Genome erosion and evidence for an intracellular niche - exploring the biology of mycoplasmas in Atlantic salmon

Mycoplasmas are the smallest autonomously self-replicating life form on the planet. Members of this bacterial genus are known to parasitise a wide array of metazoans including vertebrates. Whilst much research has been significant targeted at parasitic mammalian mycoplasmas, very little is known about their role in other vertebrates. In the current study, we aim to explore the biology of mycoplasmas in Atlantic Salmon, a species of major significance for aquaculture, including cellular niche, genome size structure and gene content. Using fluorescent in-situ hybridisation (FISH), mycoplasmas were targeted in epithelial tissues across the digestive tract (stomach, pyloric caecum and midgut) from different development stages (eggs, parr, subadult) of farmed Atlantic salmon (Salmo salar), and we present evidence for an intracellular niche for some of the microbes visualised. Via shotgun metagenomic sequencing, a nearly complete, albeit small, genome (~0.57 MB) as assembled from a farmed Atlantic salmon subadult. Phylogenetic analysis of the recovered genome revealed taxonomic proximity to other salmon derived mycoplasmas, as well as to the human pathogen Mycoplasma penetrans (~1.36 Mb). We annotated coding sequences and identified riboflavin pathway encoding genes and sugar transporters, the former potentially consistent with micronutrient provisioning in salmonid development. Our study provides insights into mucosal adherence, the cellular niche and gene catalog of Mycoplasma in the gut ecosystem of the Atlantic salmon, suggesting a high dependency of this minimalist bacterium on its host. Further study is required to explore and functional role of Mycoplasma in the nutrition and development of its salmonid host.

Comparison of DNA migrations in two clamped homogeneous electric field chambers of different sizes. Relation between sample thickness and electrophoresis time

We present here a method to compare the mathematical descriptions of DNA migration per pulse as a function of pulse time. It is based on obtaining robust estimates and variances of DNA reorientation time, migration velocities during and after DNA reorientation; and on the statistical comparisons of these estimates. We demonstrated an equal description for the migration per pulse of each DNA molecule separated under identical conditions in clamped homogeneous electric field (CHEF) and miniCHEF chambers. However, miniCHEF resolved the patterns in shorter times, because it uses thinner samples. The relationship between sample thickness and CHEF run time is also presented.

Secretion and glycosylation of Clostridium thermocellum endoglucanase A encoded by the celA gene in Saccharomyces cerevisiae

The Clostridium thermocellum celA gene encoding endoglucanase A is expressed in Saccharomyces cerevisiae but the enzyme produced from the native celA gene is not secreted. After removal of the bacterial signal peptide-coding sequence, the gene was fused to the promoter and prepro segment of the S. cerevisiae MF alpha 1 gene. This construction directs secretion of active endoglucanase A into the culture medium when introduced in yeast on either replicating or integrating vectors. Secretion of endoglucanase A required growth of transformants on rich medium. The secreted enzyme is a 97,000 Da glycoprotein containing about half of its molecular weight as carbohydrate. This new gene fusion could facilitate further research on protein secretion in yeast by using a cellulase as a marker enzyme.