- negative ▁b acter ia ▁such ▁as ▁Sal mon ella , ▁Sh ig ella , ▁Y ers in ia , ▁V ib rio , ▁it ▁is ▁used ▁for ▁inject ing ▁to xic ▁prote ins ▁into ▁e uk ary otic ▁cells . ▁For ▁its ▁structure , ▁it ▁is ▁often ▁described ▁as ▁inject is om es ▁or ▁need le ▁and ▁s yr inge - like ▁appar atus . ▁Disc over ed ▁from ▁Y ers in ia ▁p est is , ▁it ▁was ▁found ▁that ▁T 3 SS ▁can ▁inject ed ▁to x ins ▁directly ▁from ▁the ▁b acter ial ▁cy top las m ▁into ▁the ▁cy top las m ▁of ▁its ▁host ' s ▁cells . ▁ ▁Type ▁IV ▁▁ ▁Type ▁IV ▁secret ion ▁system ▁( T 4 SS ▁or ▁T F SS ) ▁is ▁related ▁to ▁b acter ial ▁conjug ation ▁system , ▁by ▁which ▁different ▁b acter ia ▁can ▁exchange ▁their ▁D N As . ▁The ▁particip ating ▁b acter ia ▁can ▁be ▁of ▁the ▁same ▁or ▁different ▁Gram - negative ▁b acter ial ▁species . ▁It ▁can ▁transport ▁single ▁prote ins , ▁as ▁well ▁as ▁protein - prote in ▁and ▁DNA - prote in ▁complex es . ▁Secret ion ▁is ▁transferred ▁directly ▁from ▁the ▁recip ient ▁cell ▁through ▁the ▁cell ▁memb ran es . ▁Ag rob acter ium ▁tum ef aci ens , ▁from ▁which ▁it ▁was ▁originally ▁discovered , ▁uses ▁this ▁system ▁to ▁send ▁the ▁T - D NA ▁portion ▁of ▁the ▁Ti ▁pl as mid ▁into ▁ ▁plant ▁cells ,