show Abstracthide AbstractBarbulanympha is a unicellular eukaryotic (protist) symbiont that digests lignocellulose in the hindgut of the wood-eating cockroach, Cryptocercus punctulatus. In addition to being symbiotic with its insect host, Barbulanympha is itself host to thousands of Bacteroidales bacterial symbionts attached to its cell surface. Single cells of Barbulanympha were isolated and genomic sequences of the ectosymbionts were obtained to understand the evolution of ectosymbiosis, especially in comparison to endosymbiosis. The ectosymbiont genome was also used to investigate the role of nitrogen in driving the symbiosis with Barbulanympha and C. punctulatus.