Intracolony variation of bacterial gut microbiota among castes and ages in the fungus‐growing termite Macrotermes gilvus

Abstract

The fungus-growing termites Macrotermes cultivate the obligate ectosymbiontic fungi, Termitomyces. While their relationship has been extesively studied, little is known about the gut bacterial symbionts, which also presumably play a crucial role for the nutrition of the termite host. In this study, we investigated the bacterial gut microbiota in two colonies of Macrotermes gilvus, and compared the diversity and community structure of bacteria among nine termite morphotypes, differing in caste and/or age, using terminal restriction fragment length polymorphism (T-RFLP) and clonal analysis of 16S rRNA. The obtained molecular community profiles clustered by termite morphotype rather than by colony, and the clustering pattern was clearly more related to a difference in age than to caste. Thus, we suggest that the bacterial gut microbiota change in relation to the food of the termite, which comprises fallen leaves and the fungus nodules of Termitomyces in young workers, and leaves degraded by the fungi, in old workers. Despite these intracolony variations in bacterial gut microbiota, their T-RFLP profiles formed a distinct cluster against those of the fungus garden, adjacent soil and guts of sympatric wood-feeding termites, implying a consistency and uniqueness of gut microbiota in M. gilvus. Since many bacterial phylotypes from M. gilvus formed monophyletic clusters with those from distantly related termite species, we suggest that gut bacteria have co-evolved with the termite host and form a microbiota specific to a termite taxonomic and/or feeding group, and furthermore, to caste and age within a termite species.

Diversity and Genomes of Uncultured Microbial Symbionts in the Termite Gut

“…4) In the guts of termites examined thus far, one of three anaerobic bacterial groups, the genus Treponema in Spirochaetes, the order Bacteroidales in Bacteroidetes, and the class Clostridia in Firmicutes, predominated, followed by the other two. 7,8,22,24,27,28) Occasionally, the candidate class ''Endomicrobia'' in the phylum Elusimicrobia (originally designated the candidate phylum Termite Group 1) 20,34) was also found as a dominant group in the guts of lower termites, 7,22) and the candidate phylum TG3 (Termite Group 3) and the phylum Fibrobacteres were the second most dominant groups in the guts of wood-feeding higher termites. 7,27) In summary, distinct termite species harbor different bacterial species with community structures specific to the host species, but most of those bacteria belong to phylogenetic clusters that are unique to termites and shared among diverse termite species.…”

“…Although these bacteria have not strictly co-speciated with their termite hosts, their phylogeny loosely reflects the host taxonomic positions, and the bacterial microbiota is consistent within a host species or genus. 7,8) This suggests that the majority of termite gut bacteria are not allochthonous but autochthonous symbionts, vertically transmitted from parents to offspring via proctodeal trophallaxis (i.e., transmission of the gut contents from the anus of a donor to the mouth of a recipient). 4) In the guts of termites examined thus far, one of three anaerobic bacterial groups, the genus Treponema in Spirochaetes, the order Bacteroidales in Bacteroidetes, and the class Clostridia in Firmicutes, predominated, followed by the other two.…”

“…Approximately 10 6 to 10 8 prokaryotic cells are present in a single gut. [6][7][8][9] The majority are bacteria, and archaea account only for 0 to 10%. 10,11) The most frequently found archaea are methanogens.…”

“…In both lower and higher termites, it has been estimated that a single termite species harbors several hundred or more gut bacterial phylotypes. 7,8,22,29,33) The phylotypes have been classified into 24 phylum-level clusters (Fig. 2), and they form one or more monophyletic clusters in each bacterial phylum.…”

“…The taxonomic compositions of gut bacteria have been examined in various termite species by 16S rRNA clone analysis (Table 1). 7,8,[20][21][22][23][24][25][26][27][28][29][30][31][32] More than 1,500 phylotypes in total (with a criterion of >97% sequence identity in near-full length 16S sequence) have been obtained to date, most of which have never been detected in other environments and show low sequence similarities to cultured bacterial strains. In both lower and higher termites, it has been estimated that a single termite species harbors several hundred or more gut bacterial phylotypes.…”