Bacteria with nematicidal effects have attracted interest as biocontrol agents of pests and diseases due to their relatively low environmental impact compared to chemical management strategies1. The damage they cause to target nematodes is diverse and imperfectly understood4.
Photorhabdus spp. (Enterobacteriaceae) lives symbiotically within the nematode Heterorhabditis spp. (Rhabditida: Heterorhabditidae). It is known that secondary metabolites of this gram-negative bacterium exhibit insecticidal activity, mainly in Lepidopteran and Coleopteran insects2. Studies have also shown that cell-free culture filtrates of Photorhabdus spp. have nematicidal activity on free-living nematodes and pest phytonematodes; however, the causes of death in these targets are still being studied3.
This works provides information on the effect caused by the intake of Photorhabduslaumondi laumondi (strain LP1900, isolated from Heterorhabditis bacteriophora strain SUP2), in the digestive tract of the bacteriophagous nematode Panagrellusredivivus (Rhabditidae: Panagrolaimidae).
LP1900 strain was cultured on nutrient agar (Difco) plates for 7 days at 29°C (5 repetitions); then 2×103 nematodes were inoculated on each plate, and freely dispersed through the culture. Untreated controls consisted of agar nutrient plates with the 2×103 nematode inoculum alone. Alterations in the posterior esophagus (behind the basal bulb), and in the anterior, middle and posterior intestinal regions of treated nematodes were recorded 24h after treatment under a light microscope (10×) (Eclipse E200; Nikon), and compared with untreated nematodes (Fig. 1).
Nematicidal effect of P. laumondi laumondi LP1900 on the digestive tract of P. redivivus. (A) Both the intestine and the cuticle were intact in untreated nematodes. (B) A rupture in the cuticle near the basal bulb region can be observed on nematodes exposed to a 7-day-old culture of LP1900, spilling the internal contents of the organism. The musculature, from the stoma to the beginning of the basal bulb, showed signs of disintegration. (C, D) A similar effect was observed in the middle and posterior intestinal regions of other treated nematodes.
AS worked with fellowship from Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET). DS and MFA are members of the Research Career of CONICET.
We would like to thank Mariano Maestro for the English revision of the text.
