Functions of symbiotic fungus gardens in higher termites of the genus Macrotermes: evidence against the acquired enzyme hypothesis.

Behavioural, microbiological and biochemical studies on Macrotermes subhyalinus and M. michaelseni by collaborating laboratories in the U.K., Switzerland and Australia are described. Younger workers consume both primary forage and the conidia of a symbiotically associated fungus of the genus Termitomyces, but all workers produce a fully competent cellulase complex (endoglucanase + glucosidase) in the midgut which is clearly distinguishable from analogous enzymes in fungal tissues. Workers have a RQ of 1.0; although a bacterial flora is present, assessments of CH4/H2 efflux and intestinal VFAs suggest that respiration is sustained by aerobic carbohydrate dissimilation. Calculations based on estimates of food ingestion by workers and measurements of cellulase activity show that endogenous production of reducing sugars from polysaccharide is sufficient to sustain the observed metabolic rate. Conidia contain both cellulase and glucose at much higher concentrations than other fungal tissues, but the role and fate of these substances on entering the young worker guts is unknown. Older workers consume fully composted forage in which cellulose, hemicellulose, pectin and lignin are all significantly degraded, with a corresponding increase in nitrogen content.