Plasmids may carry genes that provide resistance to naturally occurring antibiotics in a competitive environmental niche, or the proteins produced may act as toxins under similar circumstances, or allow the organism to utilize particular organic compounds that would be advantageous when nutrients are scarce.
Os plásmidos poden portar xenes que proporcionan resistencia a antibióticos presentes de forma natural nun nicho ecolóxico competitivo, ou a proteína producida pode actuar como toxina en circunstancias similares, ou permitir que o organismo utilice un composto orgánico determinado que sería vantaxoso cando escaseasen os nutrientes.