[P004] Poster

1:00 PM - 1:50 PM JST(4:00 AM - 4:50 AM UTC)

[P02-232] Application of the hitchhiking phenomenon—transport of non-motile pollutant-degrading bacteria by motile bacteria—for bioremediation

○Tae Ito¹, Hanako Matuzoe¹, Hiromi Kato¹, Stari Leonardo¹, Kouhei Kishida¹, Yoshiyuki Otsubo¹, Yuji Nagata¹ (1. Tohoku University (Japan))

Keywords:

Hitchhiking motility,Paenibacillus,γ-HCH

The organochlorine insecticide γ-hexachlorocyclohexane (γ-HCH) remains an important environmental pollutant, even though its use has been essentially prohibited, and it is designated as a persistent organic pollutant (POP). We are investigating γ-HCH–degrading bacteria with the aim of applying them to bioremediation. However, their practical use is often limited by poor motility and restricted dispersal in soil. We previously demonstrated that the γ-HCH–degrading bacterium Sphingobium japonicum strain UT26, which is nearly non-motile on solid media, can disperse by being transported by the highly motile Paenibacillus sp. NK-L2, a phenomenon referred to as “hitchhiking.” In this study, we investigated the factors affecting hitchhiking motility and evaluated its potential application in bioremediation. UT26 and NK-L2 were mixed at defined ratios and spotted onto agar plates under various nutrient and agar conditions. Colony expansion was monitored over time, and the spreading area of UT26 was quantified using image analysis. Hitchhiking was reproducibly observed on nutrient-rich YT medium, particularly on 2×YT agar at a concentration of 2.0%, providing a robust experimental platform for systematic analysis of this phenomenon and its underlying mechanisms. Surfactin treatment enhanced UT26 dispersal, suggesting that surfactin-mediated swarming plays a key role in hitchhiking. In contrast, sporulated driver cells did not exhibit hitchhiking, indicating that the physiological state of the driver strain influences hitchhiking efficiency. Notably, hitchhiking was observed even in the presence of ampicillin (Ap), under conditions in which the Ap-susceptible NK-L2 survives by transporting the Ap-degrading UT26, suggesting a mutualistic interaction between the two strains. To assess strain specificity, we tested combinations of nine Paenibacillus strains and ten non-motile bacterial strains. Hitchhiking was not observed in all combinations, indicating that the driver–hitchhiker relationship is strain-specific and governed by biological interactions rather than simple physical attachment. Furthermore, hitchhiking preferentially occurred in combinations in which the driver strain did not inhibit the growth of the hitchhiker, suggesting that growth inhibition is a key determinant of hitchhiking specificity. Taken together, our results demonstrate that hitchhiking is a reproducible and regulated phenomenon influenced by environmental conditions, swarming motility, and interspecies interactions. These findings provide new insights into microbial interactions and contribute to the development of strategies to improve bioremediation efficiency.