Digestion, diet and polyethism in two fungus-growing termites: Macrotermes subhyalinus Rambur and M. michaelseni Sjøstedt

Abstract

Cellulase and its component activities, endo-β-1,4-glucanase and β-1,4-glucosidase, were measured in the guts of larvae, minor soldiers and the four categories of workers (young and old minor and young and old major) in Macrotermes michaelseni and M. subhyalinus. These activities were also measured in fungal material associated with colonies of both species. Substantial activity cellulase (18.2–28.1 μg glucose/termite/h) and its component activities were found in all four worker categories of M. michaelseni with 80% less activity in the minor soldiers and none in the larvae. There was a similar distribution of cellulase activity among the castes of M. subhyalinus. At least 90% of the cellulase activity in major workers of M. michaelseni was found in the midgut. The only fungal material associated with either species with significant enzyme activity were the fungal nodules (cellulase activity, 8.22 ± 0.86 and 4.34 ± 0.24 μg glucose/mg wet wt for M. michaelseni and M. subhyalinus, respectively). The cellulases from major workers and fungal nodules from M. michaelseni were partially resolved by gel chromatography. Endo-β-1,4-glucanases and β-1,4-glucosidases from both cellulases were multi-component with different elution profiles on Bio-Gel ® P60 chromatography. Glucose and cellobiose were present throughout the gut of M. michaelseni. No other reducing sugars were present. Reducing sugars were found in all fungal material associated with M. michaelseni. In the nodules the only reducing sugar was glucose (184 ± 83 nmol/mg dry wt). Old fungal comb contained glucose, cellobiose, xylose, arabinose and galacturonic acid (13 ± 3, 5 ± 3, 15 ± 8, 24 ± 3, 12 ± 3 nmol/mg dry wt, respectively). Fresh and ripe fungal comb contained smaller amounts of the same sugars. The RQ values for young and old major workers of M. michaelseni were 0.999 ± 0.007 (SD; n = 4) and 1.002 ± 0.005 (SD; n = 5), respectively. Oxygen was consumed by the two categories at rates of 180 and 230 nmol/termite/h.