IDENTIFICATION AND CO-OCCURRENCE OF DEFENSE SYSTEMS IN THE Shewanella PANGENOME

SANHUEZA SALAS, LUIS FRANCISCO; CERBINO GABRIELA N.; AYALA NUÑEZ, TEOLINCACIHUATL; RAMIREZ, MARIA SOLEDAD

Chapadmalal

Congreso; XVIII CONGRESO DE LA SAMIGE 2023; 2023

Defense systems (DS) protect bacteria against the attack of mobile genetic elements,such as phages and plasmids, ensuring their survival. In recent years, a wide variety of newDS have been discovered expanding considerably the current knowledge in the field. Theanalysis of their genetic localization revealed that they can be grouped in the same regionof a genome forming defense islands or hotspots. The aim of this work was to identify theDS in the Shewanella genus, a non-fermenting gram-negative rod that thrives in aquaticniches and causes infections in humans. In addition, we evaluated whether there was anassociation between DS and the host habitat. Complete and draft Shewanella spp.genomes available from Genbank until July 2023 were included in the analysis (n= 431). Allgenomes were organized based on their average nucleotide identity (ANI) value usingFastANI and visualized using the rplot command from RStudio. Information regarding thesource of isolation was also included in the analysis. DS families were identified using thetool PADLOC v1.1.0., and potential defense hotspots were detected by comparativegenome analysis using Mauve v2 and ACT v18.1.0 tools. We detected 98 DS familiesdistributed heterogeneously throughout all species. The most frequent familiescorresponded to restriction-modification (RM) (645), DMS (DNA modification systems; 274),dXTPases (218) and CRISPR-Cas (220). We also observed that some DS families werehighly diversified within this genus, i.e., CRISPR-Cas (10 subtypes), Abi (abortive infectionsystem; 14), and Retron (a reverse transcriptase-based system; 11). On the other hand,some DS showed a considerable occurrence within individual species, such as Abi (29),CBASS (22), Gabija (22,) and Retron (21) in Shewanella algae; Abi (56), Mokosh (29),SoFic (29) and Lamassu (25) in Shewanella baltica; and Abi (34), Mokosh (33), SoFic (29)and CBASS (18) in Shewanella xiamenensis; showing a few differences at species level.Colocalization and comparative analyses revealed that some DS coexist in a specifichotspot, as seen for the clinical isolate Shewanella sp. Shew256, which contained twoputative defense islands. The first one. harboring the systems type-I RM with AbiD and thesecond one with systems SoFic, type-V RM and DMS. Similarly, the environmental isolateS. frigidimarina Ag06-30 encoded a type-I RM, a DMS, and Zorya systems at the samehotspot, which reveals the plasticity of each defense island. Lastly, we observed that mostMokosh and SoFic systems were found frequently in aquatic and animal-related hosts,which corresponded mainly to S. baltica and S. xiamenensis isolates, but sporadically inclinical isolates (predominantly S. algae). Our analysis reveals that Shewanella spp. adaptsto the environment by acquiring and employing several DS systems. This adaptation isprobably shaped by the encounter between each host and the foreign mobile elementspresent in an ecosystem.