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LtrR is a LysR-type regulator involved in the positive expression of ompR to promote ompC and ompF expression. This regulatory network is fundamental for the control of bacterial transformation and resistance to the bile salt sodium deoxycholate in Salmonella enterica serovar Typhi. In this work, the transcriptional regulation of ltrR was characterized, revealing that the use of alternative promoters results in two transcripts. The larger one, the ltrR2 mRNA, was repressed at promoter and coding regions by H-NS, whereas Lrp repressed its expression at the coding region. In the case of the second and shorter ltrR1 transcript, it was repressed only at the coding region by H-NS and Lrp. Remarkably, pH 7.5 is a positive signal involved in the transcriptional expression of both ltrR units. Translational fusions and Western blot experiments demonstrated that ltrR2 and ltrR1 mRNAs encode the LtrR2 and LtrR1 proteins. This study adds new data on the complex genetic and regulatory characteristics of one of the most predominant types of transcriptional factors in bacteria, the LysR-type transcriptional regulators. [ABSTRACT FROM AUTHOR]

The ability of Escherichia coli to grow on L-lactate as a sole carbon source depends on the expression of the lldPRD operon. A striking feature of this operon is that the transcriptional regulator (LldR) encoding gene is located between the permease (LldP) and the dehydrogenase (LldD) encoding genes. In this study we report that dosage of the LldP, LldR, and LldD proteins is not modulated on the transcriptional level. Instead, modulation of protein dosage is primarily correlated with RNase E-dependent mRNA processing events that take place within the lldR mRNA, leading to the immediate inactivation of lldR , to differential segmental stabilities of the resulting cleavage products, and to differences in the translation efficiencies of the three cistrons. A model for the processing events controlling the molar quantities of the proteins in the lldPRD operon is presented and discussed. Importance Adjustment of gene expression is critical for proper cell function. For the case of polycistronic transcripts, posttranscriptional regulatory mechanisms can be used to fine-tune the expression of individual cistrons. Here, we elucidate how protein dosage of the Escherichia coli lldPRD operon, which presents the paradox of having the gene encoding a regulator protein located between genes that code for a permease and an enzyme, is regulated. Our results demonstrate that the key event in this regulatory mechanism involves the RNase E-dependent cleavage of the primary lldPRD transcript at internal site(s) located within the lldR cistron, resulting in a drastic decrease of intact lldR mRNA, to differential segmental stabilities of the resulting cleavage products, and to differences in the translation efficiencies of the three cistrons., (Copyright © 2020 American Society for Microbiology.)

LeuO is a LysR-type transcriptional regulator (LTTR) that has been described to be a global regulator in Escherichia coli and Salmonella enterica, since it positively and negatively regulates the expression of genes involved in multiple biological processes. LeuO is comprised of an N-terminal DNA-binding domain (DBD) with a winged helix-turn-helix (wHTH) motif and of a long linker helix (LH) involved in dimerization that connects the DBD with the C-terminal effector-binding domain (EBD) or regulatory domain (RD; which comprises subdomains RD-I and RD-II). Here we show that the oligomeric structure of LeuO is a tetramer that binds with high affinity to DNA. A collection of single amino acid substitutions in the LeuO DBD indicated that this region is involved in oligomerization, in positive and negative regulation, as well as in DNA binding. Mutants with point mutations in the central and C-terminal regions of RD-I were affected in transcriptional activation. Deletion of the RD-II and RD-I C-terminal subdomains affected not only oligomerization but also DNA interaction, showing that they are involved in positive and negative regulation. Together, these data demonstrate that not only the C terminus but also the DBD of LeuO is involved in oligomer formation; therefore, each LeuO domain appears to act synergistically to maintain its regulatory functions in Salmonella enterica serovar Typhi., (Copyright © 2014, American Society for Microbiology. All Rights Reserved.)

The genus Burkholderia includes pathogens of plants and animals and some human opportunistic pathogens, such as the Burkholderia cepacia complex (Bcc), but most species are nonpathogenic, plant associated, and rhizospheric or endophytic. Since rhizobacteria expressing ACC (1-aminocyclopropane-1-carboxylate) deaminase may enhance plant growth by lowering plant ethylene levels, in this work we investigated the presence of ACC deaminase activity and the acdS gene in 45 strains, most of which are plant associated, representing 20 well-known Burkholderia species. The results demonstrated that ACC deaminase activity is a widespread feature in the genus Burkholderia, since 18 species exhibited ACC deaminase activities in the range from 2 to 15 mumol of alpha-ketobutyrate/h/mg protein, which suggests that these species may be able to modulate ethylene levels and enhance plant growth. In these 18 Burkholderia species the acdS gene sequences were highly conserved (76 to 99% identity). Phylogenetic analysis of acdS gene sequences in Burkholderia showed tight clustering of the Bcc species, which were clearly distinct from diazotrophic plant-associated Burkholderia species. In addition, an acdS knockout mutant of the N(2)-fixing bacterium Burkholderia unamae MTl-641(T) and a transcriptional acdSp-gusA fusion constructed in this strain showed that ACC deaminase could play an important role in promotion of the growth of tomato plants. The widespread ACC deaminase activity in Burkholderia species and the common association of these species with plants suggest that this genus could be a major contributor to plant growth under natural conditions.

Salmonella enterica serovar Typhimurium mutants with mutations in the ompS1 and ompS2 genes, which code for quiescent porins, were nevertheless highly attenuated for virulence in a mouse model, indicating a role in pathogenesis. Similarly, a strain with a mutation in the gene coding for LeuO, a positive regulator of ompS2, was also attenuated.

Sinorhizobium sp. strain BR816 possesses two nodPQ copies, providing activated sulfate (3'-phosphoadenosine-5'-phosphosulfate [PAPS]) needed for the biosynthesis of sulfated Nod factors. It was previously shown that the Nod factors synthesized by a nodPQ double mutant are not structurally different from those of the wild-type strain. In this study, we describe the characterization of a third sulfate activation locus. Two open reading frames were fully characterized and displayed the highest similarity with the Sinorhizobium meliloti housekeeping ATP sulfurylase subunits, encoded by the cysDN genes. The growth characteristics as well as the levels of Nod factor sulfation of a cysD mutant (FAJ1600) and a nodP1 nodQ2 cysD triple mutant (FAJ1604) were determined. FAJ1600 shows a prolonged lag phase only with inorganic sulfate as the sole sulfur source, compared to the wild-type parent. On the other hand, FAJ1604 requires cysteine for growth and produces sulfate-free Nod factors. Apigenin-induced nod gene expression for Nod factor synthesis does not influence the growth characteristics of any of the strains studied in the presence of different sulfur sources. In this way, it could be demonstrated that the "household" CysDN sulfate activation complex of Sinorhizobium sp. strain BR816 can additionally ensure Nod factor sulfation, whereas the symbiotic PAPS pool, generated by the nodPQ sulfate activation loci, can be engaged for sulfation of amino acids. Finally, our results show that rhizobial growth defects are likely the reason for a decreased nitrogen fixation capacity of bean plants inoculated with cysD mutant strains, which can be restored by adding methionine to the plant nutrient solution.

Ensifer adhaerens is a soil bacterium that attaches to other bacteria and may cause lysis of these other bacteria. Based on the sequence of its small-subunit rRNA gene, E. adhaerens is related to Sinorhizobium spp. E. adhaerens ATCC 33499 did not nodulate Phaseolus vulgaris (bean) or Leucaena leucocephala, but with symbiotic plasmids from Rhizobium tropici CFN299 it formed nitrogen-fixing nodules on both hosts. The nodule isolates were identified as E. adhaerens isolates by growth on selective media.

We determined the activities of selected enzymes involved in carbon metabolism in free-living cells of Rhizobium tropici CFN299 grown in minimal medium with different carbon sources and in bacteroids of the same strain. The set of enzymatic activities in sucrose-grown cells suggests that the pentose phosphate pathway, with the participation of the Entner-Doudoroff pathway, is probably the primary route for sugar catabolism. In glutamate- and malate-grown cells, high activities of the gluconeogenic enzymes (phosphoenolpyruvate carboxykinase, fructose-6-phosphate aldolase, and fructose bisphosphatase) were detected. In bacteroids, isolated in Percoll gradients, the levels of activity for many of the enzymes measured were similar to those of malate-grown cells, except that higher activities of glucokinase, glucose-6-phosphate dehydrogenase, and NAD-dependent phosphogluconate dehydrogenase were detected. Phosphoglucomutase and UDP glucose pyrophosphorylase showed high and constant levels under all growth conditions and in bacteroids.