Morphological, biochemical, and molecular characterization of the root-knot nematode Meloidogyne spartinae and assessment of bacterial assemblages in infected smooth cordgrass roots

Smooth cordgrass (Spartina alterniflora), a keystone species in marine ecosystems is crucial for maintaining the health and stability of coastal habitats. However, the cordgrass root-knot nematode (Meloidogyne spartinae), has been reported infecting this plant and still very little is known about this plant-parasitic nematode species well adapted to coastal saltmarsh. Morphological, biochemical, molecular, and gall microbiome analyses were performed using three M. spartinae populations to better characterized this nematode. M. spartinae females did not produce egg masses; females, eggs and males are found inside of the root galls. No esterase activity was detected using homogenates of one, five or ten females of M. spartinae per well regardless of the population. Nevertheless, one strong band of malate dehydrogenase activity (MDH = N1b phenotype) was detected using macerate of one female. Partial 18S rRNA, the D2-D3 expansion segments of 28S rRNA, partial COI and NAD5 gene sequences were obtained. The phylogenetical analyses showed that M. spartinae was related to M. marylandi and M. graminis. Microbiome analysis of cordgrass root galls revealed Proteobacteria as the most abundant phylum and Vibrio as the most abundant genus, in addition other environmentally important bacterial genera, such as those with nitrogen fixation and sulfate reducing roles. Our findings provide novel information on the bacterial assemblages of cordgrass infected roots and demonstrated via rRNA and mtDNA gene sequences that M. spartinae is clearly different from all other Meloidogyne spp.