Bacterial conversion of folinic acid is required for antifolate resistance

A new mathematical model of folate homeostasis in E. coli highlights the potential importance of the folinic acid futile cycle in cell growth

Folate (vitamin B9) plays a central role in one-carbon metabolism in prokaryotes and eukaryotes. This pathway mediates the transfer of one-carbon units, playing a crucial role in nucleotide synthesis, methylation, and amino acid homeostasis. The folinic acid futile cycle adds a layer of intrigue to this pathway, due to its associations with metabolism, cell growth, and dormancy. It also introduces additional complexity to folate metabolism. A logical way to deal with such complexity is to examine it by using mathematical modelling. This work describes the construction and analysis of a model of folate metabolism, which includes the folinic acid futile cycle. This model was tested under three in silico growth conditions. Model simulations revealed: 1) the folate cycle behaved as a stable biochemical system in three growth states (slow, standard, and rapid); 2) the initial concentration of serine had the greatest impact on metabolite concentrations; 3) 5-formyltetrahydrofolate cyclo-ligase (5-FCL) activity had a significant impact on the levels of the 7 products that carry the one-carbon donated from folates, and the redox couple NADP/NADPH; this was particularly evident in the rapid growth state; 4) 5-FCL may be vital to the survival of the cells by maintaining low levels of homocysteine, as high levels can induce toxicity; and 5) the antifolate therapeutic trimethoprim had a greater impact on folate metabolism with higher nutrient availability. These results highlight the important role of 5-FCL in intracellular folate homeostasis and mass generation under different metabolic scenarios.

Tissue residue distribution and withdrawal time estimation of trimethoprim and sulfachloropyridazine in Yugan black-bone fowl (Gallus gallus domesticus Brisson)

Black-bone fowl are different from ordinary broilers in appearance and are considered to have rich nutritional properties. However, the metabolism of therapeutic drugs in black-bone fowl remains unclear. This study aimed to determine the tissue residue depletion kinetics of trimethoprim and sulfachloropyridazine in Yugan black-bone fowl, after daily oral administrations for 5 days at 4 mg/kg bw/day trimethoprim and 20 mg/kg bw/day sulfachloropyridazine, and to calculate the withdrawal times. After consecutive oral administrations, the tissues (liver, kidney, muscle and skin/fat) were collected at each of the following time points (0.16, 1, 3, 5, 7, 9, 20, 30 and 40 days). A newly-devised LC-MS/MS method was used to analyse the concentrations of trimethoprim and sulfachlorpyridazine in target tissues. The results showed that sulfachloropyridazine was rapidly metabolised in broilers, and there was no residue in all tissues 3 days post-administration. The concentration of trimethoprim in black-bone fowl skin/fat is the highest, and its metabolism rate is low. After 40 days, the concentration of trimethoprim in skin/fat is still as high as 140.1 ± 58.0 μg/kg, exceeding the maximum residue limit. In order to protect consumers' health, it is suggested that the withdrawal time of TMP in Yugan black-bone fowl is 69 days.

Predicting cancer prognosis and drug response from the tumor microbiome

Tumor gene expression is predictive of patient prognosis in some cancers. However, RNA-seq and whole genome sequencing data contain not only reads from host tumor and normal tissue, but also reads from the tumor microbiome, which can be used to infer the microbial abundances in each tumor. Here, we show that tumor microbial abundances, alone or in combination with tumor gene expression, can predict cancer prognosis and drug response to some extent-microbial abundances are significantly less predictive of prognosis than gene expression, although similarly as predictive of drug response, but in mostly different cancer-drug combinations. Thus, it appears possible to leverage existing sequencing technology, or develop new protocols, to obtain more non-redundant information about prognosis and drug response from RNA-seq and whole genome sequencing experiments than could be obtained from tumor gene expression or genomic data alone.

Transcriptomics and proteomics revealed the psychrotolerant and antibiotic-resistant mechanisms of strain Pseudomonas psychrophila RNC-1 capable of assimilatory nitrate reduction and aerobic denitrification

Aerobic denitrification has been proved to be profoundly affected by temperature and antibiotics, but little is known about how aerobic denitrifiers respond to temperature and antibiotic stress. In this study, the nitrate reduction performance and the intracellular metabolism by a psychrotolerant aerobic denitrifying bacteria, named Pseudomonas psychrophila RNC-1, were systematically investigated at different temperatures (10 °C, 20 °C, 30 °C) and different sulfamethoxazole (SMX) concentrations (0 mg/L, 0.1 mg/L, 0.5 mg/L, 1.0 mg/L, and 5.0 mg/L). The results showed that strain RNC-1 performed satisfactory nitrate removal at 10 °C and 20 °C, but its growth was significantly inhibited at 30 °C. Nitrate removal by strain RNC-1 was slightly promoted in the presence of 0.5 mg/L SMX, whereas it was significantly suppressed with 5.0 mg/L SMX. Nitrogen balance analysis indicated that assimilatory nitrate reduction and dissimilatory aerobic denitrification jointly dominated in the nitrate removal process of strain RNC-1, in which the inhibition effected on assimilation process was much higher than that on the aerobic denitrification process under SMX exposure. Further transcriptomics and proteomics analysis revealed that the psychrotolerant mechanism of strain RNC-1 could be attributed to the up-regulation of RNA translation, energy metabolism, ABC transporters and the over-expression of cold shock proteins, while the down-regulation of oxidative phosphorylation pathway was the primary reason for the deteriorative cell growth at 30 °C. The promotion of nitrate reduction with 0.5 mg/L SMX was related to the up-regulation of amino acid metabolism pathways, while the down-regulation of folate cycle, glycolysis/gluconeogenesis and bacterial chemotaxis pathways were responsible for the inhibition effect at 5.0 mg/L SMX. This work provides a mechanistic understanding of the metabolic adaption of strain RNC-1 under different stress, which is of significance for its application in nitrogen contaminated wastewater treatment processes.

The Pup-Proteasome System Protects Mycobacteria from Antimicrobial Antifolates

Protein turnover via the Pup-proteasome system (PPS) is essential for nitric oxide resistance and virulence of Mycobacterium tuberculosis, the causative agent of tuberculosis. Our study revealed components of PPS as novel determinants of intrinsic antifolate resistance in both M. tuberculosis and nonpathogenic M. smegmatis The lack of expression of the prokaryotic ubiquitin-like protein (Pup) or the ligase, PafA, responsible for ligating Pup to its protein targets, enhanced antifolate susceptibility in M. smegmatis Cross-species expression of M. tuberculosis homologs restored wild-type resistance to M. smegmatis proteasomal mutants. Targeted deletion of prcA and prcB, encoding the structural components of the PPS proteolytic core, similarly resulted in reduced antifolate resistance. Furthermore, sulfonamides were synergistic with acidified nitrite, and the synergy against mycobacteria was enhanced in the absence of proteasomal activity. In M. tuberculosis, targeted mutagenesis followed by genetic complementation of mpa, encoding the regulatory subunit responsible for translocating pupylated proteins to the proteolytic core, demonstrated a similar function of PPS in antifolate resistance. The overexpression of dihydrofolate reductase, responsible for the reduction of dihydrofolate to tetrahydrofolate, or disruption of the Lonely Guy gene, responsible for PPS-controlled production of cytokinins, abolished PPS-mediated antifolate sensitivity. Together, our results show that PPS protects mycobacteria from antimicrobial antifolates via regulating both folate reduction and cytokinin production.

Monomeric NADH-Oxidizing Methylenetetrahydrofolate Reductases from Mycobacterium smegmatis Lack Flavin Coenzyme

5,10-Methylenetetrahydrofolate reductase (MetF/MTHFR) is an essential enzyme in one-carbon metabolism for de novo biosynthesis of methionine. Our in vivo and in vitro analyses of MSMEG_6664/MSMEI_6484, annotated as putative MTHFR in Mycobacterium smegmatis, failed to reveal their function as MTHFRs. However, we identified two hypothetical proteins, MSMEG_6596 and MSMEG_6649, as noncanonical MTHFRs in the bacterium. MTHFRs are known to be oligomeric flavoproteins. Both MSMEG_6596 and MSMEG_6649 are monomeric proteins and lack flavin coenzymes. In vitro, the catalytic efficiency (k _cat/K_m ) of MSMEG_6596 (MTHFR1) for 5,10-CH₂-THF and NADH was ∼13.5- and 15.3-fold higher than that of MSMEG_6649 (MTHFR2). Thus, MSMEG_6596 is the major MTHFR. This interpretation was further supported by better rescue of the E. coli Δmthfr strain by MTHFR1 than by MTHFR2. As identified by liquid chromatography-tandem mass spectrometry, the product of MTHFR1- or MTHFR2-catalyzed reactions was 5-CH₃-THF. The M. smegmatis Δmsmeg_6596 strain was partially auxotrophic for methionine and grew only poorly without methionine or without being complemented with a functional copy of MTHFR1 or MTHFR2. Furthermore, the Δmsmeg_6596 strain was more sensitive to folate pathway inhibitors (sulfachloropyridazine, p-aminosalicylic acid, sulfamethoxazole, and trimethoprim). The studies reveal that MTHFR1 and MTHFR2 are two noncanonical MTHFR proteins that are monomeric and lack flavin coenzyme. Both MTHFR1 and MTHFR2 are involved in de novo methionine biosynthesis and required for antifolate resistance in mycobacteria.IMPORTANCE MTHFR/MetF is an essential enzyme in a one-carbon metabolic pathway for de novo biosynthesis of methionine. MTHFRs are known to be oligomeric flavoproteins. Our in vivo and in vitro analyses of Mycobacterium smegmatis MSMEG_6664/MSMEI_6484, annotated as putative MTHFR, failed to reveal their function as MTHFRs. However, we identified two of the hypothetical proteins, MSMEG_6596 and MSMEG_6649, as MTHFR1 and MTHFR2, respectively. Interestingly, both MTHFRs are monomeric and lack flavin coenzymes. M. smegmatis deleted for the major mthfr (mthfr1) was partially auxotroph for methionine and more sensitive to folate pathway inhibitors (sulfachloropyridazine, para-aminosalicylic acid, sulfamethoxazole, and trimethoprim). The studies reveal that MTHFR1 and MTHFR2 are novel MTHFRs involved in de novo methionine biosynthesis and required for antifolate resistance in mycobacteria.

Functional prediction, characterization, and categorization of operome from Acetoanaerobium sticklandii DSM 519

Acetoanaerobium sticklandii DSM 519 is a hyper-ammonia producing anaerobic bacterium that can be able utilizes amino acids as sole carbon and energy sources for its growth and energetic metabolism. A lack of knowledge on its molecular machinery and 30.5% conserved hypothetical proteins (HPs; operome) hinders the successful utility in biofuel applications. In this study, we have predicted, characterized and categorized its operome whose functions are still not determined accurately using a combined bioinformatics approach. The functions of 64 of the 359 predicted HPs are involved in diverse metabolic subsystems. A. sticklandii operome has consisted of 16% Rossmann fold and 46% miscellaneous folds. Subsystems-based technology has classified 51 HPs contributing to the small-molecular reactions, 26 in macromolecular reactions and 12 in the biosynthesis of cofactors, prosthetic groups and electron carriers. A generality of functions predicted from its operome contributed to the cell cycle, amino acid metabolism, membrane transport, and regulatory processes. Many of them have duplicated functions as paralogs in this genome. A. sticklandii has the ability to compete with invading microorganisms and tolerate abiotic stresses, which can be overwhelmed by the predicted functions of its operome. Results of this study revealed that it has specialized systems for amino acid catabolism-directed solventogenesis and acidogenesis but the level of gene expression may determine the metabolic function in amino acid fermenting niches in the rumina of cattle. As shown by our analysis, the predicted functions of its operome allow us for a better understanding of the growth and physiology at systems-scale.

Investigations of Amino Acids in the 5-Formyltetrahydrofolate Binding Site of 5,10-Methenyltetrahydrofolate Synthetase from Mycoplasma pneumonia

5,10-Methenyltetrahydrofolate synthetase plays a significant role in folate metabolism by catalyzing the conversion of 5-formyltetrahydrofolate into 5,10-methenyltetrahydrofolate. The enzyme is important in some forms of chemotherapy, and it has been implicated in resistance to antifolate antibiotics. A co-crystal structure of the enzyme (1U3G) and primary sequence analysis were used to select highly conserved amino acids in close proximity to bound 5-formyltetrahydrofolate. The amino acids were then investigated using site directed mutagenesis and kinetics. Y123, E55, and F118 were concluded to be important for binding 5-formyltetrahydrofolate in the active site and/or for substrate turnover of the enzyme. Replacement of E55 or Y123 with alanine resulted in no detectable activity. The more subtle replacement of E55 with glutamine was also inactive suggesting an ionic interaction with 5-formyltetrahydrofolate. Mutations to F118 resulted in substantial increases in apparent K_m for both 5-formyltetrahydrofolate and ATP, but did not substantially affect catalytic turnover. Outside the active site, the replacement of Q144 with alanine yielded an enzyme that bound the substrates of ATP and 5-formyltetrahydrofolate with higher apparent K_m values than the wild-type enzyme, but demonstrated a 3.1 fold increase in k_cat.

Mutual potentiation drives synergy between trimethoprim and sulfamethoxazole

Trimethoprim (TMP)-sulfamethoxazole (SMX) is a widely used synergistic antimicrobial combination to treat a variety of bacterial and certain fungal infections. These drugs act by targeting sequential steps in the biosynthetic pathway for tetrahydrofolate (THF), where SMX inhibits production of the THF precursor dihydropteroate, and TMP inhibits conversion of dihydrofolate (DHF) to THF. Consequently, SMX potentiates TMP by limiting de novo DHF production and this mono-potentiation mechanism is the current explanation for their synergistic action. Here, we demonstrate that this model is insufficient to explain the potent synergy of TMP-SMX. Using genetic and biochemical approaches, we characterize a metabolic feedback loop in which THF is critical for production of the folate precursor dihydropterin pyrophosphate (DHPPP). We reveal that TMP potentiates SMX activity through inhibition of DHPPP synthesis. Our study demonstrates that the TMP-SMX synergy is driven by mutual potentiation of the action of each drug on the other.

Targeting intracellular p-aminobenzoic acid production potentiates the anti-tubercular action of antifolates

The ability to revitalize and re-purpose existing drugs offers a powerful approach for novel treatment options against Mycobacterium tuberculosis and other infectious agents. Antifolates are an underutilized drug class in tuberculosis (TB) therapy, capable of disrupting the biosynthesis of tetrahydrofolate, an essential cellular cofactor. Based on the observation that exogenously supplied p-aminobenzoic acid (PABA) can antagonize the action of antifolates that interact with dihydropteroate synthase (DHPS), such as sulfonamides and p-aminosalicylic acid (PAS), we hypothesized that bacterial PABA biosynthesis contributes to intrinsic antifolate resistance. Herein, we demonstrate that disruption of PABA biosynthesis potentiates the anti-tubercular action of DHPS inhibitors and PAS by up to 1000 fold. Disruption of PABA biosynthesis is also demonstrated to lead to loss of viability over time. Further, we demonstrate that this strategy restores the wild type level of PAS susceptibility in a previously characterized PAS resistant strain of M. tuberculosis. Finally, we demonstrate selective inhibition of PABA biosynthesis in M. tuberculosis using the small molecule MAC173979. This study reveals that the M. tuberculosis PABA biosynthetic pathway is responsible for intrinsic resistance to various antifolates and this pathway is a chemically vulnerable target whose disruption could potentiate the tuberculocidal activity of an underutilized class of antimicrobial agents.

Methylfolate Trap Promotes Bacterial Thymineless Death by Sulfa Drugs

The methylfolate trap, a metabolic blockage associated with anemia, neural tube defects, Alzheimer’s dementia, cardiovascular diseases, and cancer, was discovered in the 1960s, linking the metabolism of folate, vitamin B₁₂, methionine and homocysteine. However, the existence or physiological significance of this phenomenon has been unknown in bacteria, which synthesize folate de novo. Here we identify the methylfolate trap as a novel determinant of the bacterial intrinsic death by sulfonamides, antibiotics that block de novo folate synthesis. Genetic mutagenesis, chemical complementation, and metabolomic profiling revealed trap-mediated metabolic imbalances, which induced thymineless death, a phenomenon in which rapidly growing cells succumb to thymine starvation. Restriction of B₁₂ bioavailability, required for preventing trap formation, using an “antivitamin B₁₂” molecule, sensitized intracellular bacteria to sulfonamides. Since boosting the bactericidal activity of sulfonamides through methylfolate trap induction can be achieved in Gram-negative bacteria and mycobacteria, it represents a novel strategy to render these pathogens more susceptible to existing sulfonamides.

Sulfonamides were the first agents to successfully treat bacterial infections, but their use later declined due to the emergence of resistant organisms. Restoration of these drugs may be achieved through inactivation of molecular mechanisms responsible for resistance. A chemo-genomic screen first identified 50 chromosomal loci representing the whole-genome antifolate resistance determinants in Mycobacterium smegmatis. Interestingly, many determinants resembled components of the methylfolate trap, a metabolic blockage exclusively described in mammalian cells. Targeted mutagenesis, genetic and chemical complementation, followed by chemical analyses established the methylfolate trap as a novel mechanism of sulfonamide sensitivity, ubiquitously present in mycobacteria and Gram-negative bacterial pathogens. Furthermore, metabolomic analyses revealed trap-mediated interruptions in folate and related metabolic pathways. These metabolic imbalances induced thymineless death, which was reversible with exogenous thymine supplementation. Chemical restriction of vitamin B₁₂, an important molecule required for prevention of the methylfolate trap, sensitized intracellular bacteria to sulfonamides. Thus, pharmaceutical promotion of the methylfolate trap represents a novel folate antagonistic strategy to render pathogenic bacteria more susceptible to available, clinically approved sulfonamides.

A mathematical model of microbial folate biosynthesis and utilisation: implications for antifolate development

The metabolic biochemistry of folate biosynthesis and utilisation has evolved into a complex network of reactions. Although this complexity represents challenges to the field of folate research it has also provided a renewed source for antimetabolite targets. A range of improved folate chemotherapy continues to be developed and applied particularly to cancer and chronic inflammatory diseases. However, new or better antifolates against infectious diseases remain much more elusive. In this paper we describe the assembly of a generic deterministic mathematical model of microbial folate metabolism. Our aim is to explore how a mathematical model could be used to explore the dynamics of this inherently complex set of biochemical reactions. Using the model it was found that: (1) a particular small set of folate intermediates are overrepresented, (2) inhibitory profiles can be quantified by the level of key folate products, (3) using the model to scan for the most effective combinatorial inhibitions of folate enzymes we identified specific targets which could complement current antifolates, and (4) the model substantiates the case for a substrate cycle in the folinic acid biosynthesis reaction. Our model is coded in the systems biology markup language and has been deposited in the BioModels Database (MODEL1511020000), this makes it accessible to the community as a whole.

High red blood cell folate is associated with an increased risk of death among adults with diabetes, a 15-year follow-up of a national cohort

BACKGROUND AND AIM

To describe the mortality and fatality of diabetes and assess their relationship with the level of red blood cell (RBC) folate.

METHODS AND RESULT

We analyzed the data of 526 adults with diabetes who participated in the National Health and Nutrition Examination Survey (1991-1994) as the baseline examination, and were followed up through December 31, 2006. Estimates of the hazard ratios (HRs) of selected death causes for individuals with different levels of RBC folate were obtained from Cox proportional hazards regression. A total of 295 deaths were recorded by the end of a 15-year follow-up with a mortality rate of 58.48 per 1000 person year (py). Diabetes was listed as a contributing cause for 136 deaths, accounting for 46.1% of the total deaths with a fatality rate 26.96 per 1000 py. Mortality rate for all-cause in the group with upper quartile of RBC folate was almost twice as high as that among the group with lower quartile, 82.75 vs. 44.10 per 1000 py. After adjusting for covariates, including serum concentration of vitamin B12, cotinine, homocysteine and the history of cardio-cerebral vascular diseases assessed at the baseline, the HRs for dying from any causes were 1.00 (reference), 1.82 (95% CI = 1.25-2.66) and 2.10 (1.37-3.20) among diabetic adults with lower, intermediate, and upper quartiles of RBC folate.

CONCLUSION

Diabetes was listed as a contributing cause for less than half of the deaths among adults with diabetes after 15+ years of follow-up; high RBC folate concentration was associated with an elevated risk of death among adults with diabetes.

Mycobacterium tuberculosis folate metabolism and the mechanistic basis for para-aminosalicylic acid susceptibility and resistance

para-Aminosalicylic acid (PAS) entered clinical use in 1946 as the second exclusive drug for the treatment of tuberculosis (TB). While PAS was initially a first-line TB drug, the introduction of more potent antitubercular agents relegated PAS to the second-line tier of agents used for the treatment of drug-resistant Mycobacterium tuberculosis infections. Despite the long history of PAS usage, an understanding of the molecular and biochemical mechanisms governing the susceptibility and resistance of M. tuberculosis to this drug has lagged behind that of most other TB drugs. Herein, we discuss previous studies that demonstrate PAS-mediated disruption of iron acquisition, as well as recent genetic, biochemical, and metabolomic studies that have revealed that PAS is a prodrug that ultimately corrupts one-carbon metabolism through inhibition of the formation of reduced folate species. We also discuss findings from laboratory and clinical isolates that link alterations in folate metabolism to PAS resistance. These advancements in our understanding of the basis of the susceptibility and resistance of M. tuberculosis to PAS will enable the development of novel strategies to revitalize this and other antimicrobial agents for use in the global effort to eradicate TB.

Investigations of amino acids in the ATP binding site of 5,10-methenyltetrahydrofolate synthetase

5-Formyltetrahydrofolate is a compound that is administered as a rescue agent in methotrexate chemotherapy and in 5-fluorouracil chemotherapy for synergistic effects. It has also recently been suggested to play a role in bacterial resistance to antifolate therapy. 5,10-methenyltetrahydrofolate synthetase (MTHFS) is the only enzyme known to catalyze the conversion of this compound to 5,10-methenyltetrahydrofolate along with the hydrolysis of ATP to ADP. To better understand the roles of specific amino acids in the ATP binding pocket of this enzyme, we used site-directed mutagenesis to create 10 modified forms of the Mycoplasma pneumoniae ortholog. The Michaelis constant (K(m)) for each substrate and the turnover number (k(cat)) was determined for each mutant to help elucidate the role of individual amino acids. Data were compared to crystal structures of human and M. pneumoniae orthologs of MTHFS. Results were largely consistent with a simple coulombic and proximity model; the larger the predicted charges of an interaction and the closer those interactions were to the phosphate transferred between the substrates, the greater the reduction in ATP binding and catalytic activity of the enzyme.

Strategies for potentiation of ethionamide and folate antagonists against Mycobacterium tuberculosis

Antifolates inhibit de novo folate biosynthesis, whereas ethionamide targets the mycolate synthetic pathway in Mycobacterium tuberculosis. These antibiotics are effective against M. tuberculosis but their use has been hampered by concerns over toxicity and low therapeutic indexes. With the increasing spread of drug-resistant forms, interest in using old drugs for tuberculosis treatment has been renewed. Specific inhibitors targeting resistance mechanisms could sensitize M. tuberculosis to these available, clinically approved drugs. This review discusses recently developed strategies to boost the antituberculous activity of ethionamide and antifolates. These approaches might help broaden the currently limited chemotherapeutic options of not only drug-resistant but also drug-susceptible tuberculosis, which still remains one of the most common infectious diseases in the developing world.

The structure of Enterococcus faecalis thymidylate synthase provides clues about folate bacterial metabolism

Drug resistance to therapeutic antibiotics poses a challenge to the identification of novel targets and drugs for the treatment of infectious diseases. Infections caused by Enterococcus faecalis are a major health problem. Thymidylate synthase (TS) from E. faecalis is a potential target for antibacterial therapy. The X-ray crystallographic structure of E. faecalis thymidylate synthase (EfTS), which was obtained as a native binary complex composed of EfTS and 5-formyltetrahydrofolate (5-FTHF), has been determined. The structure provides evidence that EfTS is a half-of-the-sites reactive enzyme, as 5-FTHF is bound to two of the four independent subunits present in the crystal asymmetric unit. 5-FTHF is a metabolite of the one-carbon transfer reaction catalysed by 5-formyltetrahydrofolate cyclo-ligase. Kinetic studies show that 5-FTHF is a weak inhibitor of EfTS, suggesting that the EfTS-5-FTHF complex may function as a source of folates and/or may regulate one-carbon metabolism. The structure represents the first example of endogenous 5-FTHF bound to a protein involved in folate metabolism.

Insights into the transposable mobilome of Paracoccus spp. (Alphaproteobacteria)

Several trap plasmids (enabling positive selection of transposition events) were used to identify a pool of functional transposable elements (TEs) residing in bacteria of the genus Paracoccus (Alphaproteobacteria). Complex analysis of 25 strains representing 20 species of this genus led to the capture and characterization of (i) 37 insertion sequences (ISs) representing 9 IS families (IS3, IS5, IS6, IS21, IS66, IS256, IS1182, IS1380 and IS1634), (ii) a composite transposon Tn6097 generated by two copies of the ISPfe2 (IS1634 family) containing two predicted genetic modules, involved in the arginine deiminase pathway and daunorubicin/doxorubicin resistance, (iii) 3 non-composite transposons of the Tn3 family, including Tn5393 carrying streptomycin resistance and (iv) a transposable genomic island TnPpa1 (45 kb). Some of the elements (e.g. Tn5393, Tn6097 and ISs of the IS903 group of the IS5 family) were shown to contain strong promoters able to drive transcription of genes placed downstream of the target site of transposition. Through the application of trap plasmid pCM132TC, containing a promoterless tetracycline resistance reporter gene, we identified five ways in which transposition can supply promoters to transcriptionally silent genes. Besides highlighting the diversity and specific features of several TEs, the analyses performed in this study have provided novel and interesting information on (i) the dynamics of the process of transposition (e.g. the unusually high frequency of transposition of TnPpa1) and (ii) structural changes in DNA mediated by transposition (e.g. the generation of large deletions in the recipient molecule upon transposition of ISPve1 of the IS21 family). We also demonstrated the great potential of TEs and transposition in the generation of diverse phenotypes as well as in the natural amplification and dissemination of genetic information (of adaptative value) by horizontal gene transfer, which is considered the driving force of bacterial evolution.