Bacterial SSU rRNA Research Articles

Post-transcriptional modifications in the small subunit ribosomal RNA from Thermotoga maritima, including presence of a novel modified cytidine

Post-transcriptional modifications of RNA are nearly ubiquitous in the principal RNAs involved in translation. However, in the case of rRNA the functional roles of modification are far less established than for tRNA, and are subject to less knowledge in terms of specific nucleoside identities and their sequence locations. Post-transcriptional modifications have been studied in the SSU rRNA from Thermotoga maritima (optimal growth 80 degrees C), one of the most deeply branched organisms in the Eubacterial phylogenetic tree. A total of 10 different modified nucleosides were found, the greatest number reported for bacterial SSU rRNA, occupying a net of approximately 14 sequence sites, compared with a similar number of sites recently reported for Thermus thermophilus and 11 for Escherichia coli. The relatively large number of modifications in Thermotoga offers modest support for the notion that thermophile rRNAs are more extensively modified than those from mesophiles. Seven of the Thermotoga modified sites are identical (location and identity) to those in E. coli. An unusual derivative of cytidine was found, designated N-330 (Mr 330.117), and was sequenced to position 1404 in the decoding region of the rRNA. It was unexpectedly found to be identical to an earlier reported nucleoside of unknown structure at the same location in the SSU RNA of the archaeal mesophile Haloferax volcanii.

Rates of ribosomal RNA evolution are uniquely accelerated in eukaryotes.

A novel procedure for testing the relative rates of evolution is described. The procedure, the distance-matrix rate test, consists of creating a graph that displays two complete distance matrices for two different genes derived from the same group of species, an approach made practical by numerous whole genomic sequences. The results in this paper show that the molecular clock of ribosomal RNA from Eukaryotes is uniquely accelerated and highly variable while those of Archaea and Bacteria are not. This idiosyncratic eukaryotic rRNA evolution is not observed with four different protein genes. The distance matrix rate test consists of plotting the distance of one gene (from two different species) against the distance of a second gene (from the same pair of species) in the form of a simple X-Y plot. Because it is not possible to compute variances (or co-variances in this case) that can be meaningfully compared to expectations from a Poisson process, the test does not permit calculations of an index of dispersion. In place of this, equations are given for the 95% confidence limits expected for a Poisson process. The test was applied to the proteins rpsl1 and rp114, as one example, and to rps11 and ssu rRNA as a second example. In addition, the cytochrome c and cytochrome c oxidase evolution from a larger group of Eukaryotes are compared to each other and that of the ssu rRNA. This graphical test shows that the evolution of the four proteins and the archael and bacterial ssu rRNA's are consistent with a Poisson process since last common ancestor. The distance-matrix rate test that is introduced in this study needs to make no assumptions regarding evolutionary rates, divergence times, or phylogenetic relationships.

Successional Changes in an Evolving Anaerobic Chlorophenol-Degrading Community Used To Infer Relationships between Population Structure and System-Level Processes

The response of a complex methanogenic sediment community to 2-chlorophenol (2-CP) was evaluated by monitoring the concentrations of this model contaminant and important metabolic intermediates and products and by using rRNA-targeted probes to track several microbial populations. Key relationships between the evolving population structure, formation of metabolic intermediates, and contaminant mineralization were identified. The nature of these relationships was intrinsically linked to the metabolism of benzoate, an intermediate that transiently accumulated during the mineralization of 2-CP. Before the onset of benzoate fermentation, reductive dehalogenation of 2-CP competed with methanogenesis for endogenous reducing equivalents. This suppressed H(2) levels, methane production, and archaeal small-subunit (SSU)-rRNA concentrations in the sediment community. The concentrations of bacterial SSU rRNA, including SSU rRNA derived from "Desulfovibrionaceae" populations, tracked with 2-CP levels, presumably reflecting changes in the activity of dehalogenating organisms. After the onset of benzoate fermentation, the abundance of Syntrophus-like SSU rRNA increased, presumably because these syntrophic organisms fermented benzoate to methanogenic substrates. Consequently, although the parent substrate 2-CP served as an electron acceptor, cleavage of its aromatic nucleus also influenced the sediment community by releasing the electron donors H(2) and acetate. Increased methane production and archaeal SSU-rRNA levels, which tracked with the Syntrophus-like SSU-rRNA concentrations, revealed that methanogenic populations in particular benefited from the input of reducing equivalents derived from 2-CP.

Phylogenetic diversity of ultraplankton plastid small-subunit rRNA genes recovered in environmental nucleic acid samples from the Pacific and Atlantic coasts of the United States.

The scope of marine phytoplankton diversity is uncertain in many respects because, like bacteria, these organisms sometimes lack defining morphological characteristics and can be a challenge to grow in culture. Here, we report the recovery of phylogenetically diverse plastid small-subunit (SSU) rRNA gene (rDNA) clones from natural plankton populations collected in the Pacific Ocean off the mouth of Yaquina Bay, Oreg. (OCS clones), and from the eastern continental shelf of the United States off Cape Hatteras, N.C. (OM clones). SSU rRNA gene clone libraries were prepared by amplifying rDNAs from nucleic acids isolated from plankton samples and cloning them into plasmid vectors. The PCR primers used for amplification reactions were designed to be specific for bacterial SSU rRNA genes; however, plastid genes have a common phylogenetic origin with bacteria and were common in both SSU rRNA gene clone libraries. A combination of restriction fragment length polymorphism analyses, nucleic acid sequencing, and taxon-specific oligonucleotide probe hybridizations revealed that 54 of the 116 OCS gene clones were of plastid origin. Collectively, clones from the OCS and OM libraries formed at least eight unique lineages within the plastid radiation, including gene lineages related to the classes Bacillariophyceae, Cryptophyceae, Prymnesiophyceae, Chrysophyceae, and Prasinophyceae; for a number of unique clones, no close phylogenetic neighbors could be identified with confidence. Only a group of two OCS rRNA gene clones showed close identity to the plastid SSU rRNA gene sequence of a cultured organism [Emiliania huxleyi (Lohmann) Hay and Mohler; 99.8% similar]. The remaining clones could not be identified to the genus or species level. Although cryptic species are not as prevalent among phytoplankton as they are among their bacterial counterparts, this genetic survey nonetheless uncovered significant new information about phytoplankton diversity.

A computer-simulated restriction fragment length polymorphism analysis of bacterial small-subunit rRNA genes: efficacy of selected tetrameric restriction enzymes for studies of microbial diversity in nature.

An assessment of 10 tetrameric restriction enzymes (TREs) was conducted by using a computer-simulated restriction fragment length polymorphism (RFLP) analysis for over 100 proximally and distally related bacterial small-subunit (SSU) rRNA gene sequences. Screening SSU rDNA clone libraries with TREs has become an effective strategy because of logistic simplicity, commercial availability, and economy. However, the rationale for selecting the type and number of TREs has not been systematically evaluated. Our objective was to identify the optimal combination of TREs for RFLP screening of cloned SSU rRNA genes from undefined bacterial clone libraries. After computer-simulated TRE digestion, the resultant fragments were categorized on the basis of the frequency of different restriction fragment size classes. Three groups of distribution patterns for the TREs were determined and further examined via graphical exploratory data analysis. The RFLP size-frequency distribution data for each group of enzymes were then used to infer phylogenetic relationships via the neighbor-joining method. The resulting bootstrap values and the correct placement of node bifurcations were used as additional criteria to evaluate the efficacy of the selected TREs. These RFLP data were compared with known phylogenetic relationships based on SSU rRNA sequence analysis as defined by the Ribosomal Database Project. A heuristic approach testing random combinations of TREs showed that three or more TRE combinations detected > 99% of the operational taxonomic units (OTUs) within the model data set. OTUs that remained undetected after three TRE treatments had a median sequence similarity of 96.1%. Of the 10 restriction enzymes examined, HhaI, RsaI, and BstUI (group 3) were the most efficacious at detecting and differentiating bacterial SSU rRNA genes on the basis of their ability to correctly classify OTUs. Group 3 TREs are therefore recommended for screening in studies using bacterial SSU rRNA genes as descriptors of in situ microbial diversity.