Preliminary Study on Bacterial Traits Associated with the Behavioural Responses of Metarhabditis rainai (Nematoda: Rhabditidae) in the Ginger Rhizosphere

Interactions between soil bacteria and free-living bacterivorous nematodes influence nutrient cycling, microbial community dynamics, and rhizosphere processes, yet the behavioural responses of nematodes to bacterial traits remain poorly understood. This study investigated the relationship between bacterial phenotypic traits and the behavioural responses of Metarhabditis rainai isolated from ginger rhizosphere soil in Limpopo Province, South Africa. Three bacterial isolates (Stenotrophomonas chelatiphaga, Bacillus sp., and Aeromonas sp.) were characterized for hemolytic activity, motility, biofilm formation, and gentamicin susceptibility. Molecular analyses of 18S and 16S rDNA confirmed the identities of the nematode and bacterial isolates. Nematode attraction was evaluated using an in vitro feeding preference assay. Significant effects of bacterial isolate, time, and their interaction were detected (p < 0.0001), indicating distinct behavioural responses among treatments. Aeromonas sp. elicited the strongest attraction, followed by Bacillus sp., whereas S. chelatiphaga induced a weaker response. Bacterial phenotypic traits varied among isolates, with Bacillus sp. exhibiting the highest hemolytic activity, motility, and gentamicin resistance. Overall, M. rainai displayed selective attraction toward different bacterial isolates, and these responses coincided with variation in bacterial traits. However, no direct causal relationship between individual bacterial traits and nematode behaviour was established.