Naturally occurring amino acids differentially influence the development of Chlamydia trachomatis and Chlamydia (Chlamydophila) pneumoniae

Supplementation of lactobacillus-fermented rapeseed meal in broiler diet reduces Campylobacter jejuni cecal colonization and limits the l-tryptophan and l-histidine biosynthesis pathways

BACKGROUND

Campylobacter jejuni (C. jejuni), a widely distributed global foodborne pathogen, primarily linked with contaminated chicken meat, poses a significant health risk. Reducing the abundance of this pathogen in poultry meat is challenging but essential. This study assessed the impact of Lactobacillus-fermented rapeseed meal (LFRM) on broilers exposed to C. jejuni-contaminated litter, evaluating growth performance, Campylobacter levels, and metagenomic profile.

RESULTS

By day 35, the litter contamination successfully colonized broilers with Campylobacter spp., particularly C. jejuni. In the grower phase, LFRM improved (P < 0.05) body weight and daily weight gain, resulting in a 9.2% better feed conversion ratio during the pre-challenge period (the period before artificial infection; days 13-20). The LFRM also reduced the C. jejuni concentration in the ceca (P < 0.05), without altering alpha and beta diversity. However, metagenomic data analysis revealed LFRM targeted a reduction in the abundance of C. jejuni biosynthetic pathways of l-tryptophan and l-histidine and gene families associated with transcription and virulence factors while also possibly leading to selected stress-induced resistance mechanisms.

CONCLUSION

The study demonstrated that LFRM inclusion improved growth and decreased cecal Campylobacter spp. concentration and the relative abundance of pivotal C. jejuni genes. Performance benefits likely resulted from LFRM metabolites. At the molecular level, LFRM may have reduced C. jejuni colonization, likely by decreasing the abundance of energy transduction and l-histidine and l-tryptophan biosynthesis genes otherwise required for bacterial survival and increased virulence. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Serine deamination by human serine racemase synergizes with antibiotics to curtail the replication of Chlamydia trachomatis

The obligate intracellular bacterium, Chlamydia trachomatis, has evolved to depend on its human host for many metabolites, including most amino acids and three of the four nucleotides. Given this, it is not surprising that depletion of a single amino acid in the host cell growth medium blocks chlamydial replication. Paradoxically, supra-normal levels of some amino acids also block productive replication of Chlamydia. Here, we have determined how elevated serine levels, generated by exogenous supplementation, impede chlamydial inclusion development and reduce the generation of infectious progeny. Our findings reveal that human serine racemase, which is broadly expressed in multiple tissues, potentiates the anti-chlamydial effect of elevated serine concentrations. In addition to reversibly converting l-serine to d-serine, serine racemase also deaminates serine via β-elimination. We have determined that d-serine does not directly impact Chlamydia; rather, ammonia generated by serine deamination limits the productive chlamydial replication. Our findings imply that ammonia produced within host cells can traverse the chlamydial inclusion membrane. Further, this property of serine deaminase can be exploited to sensitize Chlamydia to concentrations of doxycycline that are otherwise not bactericidal. Because exogenously elevated levels of serine can be tolerated over extended periods, the broad expression pattern of serine racemase indicates it to be a host enzyme whose activity can be directed against multiple intracellular bacterial pathogens. From a therapeutic perspective, demonstrating host metabolism can be skewed to generate an anti-bacterial metabolite that synergizes with antibiotics, we believe our results provide a new approach to target intracellular pathogens.

Rv2231c, a unique histidinol phosphate aminotransferase from Mycobacterium tuberculosis, supports virulence by inhibiting host-directed defense

Nitrogen metabolism of M. tuberculosis is critical for its survival in infected host cells. M. tuberculosis has evolved sophisticated strategies to switch between de novo synthesis and uptake of various amino acids from host cells for metabolic demands. Pyridoxal phosphate-dependent histidinol phosphate aminotransferase-HspAT enzyme is critically required for histidine biosynthesis. HspAT is involved in metabolic synthesis of histidine, phenylalanine, tyrosine, tryptophan, and novobiocin. We showed that M. tuberculosis Rv2231c is a conserved enzyme with HspAT activity. Rv2231c is a monomeric globular protein that contains α-helices and β-sheets. It is a secretory and cell wall-localized protein that regulates critical pathogenic attributes. Rv2231c enhances the survival and virulence of recombinant M. smegmatis in infected RAW264.7 macrophage cells. Rv2231c is recognized by the TLR4 innate immune receptor and modulates the host immune response by suppressing the secretion of the antibacterial pro-inflammatory cytokines TNF, IL-12, and IL-6. It also inhibits the expression of co-stimulatory molecules CD80 and CD86 along with antigen presenting molecule MHC-I on macrophage and suppresses reactive nitrogen species formation, thereby promoting M2 macrophage polarization. Recombinant M. smegmatis expressing Rv2231c inhibited apoptosis in macrophages, promoting efficient bacterial survival and proliferation, thereby increasing virulence. Our results indicate that Rv2231c is a moonlighting protein that regulates multiple functions of M. tuberculosis pathophysiology to increase its virulence. These mechanistic insights can be used to better understand the pathogenesis of M. tuberculosis and to design strategies for tuberculosis mitigation.

Natural Clearance of Chlamydia trachomatis Infection Is Associated With Distinct Differences in Cervicovaginal Metabolites

BACKGROUND

Natural clearance of Chlamydia trachomatis in women occurs in the interval between screening and treatment. In vitro, interferon-γ (IFN-γ)-mediated tryptophan depletion results in C. trachomatis clearance, but whether this mechanism occurs in vivo remains unclear. We previously found that women who naturally cleared C. trachomatis had lower cervicovaginal levels of tryptophan and IFN-γ compared to women with persisting infection, suggesting IFN-γ-independent pathways may promote C. trachomatis clearance.

METHODS

Cervicovaginal lavages from 34 women who did (n = 17) or did not (n = 17) naturally clear C. trachomatis were subjected to untargeted high-performance liquid chromatography mass-spectrometry to identify metabolites and metabolic pathways associated with natural clearance.

RESULTS

In total, 375 positively charged metabolites and 149 negatively charged metabolites were annotated. Compared to women with persisting infection, C. trachomatis natural clearance was associated with increased levels of oligosaccharides trehalose, sucrose, melezitose, and maltotriose, and lower levels of indoline and various amino acids. Metabolites were associated with valine, leucine, and isoleucine biosynthesis pathways.

CONCLUSIONS

The cervicovaginal metabolome in women who did or did not naturally clear C. trachomatis is distinct. In women who cleared C. trachomatis, depletion of various amino acids, especially valine, leucine, and isoleucine, suggests that amino acids other than tryptophan impact C. trachomatis survival in vivo.

A Member of an Ancient Family of Bacterial Amino Acids Transporters Contributes to Chlamydia Nutritional Virulence and Immune Evasion

Many obligate intracellular bacteria, including members of the genus Chlamydia, cannot synthesize a variety of amino acids de novo and acquire these from host cells via largely unknown mechanisms. Previously, we determined that a missense mutation in ctl0225, a conserved Chlamydia open reading frame of unknown function, mediated sensitivity to interferon gamma. Here, we show evidence that CTL0225 is a member of the SnatA family of neutral amino acid transporters that contributes to the import of several amino acids into Chlamydia cells. Further, we show that CTL0225 orthologs from two other distantly related obligate intracellular pathogens (Coxiella burnetii and Buchnera aphidicola) are sufficient to import valine into Escherichia coli. We also show that chlamydia infection and interferon exposure have opposing effects on amino acid metabolism, potentially explaining the relationship between CTL0225 and interferon sensitivity. Overall, we show that phylogenetically diverse intracellular pathogens use an ancient family of amino acid transporters to acquire host amino acids and provide another example of how nutritional virulence and immune evasion can be linked in obligate intracellular pathogens.

Nutrient Scarcity in a New Defined Medium Reveals Metabolic Resistance to Antibiotics in the Fish Pathogen Piscirickettsia salmonis

Extensive use of antibiotics has been the primary treatment for the Salmonid Rickettsial Septicemia, a salmonid disease caused by the bacterium Piscirickettsia salmonis. Occurrence of antibiotic resistance has been explored in various P. salmonis isolates using different assays; however, P. salmonis is a nutritionally demanding intracellular facultative pathogen; thus, assessing its antibiotic susceptibility with standardized and validated protocols is essential. In this work, we studied the pathogen response to antibiotics using a genomic, a transcriptomic, and a phenotypic approach. A new defined medium (CMMAB) was developed based on a metabolic model of P. salmonis. CMMAB was formulated to increase bacterial growth in nutrient-limited conditions and to be suitable for performing antibiotic susceptibility tests. Antibiotic resistance was evaluated based on a comprehensive search of antibiotic resistance genes (ARGs) from P. salmonis genomes. Minimum inhibitory concentration assays were conducted to test the pathogen susceptibility to antibiotics from drug categories with predicted ARGs. In all tested P. salmonis strains, resistance to erythromycin, ampicillin, penicillin G, streptomycin, spectinomycin, polymyxin B, ceftazidime, and trimethoprim was medium-dependent, showing resistance to higher antibiotic concentrations in the CMMAB medium. The mechanism for antibiotic resistance to ampicillin in the defined medium was further explored and was proven to be associated to a decrease in the bacterial central metabolism, including the TCA cycle, the pentose-phosphate pathway, energy production, and nucleotide metabolism, and it was not associated with decreased growth rate of the bacterium or with the expression of any predicted ARG. Our results suggest that nutrient scarcity plays a role in the bacterial antibiotic resistance, protecting against the detrimental effects of antibiotics, and thus, we propose that P. salmonis exhibits a metabolic resistance to ampicillin when growing in a nutrient-limited medium.

De novo histidine biosynthesis protects Mycobacterium tuberculosis from host IFN-γ mediated histidine starvation

Intracellular pathogens including Mycobacterium tuberculosis (Mtb) have evolved with strategies to uptake amino acids from host cells to fulfil their metabolic requirements. However, Mtb also possesses de novo biosynthesis pathways for all the amino acids. This raises a pertinent question- how does Mtb meet its histidine requirements within an in vivo infection setting? Here, we present a mechanism in which the host, by up-regulating its histidine catabolizing enzymes through interferon gamma (IFN-γ) mediated signalling, exerts an immune response directed at starving the bacillus of intracellular free histidine. However, the wild-type Mtb evades this host immune response by biosynthesizing histidine de novo, whereas a histidine auxotroph fails to multiply. Notably, in an IFN-γ^-/- mouse model, the auxotroph exhibits a similar extent of virulence as that of the wild-type. The results augment the current understanding of host-Mtb interactions and highlight the essentiality of Mtb histidine biosynthesis for its pathogenesis.

Chlamydia trachomatis Oligopeptide Transporter Performs Dual Functions of Oligopeptide Transport and Peptidoglycan Recycling

Peptidoglycan, the sugar-amino acid polymer that composes the bacterial cell wall, requires a significant expenditure of energy to synthesize and is highly immunogenic. To minimize the loss of an energetically expensive metabolite and avoid host detection, bacteria often recycle their peptidoglycan, transporting its components back into the cytoplasm, where they can be used for subsequent rounds of new synthesis. The peptidoglycan-recycling substrate binding protein (SBP) MppA, which is responsible for recycling peptidoglycan fragments in Escherichia coli, has not been annotated for most intracellular pathogens. One such pathogen, Chlamydia trachomatis, has a limited capacity to synthesize amino acids de novo and therefore must obtain oligopeptides from its host cell for growth. Bioinformatics analysis suggests that the putative C. trachomatis oligopeptide transporter OppABCDF (OppABCDF _Ct ) encodes multiple SBPs (OppA1 _Ct , OppA2 _Ct , and OppA3 _Ct ). Intracellular pathogens often encode multiple SBPs, while only one, OppA, is encoded in the E. coli opp operon. We hypothesized that the putative OppABCDF transporter of C. trachomatis functions in both oligopeptide transport and peptidoglycan recycling. We coexpressed the putative SBP genes (oppA1_Ct , oppA2_Ct , oppA3_Ct ) along with oppBCDF_Ct in an E. coli mutant lacking the Opp transporter and determined that all three chlamydial OppA subunits supported oligopeptide transport. We also demonstrated the in vivo functionality of the chlamydial Opp transporter in C. trachomatis Importantly, we found that one chlamydial SBP, OppA3 _Ct , possessed dual substrate recognition properties and is capable of transporting peptidoglycan fragments (tri-diaminopimelic acid) in E. coli and in C. trachomatis These findings suggest that Chlamydia evolved an oligopeptide transporter to facilitate the acquisition of oligopeptides for growth while simultaneously reducing the accumulation of immunostimulatory peptidoglycan fragments in the host cell cytosol. The latter property reflects bacterial pathoadaptation that dampens the host innate immune response to Chlamydia infection.

Genomewide Transcriptional Responses of Iron-Starved Chlamydia trachomatis Reveal Prioritization of Metabolic Precursor Synthesis over Protein Translation

By utilizing an experimental approach that monitors the immediate global response of Chlamydia trachomatis to iron starvation, clues to long-standing issues in Chlamydia biology are revealed, including how Chlamydia adapts to this stress. We determined that this pathogen initiates a transcriptional program that prioritizes replenishment of nutrient stores over replication, possibly in preparation for rapid growth once optimal iron levels are restored. Transcription of genes for biosynthesis of metabolic precursors was generally upregulated, while those involved in multiple steps of translation were downregulated. We also observed an increase in transcription of genes involved in DNA repair and neutralizing oxidative stress, indicating that Chlamydia employs an “all-or-nothing” strategy. Its small genome limits its ability to tailor a specific response to a particular stress. Therefore, the “all-or-nothing” strategy may be the most efficient way of surviving within the host, where the pathogen likely encounters multiple simultaneous immunological and nutritional insults.

Iron is essential for growth and development of Chlamydia. Its long-term starvation in cultured mammalian cells leads to production of aberrant noninfectious chlamydial forms, also known as persistence. Immediate transcriptional responses to iron limitation have not been characterized, leaving a knowledge gap of how Chlamydia regulates its response to changes in iron availability. We used the fast-chelating agent 2,2′-bipyridyl (BPDL) to homogeneously starve Chlamydia trachomatis serovar L2 of iron, starting at 6 or 12 h postinfection. Immediate transcriptional responses were monitored after only 3 or 6 h of BPDL treatment, well before formation of aberrant Chlamydia. The first genomewide transcriptional response of C. trachomatis to iron starvation was subsequently determined utilizing RNA sequencing. Only 7% and 8% of the genome were differentially expressed in response to iron starvation at the early and middle stages of development, respectively. Biological pathway analysis revealed an overarching theme. Synthesis of macromolecular precursors (deoxynucleotides, amino acids, charged tRNAs, and acetyl coenzyme A [acetyl-CoA]) was upregulated, while energy-expensive processes (ABC transport and translation) were downregulated. A large fraction of differentially downregulated genes are involved in translation, including those encoding ribosome assembly and initiation and termination factors, which could be analogous to the translation downregulation triggered by stress in other prokaryotes during stringent responses. Additionally, transcriptional upregulation of DNA repair, oxidative stress, and tryptophan salvage genes reveals a possible coordination of responses to multiple antimicrobial and immunological insults. These responses of replicative-phase Chlamydia to iron starvation indicate a prioritization of survival over replication, enabling the pathogen to “stock the pantry” with ingredients needed for rapid growth once optimal iron levels are restored.

IMPORTANCE By utilizing an experimental approach that monitors the immediate global response of Chlamydia trachomatis to iron starvation, clues to long-standing issues in Chlamydia biology are revealed, including how Chlamydia adapts to this stress. We determined that this pathogen initiates a transcriptional program that prioritizes replenishment of nutrient stores over replication, possibly in preparation for rapid growth once optimal iron levels are restored. Transcription of genes for biosynthesis of metabolic precursors was generally upregulated, while those involved in multiple steps of translation were downregulated. We also observed an increase in transcription of genes involved in DNA repair and neutralizing oxidative stress, indicating that Chlamydia employs an “all-or-nothing” strategy. Its small genome limits its ability to tailor a specific response to a particular stress. Therefore, the “all-or-nothing” strategy may be the most efficient way of surviving within the host, where the pathogen likely encounters multiple simultaneous immunological and nutritional insults.

Genomic factors related to tissue tropism in Chlamydia pneumoniae infection

BACKGROUND

Chlamydia pneumoniae (Cpn) are obligate intracellular bacteria that cause acute infections of the upper and lower respiratory tract and have been implicated in chronic inflammatory diseases. Although of significant clinical relevance, complete genome sequences of only four clinical Cpn strains have been obtained. All of them were isolated from the respiratory tract and shared more than 99% sequence identity. Here we investigate genetic differences on the whole-genome level that are related to Cpn tissue tropism and pathogenicity.

RESULTS

We have sequenced the genomes of 18 clinical isolates from different anatomical sites (e.g. lung, blood, coronary arteries) of diseased patients, and one animal isolate. In total 1,363 SNP loci and 184 InDels have been identified in the genomes of all clinical Cpn isolates. These are distributed throughout the whole chlamydial genome and enriched in highly variable regions. The genomes show clear evidence of recombination in at least one potential region but no phage insertions. The tyrP gene was always encoded as single copy in all vascular isolates. Phylogenetic reconstruction revealed distinct evolutionary lineages containing primarily non-respiratory Cpn isolates. In one of these, clinical isolates from coronary arteries and blood monocytes were closely grouped together. They could be distinguished from all other isolates by characteristic nsSNPs in genes involved in RB to EB transition, inclusion membrane formation, bacterial stress response and metabolism.

CONCLUSIONS

This study substantially expands the genomic data of Cpn and elucidates its evolutionary history. The translation of the observed Cpn genetic differences into biological functions and the prediction of novel pathogen-oriented diagnostic strategies have to be further explored.

Human enteroendocrine cell responses to infection with Chlamydia trachomatis: a microarray study

Background

Enteroendocrine cells (EEC) are highly specialized cells producing signalling molecules vital to the normal functions of the gut. Recently, we showed altered protein distribution in Chlamydia infected EEC in vitro. The aim of this study was to perform a microarray analysis of the response pattern of EEC from both large and small bowel to infection in vitro, using Chlamydia trachomatis infection as a model.

Methods

Two human EEC lines: LCC-18, derived from a neuroendocrine colonic tumour, and CNDT-2, derived from a small intestinal carcinoid, were infected using cultured C. trachomatis serovar LGV II strain 434 (ATCC VR-902B). Penicillin G was used to induce persistent infection. We used microarray analysis (Affymetrix GeneChip®) for studying changes in gene expression at different stages of infection.

Results

Twenty-four hours after active and persistent infection, 66 and 411 genes in LCC-18 and 68 and 170 genes in CNDT-2 cells, respectively showed mean expression ratios >2-fold compared to non-infected cells. These genes encoded factors regulating apoptosis, cell differentiation, transcription regulation, cytokine activity, amine biosynthesis and vesicular transport. We found significant differences in gene transcription levels between persistently infected and non-infected cells in 10 genes coding for different solute carrier transporters (SLC) and in 5 genes related to endocrine function (GABARAPL1, GRIP1, DRD2, SYT5 and SYT7).

Conclusions

Infected EEC cells exhibit cell-type specific patterns related to vesicular transport, secretion and neurotransmitters. EEC play a pivotal role in regulation of gut motility and an impairment of enteroendocrine function can contribute to motility disorders.

Evolution to a chronic disease niche correlates with increased sensitivity to tryptophan availability for the obligate intracellular bacterium Chlamydia pneumoniae

The chlamydiae are obligate intracellular parasites that have evolved specific interactions with their various hosts and host cell types to ensure their successful survival and consequential pathogenesis. The species Chlamydia pneumoniae is ubiquitous, with serological studies showing that most humans are infected at some stage in their lifetime. While most human infections are asymptomatic, C. pneumoniae can cause more-severe respiratory disease and pneumonia and has been linked to chronic diseases such as asthma, atherosclerosis, and even Alzheimer's disease. The widely dispersed animal-adapted C. pneumoniae strains cause an equally wide range of diseases in their hosts. It is emerging that the ability of C. pneumoniae to survive inside its target cells, including evasion of the host's immune attack mechanisms, is linked to the acquisition of key metabolites. Tryptophan and arginine are key checkpoint compounds in this host-parasite battle. Interestingly, the animal strains of C. pneumoniae have a slightly larger genome, enabling them to cope better with metabolite restrictions. It therefore appears that as the evolutionarily more ancient animal strains have evolved to infect humans, they have selectively become more "susceptible" to the levels of key metabolites, such as tryptophan. While this might initially appear to be a weakness, it allows these human C. pneumoniae strains to exquisitely sense host immune attack and respond by rapidly reverting to a persistent phase. During persistence, they reduce their metabolic levels, halting progression of their developmental cycle, waiting until the hostile external conditions have passed before they reemerge.

Raman microspectroscopy reveals long-term extracellular activity of Chlamydiae

The phylum Chlamydiae consists exclusively of obligate intracellular bacteria. Some of them are formidable pathogens of humans, while others occur as symbionts of amoebae. These genetically intractable bacteria possess a developmental cycle consisting of replicative reticulate bodies and infectious elementary bodies, which are believed to be physiologically inactive. Confocal Raman microspectroscopy was applied to differentiate between reticulate bodies and elementary bodies of Protochlamydia amoebophila and to demonstrate in situ the labelling of this amoeba symbiont after addition of isotope-labelled phenylalanine. Unexpectedly, uptake of this amino acid was also observed for both developmental stages for up to 3 weeks, if incubated extracellularly with labelled phenylalanine, and P. amoebophila remained infective during this period. Furthermore, P. amoebophila energizes its membrane and performs protein synthesis outside of its host. Importantly, amino acid uptake and protein synthesis after extended extracellular incubation could also be demonstrated for the human pathogen Chlamydia trachomatis, which synthesizes stress-related proteins under these conditions as shown by 2-D gel electrophoresis and MALDI-TOF/TOF mass spectrometry. These findings change our perception of chlamydial biology and reveal that host-free analyses possess a previously not recognized potential for direct experimental access to these elusive microorganisms.

Long-term effects of natural amino acids on infection with Chlamydia trachomatis

Supplementation of culture media with leucine, isoleucine, methionine, or phenylalanine was previously found to inhibit Chlamydia trachomatis growth in HEp-2 cells. Here, we investigated the long-term effects of these additives on C. trachomatis infection in the same cell model. Amino acid addition 30h post-infection (pi) effectively suppressed the generation of infectious progeny monitored for 10 days pi. With the exception of phenylalanine, amino acid treatment beginning at 2h pi for up to 15 days led to a complete lack of infectious progeny. Phenylalanine treatment resulted in residual minimal infectivity. In extended supplementation experiments, very small aberrant chlamydial inclusions formed, whose numbers decreased considerably over time, and the production of infectious chlamydiae could not be rescued even upon amino acid withdrawal. Interestingly, a state of chlamydial persistence was induced under these conditions, as 16S rRNA transcripts were detected throughout treatment. However, expression of several key chlamydial genes including omp1, groEL, omcB, and those functioning for chlamydial DNA replication and cytokinesis was generally very low or even undetected, particularly in monolayers treated with Leu, Ile, or Met. These data revealed a capacity of certain amino acids to eliminate infectious chlamydial progeny. Additionally, supplementation of certain amino acids resulted in the formation of a small persistent population. Extrapolating from these findings may help formulate an anti-chlamydial treatment based on nutritional elements.

Competitive inhibition of amino acid uptake suppresses chlamydial growth: involvement of the chlamydial amino acid transporter BrnQ

Chlamydiaceae are obligate intracellular bacterial pathogens that strictly depend on host metabolites, such as nucleotides, lipids, and amino acids. Depletion of amino acids in cell culture media results in abnormal chlamydial development in vitro. Surprisingly, enrichment of certain amino acids also retards chlamydial growth. Our experiments revealed that the antichlamydial effects are largely independent of changes in the host cell transcriptome or proteome and in the major signal transduction pathway modulated by amino acids, the mTOR (mammalian target of rapamycin) pathway. Furthermore, the chlamydial growth inhibition induced by leucine, isoleucine, methionine, or phenylalanine was completely reversed by concomitant addition of valine. In contrast, the growth inhibition induced by serine, glycine, or threonine was not reversed by valine addition. Functional characterization of the only predicted chlamydial transporter for branched-chain amino acids, BrnQ, revealed that it can be blocked by leucine, isoleucine, methionine, or phenylalanine but not by serine, glycine, or threonine. This chlamydial transporter is the only known BrnQ homolog possessing specificity for methionine, suggesting a unique strategy for methionine uptake among gram-negative bacteria. The antichlamydial effects of leucine, isoleucine, methionine, and phenylalanine could be explained as competitive inhibition of the BrnQ transporter and subsequent valine starvation.

Characterization of an acid-dependent arginine decarboxylase enzyme from Chlamydophila pneumoniae

Genome sequences from members of the Chlamydiales encode diverged homologs of a pyruvoyl-dependent arginine decarboxylase enzyme that nonpathogenic euryarchaea use in polyamine biosynthesis. The Chlamydiales lack subsequent genes required for polyamine biosynthesis and probably obtain polyamines from their host cells. To identify the function of this protein, the CPn1032 homolog from the respiratory pathogen Chlamydophila pneumoniae was heterologously expressed and purified. This protein self-cleaved to form a reactive pyruvoyl group, and the subunits assembled into a thermostable (alphabeta)(3) complex. The mature enzyme specifically catalyzed the decarboxylation of L-arginine, with an unusually low pH optimum of 3.4. The CPn1032 gene complemented a mutation in the Escherichia coli adiA gene, which encodes a pyridoxal 5'-phosphate-dependent arginine decarboxylase, restoring arginine-dependent acid resistance. Acting together with a putative arginine-agmatine antiporter, the CPn1032 homologs may have evolved convergently to form an arginine-dependent acid resistance system. These genes are the first evidence that obligately intracellular chlamydiae may encounter acidic conditions. Alternatively, this system could reduce the host cell arginine concentration and produce inhibitors of nitric oxide synthase.