Costly symbiont inheritance

Abstract

Symbiosis Long-established microbial symbioses tend toward genome erosion and increasing host dependence. Some relationships are so pivotal to host survival that maintaining a stable partnership is crucial. Koga et al. have investigated the stable inheritance of an insect bacterial gut symbiont called Ishikawaella between generations of its Plataspidae stinkbug hosts. Ishikawaella has a highly reduced genome yet provides essential amino acids for the bug. The bugs lay eggs in rows on plants, and capsules holding symbionts are deposited among the eggs. The capsule also contains a combination of a specialist insect protein the authors identified as posterior midgut dominant protein (PMDP) and a symbiont-derived chaperone molecule, GroEL. Together, these molecules protect the delicate Ishikawaella for the 7 to 10 days it takes for the eggs to hatch, at which point the young bugs feed on the capsule to obtain the vital symbionts. However, the production of PMDP shortens the life of the female bugs, which is the price a mother pays to ensure inheritance. Proc. Natl. Acad. Sci. U.S.A. 118 , e2103957118 (2021).