differing temperature ranges and pH optima suggest that they represent two subspecies of a novel species of Verminephrobacter. For this species, the name V. aporrectodeae sp. nov. is proposed, with the two subspecies V. aporrectodeae subsp. tuberculatae (type strain, At4T = DSM 21361T = LMG 25313T) and V. aporrectodeae subsp. caliginosae (type strain, Ac9T = DSM 21895T = LMG 5312T) isolated from the nephridia of the earthworms Aporrectodea tuberculata and A. caliginosa, respectively.