Investigation of candidate division TM7, a recently recognized major lineage of the domain Bacteria with no known pure-culture representatives.
A molecular approach was used to investigate a recently described candidate division of the domain Bacteria, TM7, currently known only from environmental 16S ribosomal DNA sequence data. A number of TM7-specific primers and probes were designed and evaluated. Fluorescence in situ hybridization (FISH) of a laboratory scale bioreactor using two independent TM7-specific probes revealed a conspicuous sheathed-filament morphotype, fortuitously enriched in the reactor. Morphologically, the filament matched the description of the Eikelboom morphotype 0041-0675 widely associated with bulking problems in activated-sludge wastewater treatment systems. Transmission electron microscopy of the bioreactor sludge demonstrated that the sheathed-filament morphotype had a typical gram-positive cell envelope ultrastructure. Therefore, TM7 is only the third bacterial lineage recognized to have gram-positive representatives. TM7-specific FISH analysis of two full-scale wastewater treatment plant sludges, including the one used to seed the laboratory scale reactor, indicated the presence of a number of morphotypes, including sheathed filaments. TM7-specific PCR clone libraries prepared from the two full-scale sludges yielded 23 novel TM7 sequences. Three subdivisions could be defined based on these data and publicly available sequences. Environmental sequence data and TM7-specific FISH analysis indicate that members of the TM7 division are present in a variety of terrestrial, aquatic, and clinical habitats. A highly atypical base substitution (Escherichia coli position 912; C to U) for bacterial 16S rRNAs was present in almost all TM7 sequences, suggesting that TM7 bacteria, like Archaea, may be streptomycin resistant at the ribosome level.
Hugenholtz
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P
Advanced Wastewater Management Centre, Department of Microbiology and Parasitology, The University of Queensland, Brisbane 4072, Australia. philiph@biosci.uq.edu.au
Tyson
G W
GW
Webb
R I
RI
Wagner
A M
AM
Blackall
L L
LL
D019149:Bioreactors; D003470:Culture Media; D017931:DNA Primers; D004275:DNA, Ribosomal / Q000032:analysis / Q000235:genetics; D004783:Environmental Microbiology; D006094:Gram-Positive Bacteria / Q000145:classification* / Q000235:genetics / Q000254:growth & development; D017404:In Situ Hybridization, Fluorescence; D008854:Microscopy, Electron; D008969:Molecular Sequence Data; D010802:Phylogeny; D012336:RNA, Ribosomal, 16S / Q000235:genetics; D017422:Sequence Analysis, DNA; D012722:Sewage / Q000382:microbiology
D003470:Culture Media; D017931:DNA Primers; D004275:DNA, Ribosomal; D012336:RNA, Ribosomal, 16S; D012722:Sewage