The actinomyceteCorynebacterium glutamicumgrows as rod-shaped cells by zonal peptidoglycan synthesis at the cell poles. In this bacterium, experimental depletion of the polar DivIVA protein (DivIVA_Cg) resulted in the inhibition of polar growth; consequently, these cells exhibited a coccoid morphology. This result demonstrated that DivIVA is required for cell elongation and the acquisition of a rod shape. DivIVA fromStreptomycesorMycobacteriumlocalized to the cell poles of DivIVA_Cg-depletedC. glutamicumand restored polar peptidoglycan synthesis, in contrast to DivIVA proteins fromBacillus subtilisorStreptococcus pneumoniae, which localized at the septum ofC. glutamicum. This confirmed that DivIVAs from actinomycetes are involved in polarized cell growth. DivIVA_Cglocalized at the septum after cell wall synthesis had started and the nucleoids had already segregated, suggesting that inC. glutamicumDivIVA is not involved in cell division or chromosome segregation.

Time-lapse imaging ofStreptomyceshyphae revealed foci of the essential protein DivIVA at sites where lateral branches will emerge. Overexpression experiments showed that DivIVA foci can trigger establishment of new zones of cell wall assembly, suggesting a key role of DivIVA in directing peptidoglycan synthesis and cell shape inStreptomyces.

Corynebacterium glutamicum is able to grow in media containing up to 12 mM arsenite and 500 mM arsenate and is one of the most arsenic-resistant microorganisms described to date. Two operons ( ars1 and ars2 ) involved in arsenate and arsenite resistance have been identified in the complete genome sequence of Corynebacterium glutamicum . The operons ars1 and ars2 are located some distance from each other in the bacterial chromosome, but they are both composed of genes encoding a regulatory protein ( arsR ), an arsenite permease ( arsB ), and an arsenate reductase ( arsC ); operon ars1 contains an additional arsenate reductase gene ( arsC1′ ) located immediately downstream from arsC1 . Additional arsenite permease and arsenate reductase genes ( arsB3 and arsC4 ) scattered on the chromosome were also identified. The involvement of ars operons in arsenic resistance in C. glutamicum was confirmed by gene disruption experiments of the three arsenite permease genes present in its genome. Wild-type and arsB3 insertional mutant C. glutamicum strains were able to grow with up to 12 mM arsenite, whereas arsB1 and arsB2 C. glutamicum insertional mutants were resistant to 4 mM and 9 mM arsenite, respectively. The double arsB1-arsB2 insertional mutant was resistant to only 0.4 mM arsenite and 10 mM arsenate. Gene amplification assays of operons ars1 and ars2 in C. glutamicum revealed that the recombinant strains containing the ars1 operon were resistant to up to 60 mM arsenite, this being one of the highest levels of bacterial resistance to arsenite so far described, whereas recombinant strains containing operon ars2 were resistant to only 20 mM arsenite. Northern blot and reverse transcription-PCR analysis confirmed the presence of transcripts for all the ars genes, the expression of arsB3 and arsC4 being constitutive, and the expression of arsR1 , arsB1 , arsC1 , arsC1′ , arsR2 , arsB2 , and arsC2 being inducible by arsenite.

Antimicrobial resistance is becoming one of the most important human health issues. Accordingly, the research focused on finding new antibiotherapeutic strategies is again becoming a priority for governments and major funding bodies. The development of treatments based on the generation of oxidative stress with the aim to disrupt the redox defenses of bacterial pathogens is an important strategy that has gained interest in recent years. This approach is allowing the identification of antimicrobials with repurposing potential that could be part of combinatorial chemotherapies designed to treat infections caused by recalcitrant bacterial pathogens. In addition, there have been important advances in the identification of novel plant and bacterial secondary metabolites that may generate oxidative stress as part of their antibacterial mechanism of action. Here, we revised the current status of this emerging field, focusing in particular on novel oxidative stress-generating compounds with the potential to treat infections caused by intracellular bacterial pathogens.

The genes involved in gluconate catabolism ( gntP and gntK ) in Corynebacterium glutamicum are scattered in the chromosome, and no regulatory genes are apparently associated with them, in contrast with the organization of the gnt operon in Escherichia coli and Bacillus subtilis . In C. glutamicum , gntP and gntK are essential genes when gluconate is the only carbon and energy source. Both genes contain upstream regulatory regions consisting of a typical promoter and a hypothetical cyclic AMP (cAMP) receptor protein (CRP) binding region but lack the expected consensus operator region for binding of the GntR repressor protein. Expression analysis by Northern blotting showed monocistronic transcripts for both genes. The expression of gntP and gntK is not induced by gluconate, and the gnt genes are subject to catabolite repression by sugars, such as glucose, fructose, and sucrose, as was detected by quantitative reverse transcription-PCR (qRT-PCR). Specific analysis of the DNA promoter sequences (P gntK and P gntP ) was performed using bifunctional promoter probe vectors containing mel (involved in melanin production) or e gfp2 (encoding a green fluorescent protein derivative) as the reporter gene. Using this approach, we obtained results parallel to those from qRT-PCR. An applied example of in vivo gene expression modulation of the divIVA gene in C. glutamicum is shown, corroborating the possible use of the gnt promoters to control gene expression. glxR (which encodes GlxR, the hypothetical CRP protein) was subcloned from the C. glutamicum chromosomal DNA and overexpressed in corynebacteria; we found that the level of gnt expression was slightly decreased compared to that of the control strains. The purified GlxR protein was used in gel shift mobility assays, and a specific interaction of GlxR with sequences present on P gntP and P gntK fragments was detected only in the presence of cAMP.