Characterization of an Obligate Intracellular Bacterium in the Midgut Epithelium of the Bulrush Bug Chilacis typhae (Heteroptera, Lygaeidae, Artheneinae)
ABSTRACT
Many members of the suborder Heteroptera have symbiotic bacteria, which are usually found extracellularly in specific sacs or tubular outgrowths of the midgut or intracellularly in mycetomes. In this study, we describe the second molecular characterization of a symbiotic bacterium in a monophagous, seed-sucking stink bug of the family Lygaeidae (sensu stricto).
Chilacis typhae
possesses at the end of the first section of the midgut a structure which is composed of circularly arranged, strongly enlarged midgut epithelial cells. It is filled with an intracellular endosymbiont. This “mycetocytic belt” might represent an evolutionarily intermediate stage of the usual symbiotic structures found in stink bugs. Phylogenetic analysis based on the 16S rRNA and the
groEL
genes showed that the bacterium belongs to the
Gammaproteobacteria
, and it revealed a phylogenetic relationship with a secondary bacterial endosymbiont of
Cimex lectularius
and free-living plant pathogens such as
Pectobacterium
and
Dickeya
. The distribution and ultrastructure of the rod-shaped
Chilacis
endosymbiont were studied in adults and nymph stages using fluorescence
in situ
hybridization (FISH) and electron microscopy. The detection of symbionts at the anterior poles of developing eggs indicates that endosymbionts are transmitted vertically. A new genus and species name, “
Candidatus
Rohrkolberia cinguli,” is proposed for this newly characterized clade of symbiotic bacteria.