Amino acids as nutritional factors and (p)ppGpp as an alarmone of the stringent response regulate natural transformation in Micrococcus luteus

Integrated multi-omics reveals metabolic determinants of CRAB ST2 airway infection progression

Acinetobacter baumannii commonly causes lower airway colonization and infection and is easily confused. This study aimed to analyze the biological characteristics of carbapenem-resistant A. baumannii (CRAB) ST2 in the lower airway and identify an effective method for distinguishing between A. baumannii colonization and infection. Lower airway CRAB ST2 isolated at the Department of Respiratory and Critical Care Medicine and intensive care unit of our hospital from January 2021 to June 2023 were included, and their whole genome, biofilm-forming ability, bacterial virulence, and metabolome were analyzed. Fifty-six strains of CRAB with ST2 were identified, of which 32 were infection strains and 24 were colonization strains. The virulence and resistance genes, as well as the virulence and biofilm-forming ability, of ST2-type carbapenem-resistant lower airway infecting and colonizing A. baumannii strains were similar. The levels of metabolites were significantly lower in ST2-type carbapenem-resistant lower airway-infecting A. baumannii infection strains than those in the lower airway-colonizing strains. The levels of (S)-(+)-2-(aniline methyl) pyrrolidine, valine, ketoleucine, L-isoleucine, homoserine, N-acetyl-L-aspartate, and 2-aminoethanol-1-phosphate in the lower airway infection strains were significantly lower than those in the lower airway colonization strains. Bacterial virulence tests and biofilm formation ability could not distinguish the same ST of CRAB in the lower airway from the colonization or infection strains; however, metabolomics could. The biosynthesis and degradation pathways of valine, leucine, and isoleucine were downregulated, and changes in their metabolism may be important factors in promoting carbapenem-resistant A. baumanniiCRAB transformation from colonization to infection.IMPORTANCECarbapenem-resistant A. baumannii (CRAB) poses a critical threat in clinical settings, particularly due to challenges in distinguishing airway colonization from active infection, which complicates treatment decisions. This study highlights the limitations of conventional approaches-such as virulence gene profiling, phenotypic virulence assays, and biofilm formation analysis-in differentiating CRAB ST2 strains isolated from lower airway infections versus colonization. By integrating metabolomics, we identified distinct metabolic signatures linked to infection, including significant downregulation of valine, leucine, and isoleucine biosynthesis/degradation pathways and reduced levels of key metabolites (e.g., ketoleucine and L-isoleucine) in infection strains. These findings provide the first evidence that metabolic dysregulation may drive CRAB's transition from colonization to invasive disease. This work advances our understanding of CRAB pathogenicity and offers a novel, metabolism-based strategy to improve diagnostic accuracy, guide targeted therapies, and optimize antimicrobial stewardship in managing CRAB-associated respiratory infections.

Effect of Light Regime on Candidatus Puniceispirillum marinum IMCC1322 in Nutrient-Replete Conditions

Previous studies showed no improvement in bacterial biomass for Candidatus Puniceispirillum marinum IMCC1322 under light regimes. Nevertheless, in nutrient-replete cultures with higher inoculating cell densities, strain IMCC1322 exhibited proteorhodopsin photoheterotrophy. Increasing both inoculum size and the amino acid pool can eliminate quorum sensing and starvation responses in strain IMCC1322. Light regimes affected IMCC1322 cultures in stationary/death phases, where cellular ATP levels ranged from 0.0331 to 1.74 mM, with ATP/cell ranging from 13.9 to 367 zeptomoles. In nutrient-depleted conditions, strain IMCC1322 may suffer from excessive protons generated by proteorhodopsin under light conditions. IMCC1322 may tolerate excessive periplasmic protons through ATP-dependent proton pumping and protonation of augmented amino acids. Meanwhile, acid stress could also be mitigated by refining membrane permeability through unsaturation and cyclopropanation of phospholipids. Oceanic bacteria such as IMCC1322 and SAR11 preferred anaplerotic TCA cycles over glycolysis and rely on the Entner-Doudoroff (ED) pathway for growth. Although ATP generation is less efficient in the ED pathway, it offers advantages during rapid growth owing to its strong thermodynamic driving force. The metabolism of IMCC1322 favors gluconeogenesis over glycolysis, aligning with the metabolism of SAR11 reported in previous studies. However, the additional light-driven, PR-dependent ATP synthesis in IMCC1322 is expected to be insufficient to support protein turnover after the log phase, as well as in nutrient-limited conditions. Stable isotope measurements showed no significant differences in the inorganic carbon assimilation between constant light and constant dark cultures in late log phase.

The complex regulation of competence in Staphylococcus aureus under microaerobic conditions

To perform natural transformation, one of the three main Horizontal Gene Transfer mechanisms, bacteria need to enter a physiological differentiated state called genetic competence. Interestingly, new bacteria displaying such aptitude are often discovered, and one of the latest is the human pathogen Staphylococcus aureus.Here, we show an optimized protocol, based on planktonic cells cultures, leading to a large percentage of the population activating the development of competence and a significant improvement of S. aureus natural transformation efficiencies. Taking advantage of these conditions, we perform transcriptomics analyses to characterize the regulon of each central competence regulator. SigH and ComK1 are both found essential for activating natural transformation genes but also important for activation or repression of peripheral functions. Even though ComK2 is not found important for the control of transformation genes, its regulon shows an important overlap with that of SigH and ComK1. Finally, we propose that microaerobic conditions, sensed by the SrrAB two-component system, are key to activate competence in S. aureus.

Isopropyl Amino Acid Esters Ionic Liquids as Vehicles for Non-Steroidal Anti-Inflammatory Drugs in Potential Topical Drug Delivery Systems with Antimicrobial Activity

New derivatives of non-steroidal anti-inflammatory drugs were synthesized via conjugation with L-amino acid isopropyl esters. The characteristics of the physicochemical properties of the obtained pharmaceutically active ionic liquids were determined. It has been shown how the incorporation of various L-amino acid esters as an ion pair affects the properties of the parent drug. Moreover, the antimicrobial activity of the obtained compounds was evaluated. The proposed structural modifications of commonly used drugs indicate great potential for use in topical and transdermal preparations.

The Spread of Antibiotic Resistance Genes In Vivo Model

Infections caused by antibiotic-resistant bacteria are a major public health threat. The emergence and spread of antibiotic resistance genes (ARGs) in the environment or clinical setting pose a serious threat to human and animal health worldwide. Horizontal gene transfer (HGT) of ARGs is one of the main reasons for the dissemination of antibiotic resistance in vitro and in vivo environments. There is a consensus on the role of mobile genetic elements (MGEs) in the spread of bacterial resistance. Most drug resistance genes are located on plasmids, and the spread of drug resistance genes among microorganisms through plasmid-mediated conjugation transfer is the most common and effective way for the spread of multidrug resistance. Experimental studies of the processes driving the spread of antibiotic resistance have focused on simple in vitro model systems, but the current in vitro protocols might not correctly reflect the HGT of antibiotic resistance genes in realistic conditions. This calls for better models of how resistance genes transfer and disseminate in vivo. The in vivo model can better mimic the situation that occurs in patients, helping study the situation in more detail. This is crucial to develop innovative strategies to curtail the spread of antibiotic resistance genes in the future. This review aims to give an overview of the mechanisms of the spread of antibiotic resistance genes and then demonstrate the spread of antibiotic resistance genes in the in vivo model. Finally, we discuss the challenges in controlling the spread of antibiotic resistance genes and their potential solutions.

Identification of New Chromosomal Loci Involved in com Genes Expression and Natural Transformation in the Actinobacterial Model Organism Micrococcus luteus

Historically, Micrococcus luteus was one of the first organisms used to study natural transformation, one of the main routes of horizontal gene transfer among prokaryotes. However, little is known about the molecular basis of competence development in M. luteus or any other representative of the phylum of high-GC Gram-positive bacteria (Actinobacteria), while this means of genetic exchange has been studied in great detail in Gram-negative and low-GC Gram-positive bacteria (Firmicutes). In order to identify new genetic elements involved in regulation of the comEA-comEC competence operon in M. luteus, we conducted random chemical mutagenesis of a reporter strain expressing lacZ under the control of the comEA-comEC promoter, followed by the screening of dysregulated mutants. Mutants with (i) upregulated com promoter under competence-repressing conditions and (ii) mutants with a repressed com promoter under competence-inducing conditions were isolated. After genotype and phenotype screening, the genomes of several mutant strains were sequenced. A selection of putative com-influencing mutations was reinserted into the genome of the M. luteus reporter strain as markerless single-nucleotide mutations to confirm their effect on com gene expression. This strategy revealed mutations affecting com gene expression at genetic loci different from previously known genes involved in natural transformation. Several of these mutations decreased transformation frequencies by several orders of magnitude, thus indicating significant roles in competence development or DNA acquisition in M. luteus. Among the identified loci, there was a new locus containing genes with similarity to genes of the tad clusters of M. luteus and other bacteria.