One of the best-studied transcriptional regulatory proteins in bacteria is the Escherichia coli catabolite repressor protein (CRP) that when complexed with 3’-5’-cyclic AMP (cAMP) changes its conformation and interacts with specific DNA-sequences. CRP DNA-binding can result in positive or negative regulation of gene expression depending on the position of its interaction with respect to RNA polymerase binding site. The aim of this work is to review the biological role and phylogenetic relations that some members of the CRP family of transcriptional regulators (also known as cAMP receptor protein family) have in different bacterial species. This work is not intended to give an exhaustive revision of bacterial CRP-orthologs, but to provide examples of the role that these proteins play in the expression of genes that are fundamental for the life style of some bacterial species. We highlight the conservation of their structural characteristics and of their binding to conserved-DNA sequences, in contrast to their very diverse repertoire of gene activation. CRP activates a wide variety of fundamental genes for the biological characteristic of each bacterial species, which in several instances form part of their core-genome (defined as the gene sequences present in all members of a bacterial species). We present evidence that support the fact that some of the transcriptional regulators that belong to the CRP family in different bacterial species, and some of the genes that are regulated by them, can be inherited by horizontal gene transfer. These data are discussed in the framework of bacterial evolution models.

Pseudomonas aeruginosa is an opportunistic pathogen that presents a complex regulatory network called ‘quorum-sensing’, which is responsible for the transcription of genes coding for several traits implicated in its pathogenicity. Strain 148 is a dolphin isolate that has been shown to produce quorum-sensing-regulated virulence traits and to be virulent in a mouse model, despite the fact that it contains a 20-kbp deletion that eliminates from the chromosome the lasR gene and the lasI promoter. LasR is a key quorum-sensing transcriptional regulator that, when coupled with the autoinducer 3-oxo-dodecanoyl homoserine lactone (3O-C12-HSL) produced by LasI, activates transcription of genes coding for some virulence-associated traits such as elastase, lasI, rhlI and rhlR. RhlR is also a key quorum-sensing transcriptional regulator that, when interacting with the autoinducer butanoyl homoserine lactone (C4-HSL) that is produced by the synthase RhlI, activates the genes involved in the synthesis of some virulence-associated traits, as rhamnolipids and pyocyanin. We describe that in P. aeruginosa 148, the LasR/3O-C12-HSL-independent rhlR transcriptional activation is due to the release of the negative effect of Vfr (a CRP-ortholog) caused by the insertion of an IS element in vfr, and that rhlI transcription is driven from the rhlR promoter, forming the rhlR-I operon.

Pseudomonas aeruginosa (P. aeruginosa) is a bacterium of medical concern, known for its potential to persist in diverse environments due to its metabolic capacity. Its survival ability is linked to its relatively large genome of 5.5-7 Mbp, from which several genes are employed in overcoming conventional antibiotic treatments and promoting resistance. The worldwide prevalence of antibiotic-resistant clones of P. aeruginosa necessitates novel approaches to researching their multiple resistance mechanisms, such as the use of antimicrobial peptides (AMPs). In this review, we briefly discuss the epidemiology of the resistant strains of P. aeruginosa and then describe their resistance mechanisms. Next, we explain the biology of AMPs, enlist the present database platforms that describe AMPs, and discuss their usefulness and limitations in treating P. aeruginosa strains. Finally, we present 13 AMPs with theoretical action against P. aeruginosa, all of which we evaluated in silico in this work. Our results suggest that the AMPs we evaluated have a carpet-like mode of action with a membranolytic function in Gram-positive and Gram-negative bacteria, with clear potential of synthesis for in vitro evaluation.