Bacteriocytes

Bacteriocytes are specialized host cells that house intracellular symbiotic bacteria. They are found in a range of invertebrates but are especially well studied in insects. In many phloem-feeding insects, bacteriocytes cluster into a distinct organ called the bacteriome, often located in the abdomen.

The best-known example is in aphids, which harbor the bacterium Buchnera aphidicola in their bacteriocytes. Buchnera provides essential amino acids and other nutrients that are scarce in the aphid diet, enabling the insect to thrive on phloem sap. The symbiont's genome is highly reduced and depends on the host for many cellular functions.

Bacteriocytes generally contain the primary endosymbiont and may also host secondary symbionts. The relationship is usually obligate, with vertical transmission from mother to offspring; during reproduction, bacteriocytes or their symbionts are passed to developing eggs, ensuring the newborn retains the symbiosis. The relationship is tightly integrated, with host cells enabling symbiont survival and transfer, and symbionts contributing nutrients and metabolic capabilities.

Impact and significance: Bacteriocytes illustrate coevolution of host and symbiont, genome reduction, and nutritional mutualism. They are of interest in evolutionary biology and agriculture due to aphid biology and pest management considerations.