In vitro Trypanocidal Activity, Genomic Analysis of Isolates, and in vivo Transcription of Type VI Secretion System of Serratia marcescens Belonging to the Microbiota of Rhodnius prolixus Digestive Tract

is a bacterium with the ability to colonize several niches, including some eukaryotic hosts. have been recently found in the gut of hematophagous insects that act as parasite vectors, such as , and . While some strains have been reported as symbiotic or pathogenic to other insects, the role of populations from the gut microbiota of , a vector of Chagas' disease, remains unknown. Bacterial colonies from gut were isolated on BHI agar. After BOX-PCR fingerprinting, the genomic sequences of two isolates RPA1 and RPH1 were compared to others from the NCBI database in other to estimate their evolutionary divergence. The trypanolytic activity of these two bacterial isolates against (DM28c clone and Y strain) was assessed by microscopy. In addition, the gene expression of type VI secretion system (T6SS) was detected by RT-PCR. Comparative genomics of RPA1 and RPH1 revealed, besides plasmid presence and genomic islands, genes related to motility, attachment, and quorum sensing in both genomes while genes for urea hydrolysis and type II secretion system (T2SS) were found only in the RPA1 genome. The trypanolytic activity of both strains was stronger in their stationary phases of growth than in their exponential ones, with 65-70 and 85-90% of epimastigotes (Dm28c clone and Y strain, respectively) being lysed after incubation with RPA1 or RPH1 in stationary phase. Although T6SS transcripts were detected in guts up to 40 days after feeding (DAF), morbidity or mortality did not appear to be affected. In this report, we made available two trypanolytic strains from gut to the scientific community together with their genomic sequences. Here, we describe their genomic features with the purpose of bringing new insights into the adaptations for colonization of the specific niche of triatomine guts. This study provides the basis for a better understanding of the role of in the microbiota of gut as a potential antagonist of in this complex system.