Spot 42 was discovered in Escherichia coli nearly 40 years ago as an abundant, small and unstable RNA. Its biological role remained obscure until it was shown to cause discoordinate expression of the galactose operon (gal operon). Recently Spot 42 has also been implicated in having broader roles in the central and secondary metabolism. Spot 42 is encoded by the spf gene. The gene is ubiquitous in the Vibrionaceae family of gamma-proteobacteria, which includes a number of serious pathogens of humans and animals, including the infamous Vibrio cholerae. One member of this family, Aliivibrio salmonicida, causes cold-water vibriosis in farmed Atlantic salmon. Its genome encodes Spot 42 with 84 % identity to E. coli Spot 42 (spf). We generated a A. salmonicida spf deletion mutant. We then and used microarray and Northern blot analyses to monitor global effects on the transcriptome in order to provide insights into the biological roles of Spot 42 in this bacterium. In the presence of glucose we found a surprisingly large number of ≥2× differentially expressed genes, and several major cellular processes were affected, such as carbohydrate metabolism and transport, motility and chemotaxis, iron homeostasis and quorum sensing. A gene encoding a pirin-like protein (VSAL_I1200) showed an on/off expression pattern in the presence/absence of Spot 42, which suggests that Spot 42 plays a key regulatory role in the central metabolism by regulating the switch between fermentation and respiration. Interestingly, in a global search we discovered a sRNA, named VSsrna24, which is encoded immediately downstream of spf. This new sRNA has an expression pattern opposite to that of Spot 42, and its expression is highly dependent on glucose. Our hypothesis is that this novel sRNA works in concert with Spot 42 to regulate carbohydrate metabolism and uptake.
Overall design: Two-condition experiment, wild type cells (control samples) vs. spf mutants grown in A. salmonicida-specific minimal media (ASMM) (stimulated samples). Samples were prepared by culturing the A. salmonicida wild type and a spf deletion mutant strains at 12 °C in ASMM without any added carbon source to OD 600nm 0.4. At this density glucose to 44.4 mM was added. Samples were collected 15 min after stimulation. Biological replicates for each sample: 3 wild type, 3 spf mutant, independently grown and harvested. One replicate per array.
Less...