PCR Primer Design for 16S rRNAs for Experimental Horizontal Gene Transfer Test in Escherichia coli

Identification of cellulolytic lactic acid bacteria from the intestines of laying hens given AKBISprob based on 16S ribosomal ribonucleic acid gene analysis

Background and Aim:

Supplementation of AKBISprob (developed in a previous study) in feed can improve production efficiency and poultry health, especially laying hens. In addition, it can also increase cellulolytic lactic acid bacteria (LAB) in chicken intestines, but these bacteria are still unknown; thus, they need to be identified. This study aimed to identify cellulolytic LAB in the intestines of laying hens administered AKBISprob based on 16S ribosomal ribonucleic acid (16S rRNA) gene analysis.

Materials and Methods:

The samples used in this study were 13 LAB isolates from the intestines of laying hens that were given AKBISprob 4%. Cellulolytic LAB DNA was isolated and 16S rRNA gene was amplified by polymerase chain reaction, followed by sequencing, bioinformatics analysis, and phylogenetic tree construction.

Results:

From 10 cellulolytic LAB isolates with a clear zone of >6 mm, four were selected and their DNA was amplified with BaCF and UniB primers ~1500 bp DNA fragments. Of these, the P31H62 isolate was genetically close to Enterococcus hirae strain 1-1X-16 with 92.90% maximum identity, the P33S52 isolate had homology with Enterococcus mundtii strain ZU 26 with 96.76% maximum identity, and the P33S62 isolate was closely related to E. hirae strain SJ3 with 72.96% maximum identity. The phylogenetic tree revealed that the cellulolytic LAB isolates P31H62 and P33S52 were in one cluster closely related to the genus Enterococcus.

Conclusion:

This study suggests that the isolates P31H62, P33S62, and P33S52 from the intestines of laying hens administered 4% AKBISprob are cellulolytic LAB belonging to the genus Enterococcus.

Complete Genome Sequences of Four Parageobacillus Strains Isolated from Soil in Japan

We isolated four Parageobacillus strains from soil in Japan and completely sequenced their genomes. Three of four strains showed ≥98.9% average nucleotide identity (ANI) to Parageobacillus caldoxylosilyticus S1812^T, while one strain, designated KH3-4, showed the highest ANI (91%) to Parageobacillus thermantarcticus M1^T, suggesting the species novelty of KH3-4.

Complete Genome Sequence of Geobacillus sp. Strain E55-1, Isolated from Mine Geyser in Japan

We report here the complete genome sequence of Geobacillus sp. strain E55-1, isolated from the hot sediments of Mine Geyser in Japan. This strain exhibited ∼85% average nucleotide identity and ∼98.5% 16S rRNA sequence identity with the most closely related Geobacillus species.

We report here the complete genome sequence of Geobacillus sp. strain E55-1, isolated from the hot sediments of Mine Geyser in Japan. This strain exhibited ∼85% average nucleotide identity and ∼98.5% 16S rRNA sequence identity with the most closely related Geobacillus species.

Complete Genome Sequence of Pseudomonas otitidis Strain MrB4, Isolated from Lake Biwa in Japan

We isolated Pseudomonas otitidis strain MrB4 from the near-shore area of Lake Biwa in Japan and generated its complete genome sequence. MrB4 possesses a single circular chromosome of 6,089,454 bp, with ∼97% average nucleotide identity to the P. otitidis type strain MCC10330 (draft genome).

We isolated Pseudomonas otitidis strain MrB4 from the near-shore area of Lake Biwa in Japan and generated its complete genome sequence. MrB4 possesses a single circular chromosome of 6,089,454 bp, with ∼97% average nucleotide identity to the P. otitidis type strain MCC10330 (draft genome).

Reconstructing the Phylogeny of Corynebacteriales while Accounting for Horizontal Gene Transfer

Horizontal gene transfer is a common mechanism in Bacteria that has contributed to the genomic content of existing organisms. Traditional methods for estimating bacterial phylogeny, however, assume only vertical inheritance in the evolution of homologous genes, which may result in errors in the estimated phylogenies. We present a new method for estimating bacterial phylogeny that accounts for the presence of genes acquired by horizontal gene transfer between genomes. The method identifies and corrects putative transferred genes in gene families, before applying a gene tree-based summary method to estimate bacterial species trees. The method was applied to estimate the phylogeny of the order Corynebacteriales, which is the largest clade in the phylum Actinobacteria. We report a collection of 14 phylogenetic trees on 360 Corynebacteriales genomes. All estimated trees display each genus as a monophyletic clade. The trees also display several relationships proposed by past studies, as well as new relevant relationships between and within the main genera of Corynebacteriales: Corynebacterium, Mycobacterium, Nocardia, Rhodococcus, and Gordonia. An implementation of the method in Python is available on GitHub at https://github.com/UdeS-CoBIUS/EXECT (last accessed April 2, 2020).

Complete Genome Sequence of Alteromonas sp. Strain I4, Isolated from the Japan Sea

A novel strain of Alteromonas, I4, was isolated from a shallow beach of the Japan Sea. Here, we report the complete genome sequence of I4; this strain contains a single circular chromosome (5,133,645 bp; G+C content, 48.4%) and a single circular putative plasmid (123,836 bp; G+C content, 45.1%).

Occurrence of randomly recombined functional 16S rRNA genes in Thermus thermophilus suggests genetic interoperability and promiscuity of bacterial 16S rRNAs

Based on the structural complexity of ribosomes, 16S rRNA genes are considered species-specific and hence used for bacterial phylogenetic analysis. However, a growing number of reports suggest the occurrence of horizontal gene transfer, raising genealogical questions. Here we show the genetic interoperability and promiscuity of 16S rRNA in the ribosomes of an extremely thermophilic bacterium, Thermus thermophilus. The gene in this thermophile was systematically replaced with a diverse array of heterologous genes, resulting in the discovery of various genes that supported growth, some of which were from different phyla. Moreover, numerous functional chimeras were spontaneously generated. Remarkably, cold-adapted mutants were obtained carrying chimeric or full-length heterologous genes, indicating that horizontal gene transfer promoted adaptive evolution. The ribosome may well be understood as a patchworked supramolecule comprising patchworked components. We here propose the “random patch model” for ribosomal evolution.

Functional metagenomic approach to identify overlooked antibiotic resistance mutations in bacterial rRNA

Our knowledge as to how bacteria acquire antibiotic resistance is still fragmented, especially for the ribosome-targeting drugs. In this study, with the aim of finding novel mechanisms that render bacteria resistant to the ribosome-targeting antibiotics, we developed a general method to systematically screen for antibiotic resistant 16 S ribosomal RNAs (rRNAs), which are the major target for multiple antibiotics (e.g. spectinomycin, tetracycline, and aminoglycosides), and identify point mutations therein. We used Escherichia coli ∆7, a null mutant of the rrn (ribosomal RNA) operons, as a surrogate host organism to construct a metagenomic library of 16 S rRNA genes from the natural (non-clinical) environment. The library was screened for spectinomycin resistance to obtain four resistant 16 S rRNA genes from non-E. coli bacterial species. Bioinformatic analysis and site-directed mutagenesis identified three novel mutations - U1183C (the first mutation discovered in a region other than helix 34), and C1063U and U1189C in helix 34 - as well as three well-described mutations (C1066U, C1192G, and G1193A). These results strongly suggest that uncharacterized antibiotic resistance mutations still exist, even for traditional antibiotics.

Phylogenetic Network Analysis Revealed the Occurrence of Horizontal Gene Transfer of 16S rRNA in the Genus Enterobacter

Horizontal gene transfer (HGT) is a ubiquitous genetic event in bacterial evolution, but it seldom occurs for genes involved in highly complex supramolecules (or biosystems), which consist of many gene products. The ribosome is one such supramolecule, but several bacteria harbor dissimilar and/or chimeric 16S rRNAs in their genomes, suggesting the occurrence of HGT of this gene. However, we know little about whether the genes actually experience HGT and, if so, the frequency of such a transfer. This is primarily because the methods currently employed for phylogenetic analysis (e.g., neighbor-joining, maximum likelihood, and maximum parsimony) of 16S rRNA genes assume point mutation-driven tree-shape evolution as an evolutionary model, which is intrinsically inappropriate to decipher the evolutionary history for genes driven by recombination. To address this issue, we applied a phylogenetic network analysis, which has been used previously for detection of genetic recombination in homologous alleles, to the 16S rRNA gene. We focused on the genus Enterobacter, whose phylogenetic relationships inferred by multi-locus sequence alignment analysis and 16S rRNA sequences are incompatible. All 10 complete genomic sequences were retrieved from the NCBI database, in which 71 16S rRNA genes were included. Neighbor-joining analysis demonstrated that the genes residing in the same genomes clustered, indicating the occurrence of intragenomic recombination. However, as suggested by the low bootstrap values, evolutionary relationships between the clusters were uncertain. We then applied phylogenetic network analysis to representative sequences from each cluster. We found three ancestral 16S rRNA groups; the others were likely created through recursive recombination between the ancestors and chimeric descendants. Despite the large sequence changes caused by the recombination events, the RNA secondary structures were conserved. Successive intergenomic and intragenomic recombination thus shaped the evolution of 16S rRNA genes in the genus Enterobacter.

Comparative RNA function analysis reveals high functional similarity between distantly related bacterial 16 S rRNAs

The 16 S rRNA sequence has long been used uncritically as a molecular clock to infer phylogenetic relationships among prokaryotes without fully elucidating the evolutionary changes that this molecule undergoes. In this study, we investigated the functional evolvability of 16 S rRNA, using comparative RNA function analyses between the 16 S rRNAs of Escherichia coli (Proteobacteria) and Acidobacteria (78% identity, 334 nucleotide differences) in the common genetic background of E. coli. While the growth phenotype of an E. coli mutant harboring the acidobacterial gene was disrupted significantly, it was restored almost completely following introduction of a 16 S rRNA sequence with a single base-pair variation in helix 44; the remaining 332 nucleotides were thus functionally similar to those of E. coli. Our results suggest that 16 S rRNAs share an inflexible cradle structure formed by ribosomal proteins and have evolved by accumulating species-specific yet functionally similar mutations. While this experimental evidence suggests the neutral evolvability of 16 S rRNA genes and hence satisfies the necessary requirements to use the sequence as a molecular clock, it also implies the promiscuous nature of the 16 S rRNA gene, i.e., the occurrence of horizontal gene transfer among bacteria.