[Show abstract][Hide abstract] ABSTRACT: The taxonomic composition of a microbial community can be deduced by analysing its ribosomal RNA (rRNA) gene content by e.g. high-throughput DNA sequencing or DNA-chips. Such methods are typically based on polymerase chain reaction (PCR) amplification of rRNA gene sequences using broad taxonomic-range PCR primers. In these analyses the use of optimal primers is crucial for achieving an unbiased representation of community composition. Here we present the computer program DegePrime, that for each position of a multiple sequence alignment finds a degenerate oligomer of as high coverage as possible, and outputs its coverage among taxonomic divisions. We show that our novel heuristic, which we call weighted randomised combination, performs better than previously described algorithms for solving the maximum coverage degenerate primer design problem. We previously used DegePrime to design a broad taxonomic range primer pair that targets the bacterial V3-V4 region (341F-805R) and we here use the program to significantly increase the coverage of a primer pair (515F-806R) widely used for Illumina-based surveys of bacterial and archaeal diversity. By comparison with shotgun metagenomics we show that the primers give an accurate representation of microbial diversity in natural samples.
[Show abstract][Hide abstract] ABSTRACT: Campylobacter jejuni is widespread in the environment and is the major cause of bacterial gastroenteritis in humans. In the present study we use microarray-based comparative genomic hybridizations (CGH), pulsed-field gel electrophoresis (PFGE) and multilocus sequence typing (MLST) to analyze closely related C. jejuni isolates from chicken and human infection.
With the exception of one isolate, the microarray data clusters the isolates according to the five groups determined by PFGE. In contrast, MLST defines only three genotypes among the isolates, indicating a lower resolution. All methods show that there is no inherit difference between isolates infecting humans and chicken, suggesting a common underlying population of C. jejuni. We further identify regions that frequently differ between isolates, including both previously described and novel regions. Finally, we show that genes that belong to certain functional groups differ between isolates more often than expected by chance.
In this study we demonstrated the utility of 70-mer oligonucleotide microarrays for genotyping of Campylobacter jejuni isolates, with resolution outperforming MLST.
[Show abstract][Hide abstract] ABSTRACT: Helicobacter pylori infection is exceptionally prevalent and is considered to be acquired primarily early in life through person-to-person transmission within the family. H. pylori is a genetically diverse bacterial species, which may facilitate adaptation to new hosts and persistence for decades. The present study aimed to explore the genetic diversity of clonal isolates from a mother and her three children in order to shed light on H. pylori transmission and host adaptation.
Two different H. pylori strains and strain variants were identified in the family members by PCR-based molecular typing and sequencing of five loci. Genome diversity was further assessed for 15 isolates by comparative microarray hybridizations. The microarray consisted of 1,745 oligonucleotides representing the genes of two previously sequenced H. pylori strains. The microarray analysis detected a limited mean number (+/- standard error) of divergent genes between clonal isolates from the same and different individuals (1 +/- 0.4, 0.1%, and 3 +/- 0.3, 0.2%, respectively). There was considerable variability between the two different strains in the family members (147 +/- 4, 8%) and for all isolates relative to the two sequenced reference strains (314 +/- 16, 18%). The diversity between different strains was associated with gene functional classes related to DNA metabolism and the cell envelope.
The present data from clonal H. pylori isolates of family members do not support that transmission and host adaptation are associated with substantial sequence diversity in the bacterial genome. However, important phenotypic modifications may be determined by additional genetic mechanisms, such as phase-variation. Our findings can aid further exploration of H. pylori genetic diversity and adaptation.