ARS | Publication request: 'candidatus Paenicardinium Endoi', An Endosymbiont of the Plant-Parasitic Nematode Heterodera Glycines (Nemata: Tylenchida), Affiliated to the Phylum Bacteriodetes

Submitted to: International Journal of Systematic and Evolutionary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 14, 2005
Publication Date: July 1, 2006
Citation: Noel, G.R., Atibalentja, N. 2006. 'Candidatus paenicardinium endoi', an endosymbiont of the plant-parasitic nematode heterodera glycines (Nemata: Tylenchida), affiliated to the phylum bacteriodetes. International Journal Systematic Evolutionary Microbiology. 56:1697-1702.

Interpretive Summary: Soybean cyst nematode (SCN) is an important yield limiting pest of soybean in all production areas of the US. Estimated annual crop loss ranges from $240 million to $1.4 billion. One area of research to control SCN that has received limited effort is biological control. This paper reports the discovery of a new genus and species of bacterium that infects SCN internally and can only complete its life cycle inside the nematode. Very few nematode species of widely divergent taxonomic groups contain internal bacteria. The bacterium in soybean cyst nematode is unique among plant-parasitic nematodes and is distantly related and evolutionarily older than a similar group of bacteria that infect insects. In insects the bacteria interrupt reproduction. Although this has not yet been studied for the bacterium that attacks SCN, eggs and sperms of some nematodes were highly infected with this new bacterium. Thus, if production of viable eggs is reduced, the bacterium will have great promise as a new biological control organism for SCN.

Technical Abstract: During TEM studies of females of the plant-parasitic nematodes Globodera rostochiensis and Heterodera goettingiana and juveniles of H. glycines conducted in the 1970s, bacteria-like endosymbionts were observed. These organisms were characterized as being rod-shaped ranging in size from 0.3 " 0.5 um in diameter X 1.8 " 3 um in length and containing structures labeled as striated inclusion bodies or tubular structures. We obtained a population of H. glycines from the original soybean field in order to conduct TEM studies of females and males and to determine the phylogenetic relationships of the 16S rRNA and gyrB genes. The bacterium was observed in the pseudocoelom and intestine of juveniles, females, and males and in oocytes and spermatozoa. The bacterium was polymorphic, measuring 0.4 " 0.8 X 2.5 " 4.5 um, and many specimens contained an array of microfilaments similar to those observed in 'Candidatus Cardinium hertigii', the endosymbiont of Encarsia spp. wasps. Phylogenetic analysis of the 16S rRNA and gyrB genes of the H. glycines-infecting bacterium revealed a 93% and 81% sequence similarity, respectively to the 16S rRNA and gyrB genes of 'Candidatus C. hertigii'. Thus, a new taxon, 'Candidatus Paenicardinium endoi'is proposed for the bacterial endosymbiont of the plant-parasitic nematode, Heterodera glycines.