How firebrats (Thysanura: Lepismatidae) detect and nutritionally benefit from their microbial symbionts Enterobacter...

The phylogenetically ancient firebrats, Thermobia domestica (Packard) (Thysanura: Lepismatidae), lack any form of long-distance communication, yet are able to locate mates in sustained hot and humid microhabitats, typically within human habitations where they feed on dried goods, including cellulosic substrates. We have recently shown that firebrats aggregate in response to two symbiotic microorganisms in their feces, the bacterium Enterobacter cloacae and the fungus Mycotypha microspora. Our objectives were to determine how firebrats detect M. microspora and E. cloacae, and whether these microbial symbionts nutritionally benefit firebrats. Applied to a glass surface in bioassays, E. cloacae as well as the isolated exopolysaccharide of E. cloacae induced arrestment of firebrats, whereas M. microspora induced arrestment only in the presence of cellulosic substrate. When M. microspora and E. cloacae were grown aerobically on cellulose agar, only M. microspora yielded zones of clearing indicative of enzymatic cellulose degradation. Firebrats also arrested in response to d-glucose, which is a constituent of the exopolysaccharide and which is produced by the cellulase of M. microspora during cellulose degradation. First- to third-instar nymphs of firebrats that were fed E. cloacae, M. microspora, or a nutrient-rich diet developed equally well. By consuming E. cloacae and M. microspora, and by spreading them through feces, firebrats appear able to occupy nutrient-poor habitats that otherwise would not support development of their offspring.