Figure 5 : The yeaG-dependent adaptive response to sustained N starvation involves the transcriptional repression of mqsR/mqsA and dinJ/yafQ toxin-antitoxin genes.

From: Adaptation to sustained nitrogen starvation by Escherichia coli requires the eukaryote-like serine/threonine kinase YeaG

Figure 5

(A) Expression levels of ten E. coli TA gene pairs in wild-type and ∆yeaG mutant strain calculated as fold change in mRNA between N+ and N-24 h N-starved conditions and normalised to 16S expression. Error bars represent sd (n = 2; except mqsR/mqsA, where n = 4). (B–D) Expression levels of cspD, rpoS and cspE in wild-type and ∆yeaG mutant strain calculated as fold change in mRNA between N+ and N-24 h N starved conditions and normalised to 16S expression. Error bars represent sd (n = 4). (E) Levels of RpoS are reduced in ∆yeaG mutant strain following 24 h N starvation. Representative immunoblot of whole-cell extracts of bacterial cells sampled after 20 min and 24 h of N starvation probed with anti-RpoS and anti-DnaK (loading control) antibody. Graph shows quantification of bands by densitometry (n = 3), calculated as the ratio in Optical Density between the bands corresponding to RpoS and DnaK. Error bars represent sd (n = 4). (F) RpoS-dependent catalase activity is impaired in the ∆yeaG mutant strain following 24 h of N starvation. Catalase activity was assessed as a function of concentration of H2O2 remaining in solution after incubation with 24 h N-starved wild-type, ∆yeaG or ∆katE bacterial lysates. Error bars represent sd (n = 3). (G) Deletion of dinJ/yafQ and mqsR/mqsA TA modules in the ∆yeaG strain leads to complementation of the mutant phenotype, whilst deletion of only one TA modules in the ∆yeaG strain leads to only partial complementation. The ‘recovery’ growth curves for wild-type, ∆yeaG, ∆dinJyafQyeaG, ∆mqsR∆mqsA∆yeaG and ∆dinJyafQ∆mqsR∆mqsA∆yeaG mutant strains were obtained by OD600nm readings at hourly time points. (H.) Expression levels of sdhB, rpsV, katE, pdhR, bolA and poxB at N-24 calculated as fold change in mRNA between the wild-type and ∆yeaG mutant strain and normalised to 16S expression. Error bars represent sd (n = 3). Statistical analyses for all data-sets were performed by Student’s t test (*P < 0.05; **P < 0.01) relative to the wild-type strain.