Tiny Mys­tery Plas­mid

Note­wor­thy

Maybe it's be­cause we have a soft spot for plas­mids here at STC. Or maybe it's be­cause its se­quence has been known since 1995 but its abun­dance and preva­lence were not rec­og­nized un­til now. But we find this tiny 2‑gene plas­mid, pBI143, re­mark­able.

From the study's graph­i­cal ab­stract. Source. 

Yes, pBI143 was first se­quenced in 1995. Orig­i­nally, it was de­scribed sim­ply as "a Bac­teroides plas­mid." Its gene struc­ture is strik­ingly sim­ple. One gene en­codes a repli­ca­tion pro­tein; a sec­ond gene en­codes a pro­tein that func­tions to mo­bi­lize the plas­mid when co-ex­ist­ing with a con­juga­tive plas­mid. Sur­pris­ingly, a 2024 pa­per de­scribes this tiny plas­mid as among the most nu­mer­ous ge­netic el­e­ments in the hu­man gut. Its 2.7 kb se­quence makes up over 0.1% of gut metage­nomic reads! More­over, it is found in more than 90% of in­di­vid­u­als in the in­dus­tri­al­ized coun­tries sur­veyed. What is this lit­tle crea­ture do­ing? That is not clear at all. For now, pBI143 just seems to be self­ishly hang­ing around, per­haps cost­ing the host some loss of fit­ness, i.e., a par­a­site. Though in some cases, it ac­quires some ad­di­tional genes. But there's still much to be learned from this tiny cir­cle of DNA!