Differential enumeration and in situ localization of microorganisms in the hindgut of the lower termite Mastotermes darwiniensis by hybridization with rRNA-targeted probes |
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Authors: | M Berchtold A Chatzinotas W Schönhuber A Brune R Amann D Hahn H König |
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Institution: | Institut fur Mikrobiologie und Weinforschung, Johannes Gutenberg-Universitat, Becherweg 15, D-55099 Mainz, Germany. |
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Abstract: | We examined the abundance and spatial distribution of major phylogenetic groups of the domain Bacteria in hindguts of the
Australian lower termite Mastotermes darwiniensis by using in situ hybridization with group-specific, fluorescently labeled, rRNA-targeted oligonucleotide probes. Between
32.0 ± 7.2% and 52.3 ± 8.2% of the DAPI-stained cells in different hindgut fractions were detected with probe EUB338, specific
for members of the domain Bacteria. About 85% of the prokaryotic cells were associated with the flagellates of the thin-walled
anterior region (P3a) and the thick wall of the posterior region (P3b/P4) of the hindgut, as shown by DAPI staining. At most,
half of the EUB338-detected cells hybridized with one of the other probes that targeted a smaller assemblage within the bacterial
domain. In most fractions, cells were found in varying numbers with probe ALF1b, which targeted members of the α-Proteobacteria,
whereas substantial amounts of sulfate-reducing bacteria, gram-positive bacteria with a high DNA G+C content and members of
the Cytophaga-Flavobacterium cluster of the Cytophaga-Flavobacterium-Bacteroides (CFB) phylum could be detected only in the wall fraction of P3b/P4. This clearly indicates that the hindgut microhabitats
differ in the composition of their microbial community. In situ hybridization of cryosections through the hindgut showed only
low numbers of bacteria attached to the P3a wall. In contrast, the wall of P3b was densely colonized by rod- and coccus-shaped
bacteria, which could be assigned to the Cytophaga-Flavobacterium cluster of the CFB phylum and to the group of gram-positive bacteria with a high DNA G+C content, respectively. Oxygen concentration
profiles determined with microelectrodes revealed steep oxygen gradients both in P3a and P3b. Oxygen was consumed within 100
μm below the gut surface, and anoxic conditions prevailed in the central portions of both gut regions, indicating that oxygen
consumption in the hindgut does not depend on the presence of a biofilm on the hindgut wall.
Received: 17 May 1999 / Accepted: 16 September 1999 |
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Keywords: | Freeze sectioning Fluorescent ?oligonucleotide probes In situ hybridization Intestinal microorganisms Mastotermes darwiniensis Oxygen microsensors rRNA Termites |
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