Role of Microorganisms in the Metabolism of Termites

Abstract

This article reviews the current knowledge of the role of symbiotic microorganisms in the metabolism of termites. The symbiotic microorganisms, comprising bacteria (higher and lower termites) and protozoa (lower termites) are in the hindgut. Cellulose digestion in higher termites appears to be mediated solely by cellulolytic enzymes secreted by the termites. In the lower termites, cellulose is digested by enzymes secreted both by the termites and by the protozoa. The end products of protozoal metabolism (acetate and butyrate) are thought to be used by termites as energy sources. Another method of cellulose digestion is that of the Macrotermitinae which have a symbiotic relationship with fungi of the genus Termitomyces. The termites acquire cellulase from the fungus. The bacteria found in the hindgut are usually facultative even though the hindgut is anaerobic. Some of these bacteria appear to be involved in dinitrogen-fixation in the gut, but do not play any part in cellulose metabolism. Some evidence suggests that termites may be able to re-utilize the nitrogen in the uric acid stores in their fat body using hindgut bacteria. While there is evidence that lignin can be degraded in termite tissues it is difficult to assess the role of the hindgut micro biota in this process. RaIe of Microorganisms in TermiteMetabolism 241

Animal cellulases

“…Removal of intestinal bacteria and protozoa by tetracycline treatments (assumed to eliminate protozoa indirectly by the reduction of bacteria) did not affect cellulase activities in the guts of either species except for a 20 % decrease seen in the hindgut of C. lacteus [53]. To explain the cellulose digestion of higher termites (which make up three-quarters of known termite species [54]), the isolation of cellulolytic bacteria from the gut has been attempted, but only cellulolytic facultative heterotrophs and inherent noncellulolytic spirochetes have been found [18,23]. In N. walkeri and the mound-building higher species N. exitiosus, the majority of the cellulase activity was located in the epithelia and the luminal contents of the midgut [55].…”

“…The presence of symbiotic protozoa or bacteria has been used to explain cellulose digestion in invertebrates and herbivorous cattle. This theory was first proposed by Cleveland, in his work with termites, who demonstrated [16,18]. The intestinal bacteria were proposed as to produce acetate and fix nitrogen to digest cellulose consumed by the host [16,18].…”

“…This theory was first proposed by Cleveland, in his work with termites, who demonstrated [16,18]. The intestinal bacteria were proposed as to produce acetate and fix nitrogen to digest cellulose consumed by the host [16,18]. Later, the focus of research on the digestion of xylophagous insects shifted from inside to outside the digestive tract.…”

“…A high similarity was demonstrated in enzymatic character between one component from the gut and another from the nodules [22]. However, whether such acquired cellulase activity in fungus-growing termites meets the physiological requirements of the hosts is controversial [18,23,24]. Acquisition of digestive enzymes has been explored in other xylophagous arthropods and interpreted as a general phenomenon in xylophagous arthropods including woodwasps, isopods, cerambycid beetles, and attine ants [25].…”

The presence, nature, and role of gut microflora in aquatic invertebrates: A synthesis

“…Many of these studies have focused on the role of the gut microflora of animals whose food quality is poor, either being refractory to digestion or low in essential nutrients such as nitrogen. For example, the gut bacteria of ruminants and termites have been shown to play an important role in cellulose digestion [3,18,52,196], and are also reported to aid in nitrogen acquisition and conservation [27,68,150,162].…”