Metatranscriptomic Analysis of the Bacterial Symbiont Dactylopiibacterium carminicum from the Carmine Cochineal Dactylopius coccus (Hemiptera: Coccoidea: Dactylopiidae)

Abstract

The scale insect <i>Dactylopius coccus</i> produces high amounts of carminic acid, which has historically been used as a pigment by pre-Hispanic American cultures. Nowadays carmine is found in food, cosmetics, and textiles. Metagenomic approaches revealed that <i>Dactylopius</i> spp. cochineals contain two <i>Wolbachia</i> strains, a betaproteobacterium named <i>Candidatus</i> Dactylopiibacterium carminicum and <i>Spiroplasma</i>, in addition to different fungi. We describe here a transcriptomic analysis indicating that <i>Dactylopiibacterium</i> is metabolically active inside the insect host, and estimate that there are over twice as many <i>Dactylopiibacterium</i> cells in the hemolymph than in the gut, with even fewer in the ovary. Albeit scarce, the transcripts in the ovaries support the presence of <i>Dactylopiibacterium</i> in this tissue and a vertical mode of transmission. In the cochineal, <i>Dactylopiibacterium</i> may catabolize plant polysaccharides, and be active in carbon and nitrogen provisioning through its degradative activity and by fixing nitrogen. In most insects, nitrogen-fixing bacteria are found in the gut, but in this study they are shown to occur in the hemolymph, probably delivering essential amino acids and riboflavin to the host from nitrogen substrates derived from nitrogen fixation.