Differences between bacterial communities in the gut of a soil-feeding termite (Cubitermes niokoloensis) and its mounds

Abstract

In tropical ecosystems, termite mound soils constitute an important soil compartment covering around 10% of African soils. Previous studies have shown (S. Fall, S. Nazaret, J. L. Chotte, and A. Brauman, Microb. Ecol. 28:191-199, 2004) that the bacterial genetic structure of the mounds of soil-feeding termites (Cubitermes niokoloensis) is different from that of their surrounding soil. The aim of this study was to characterize the specificity of bacterial communities within mounds with respect to the digestive and soil origins of the mound. We have compared the bacterial community structures of a termite mound, termite gut sections, and surrounding soil using PCR-denaturing gradient gel electrophoresis (DGGE) analysis and cloning and sequencing of PCR-amplified 16S rRNA gene fragments. DGGE analysis revealed a drastic difference between the genetic structures of the bacterial communities of the termite gut and the mound. Analysis of 266 clones, including 54 from excised bands, revealed a high level of diversity in each biota investigated. The soil-feeding termite mound was dominated by the Actinobacteria phylum, whereas the Firmicutes and Proteobacteria phyla dominate the gut sections of termites and the surrounding soil, respectively. Phylogenetic analyses revealed a distinct clustering of Actinobacteria phylotypes between the mound and the surrounding soil. The Actinobacteria clones of the termite mound were diverse, distributed among 10 distinct families, and like those in the termite gut environment lightly dominated by the Nocardioidaceae family. Our findings confirmed that the soil-feeding termite mound (C. niokoloensis) represents a specific bacterial habitat in the tropics.

FIG. 1.

Schematics of gut and mound of soil-feeding termites showing the various environments sampled. AG, anterior gut; MG, midgut. Anatomic gut segments: C, crop; M, midgut; P1 to P5, proctodeal segments 1 to 5, respectively.

FIG. 2.

DGGE profiles of bacterial 16S rRNA genes amplified from gut and mound environments of soil-feeding termites (Cubitermes niokoloensis) and dendrogram of DGGE profile similarities. The numbers on profiles indicate the bands that were cloned and sequenced. Band richness is marked in the circles. AG, anterior gut; MG, midgut; PG, posterior gut; FM, fresh mound; Gal, gallery; AMG, cluster of anterior and midgut profiles; PWG, cluster of posterior and whole gut profiles.

FIG. 3.

Rarefaction curve of bacterial 16S rRNA gene clones recovered from the gut, mound of soil-feeding termites (Cubitermes niokoloensis), and surrounding savanna soil. The expected number of phylotypes was calculated from the number of clones, with inclusion in the same species based on 97% sequence similarity. The three compartments studied are represented as follows: squares, whole gut; crosses, IW; and circles, surrounding savanna soil.

FIG. 4.

Relative clone frequencies in major phylogenetic groups of the clone libraries from the gut of soil-feeding termites (Cubitermes niokoloensis), mound of soil-feeding termites, and SS. The various subphyla of Proteobacteria are indicated by Greek letters. WG, whole termite gut.

FIG. 5.

Subtree of actinomycetes from the complete tree (1,578 species; 2005 database) of the 16S rRNA database in the ARB package showing the phylogenetic positions of 40 phylotypes from a soil-feeding termite mound (IW), termite gut, and SS. The numbers of clones in each phylotype (97% sequence similarity) are given in parentheses. The quick add marked species feature of ARB (parsimony) was used to position our sequences, and the position was manually corrected using the neighboring species found with NCBI BLAST. Nodes with bootstrap values of >70% and between 50 and 69% are marked with black and empty circles, respectively. The scale bar indicates an approximately 10% difference in nucleotide sequence. posit, positive.