Symbiotic Bacterial Diversity, Functional Profiling and Antibiotic Susceptibility of the Red Imported Fire Ant.

The red imported fire ant (RIFA), Solenopsis invicta, is a globally invasive pest that causes substantial ecological, agricultural, and public health challenges. Conventional control strategies primarily depend on chemical insecticides, which present environmental risks and limited long-term efficacy. In this study, we comprehensively investigated the bacterial microbiota of S. invicta and compared it with a sympatric non-target ant species (Pheidole nodus) to explore the ecological significance and biocontrol potential of symbiotic bacteria. High-throughput 16S rRNA sequencing revealed that the symbiotic bacterial community of S. invicta exhibited markedly higher richness and diversity. A total of 1651 amplified sequence variants (ASVs) were identified, of which 1089 ASVs are unique to the RIFAs, and 460 are unique to non-target ants. Linear discriminant analysis effect size (LEfSe) highlighted 33 biomarker taxa (score > 6.5), with strong enrichment of Stenotrophomonas, Serratia, Pseudomonas, Luteibacter, Bradyrhizobium, Brucella, Smaragdicoccus, Gordonia, and Aeromonas. Functional predictions and enzymatic assays in vitro demonstrated that dominant cultivable genera, particularly Stenotrophomonas (SI-7, SI-17), Serratia (SI-1, SI-3, SI-6, SI-18), and Pseudomonas (SI-2, SI-8, SI-9, SI-11, SI-19), exhibit substantial proteolytic and lipolytic activity, suggesting key roles in nutrient metabolism and host ecological adaptability. Antibiotic susceptibility profiling further revealed that florfenicol shows broad-spectrum inhibitory activity against these dominant symbionts. These findings indicate that disrupting dominant symbiotic bacteria may impair host physiology and thus serve as a targeted control strategy. Overall, the study elucidates the diversity, functional potential, and biocontrol applicability of the S. invicta microbiome, providing a foundation for developing sustainable, microbiome-based pest management approaches.