by Me­chas — The di­ver­sity of life on earth is not only as­tound­ing but in­un­dated with myr­iad ex­pres­sions of host-sym­biont re­la­tion­ships. Among these, mi­cro­bial sym­bionts are so per­va­sive that they could be con­sid­ered the rule, rather than the ex­cep­tion, among mul­ti­cel­lu­lar eu­kary­otes.