Andreas Haag
@research-portal.st-andrews.ac.uk
Lecturer Infection and Global Health
University of St Andrews
Scopus Publications
Scholar Citations
Scholar h-index
Scholar i10-index
Scopus Publications
Magdalena Podkowik, Andrew I Perault, Gregory Putzel, Andrew Pountain, Jisun Kim, Ashley L DuMont, Erin E Zwack, Robert J Ulrich, Theodora K Karagounis, Chunyi Zhou,et al.
eLife Sciences Publications, Ltd
The agr quorum-sensing system links Staphylococcus aureus metabolism to virulence, in part by increasing bacterial survival during exposure to lethal concentrations of H2O2, a crucial host defense against S. aureus. We now report that protection by agr surprisingly extends beyond post-exponential growth to the exit from stationary phase when the agr system is no longer turned on. Thus, agr can be considered a constitutive protective factor. Deletion of agr resulted in decreased ATP levels and growth, despite increased rates of respiration or fermentation at appropriate oxygen tensions, suggesting that Δagr cells undergo a shift towards a hyperactive metabolic state in response to diminished metabolic efficiency. As expected from increased respiratory gene expression, reactive oxygen species (ROS) accumulated more in the agr mutant than in wild-type cells, thereby explaining elevated susceptibility of Δagr strains to lethal H2O2 doses. Increased survival of wild-type agr cells during H2O2 exposure required sodA, which detoxifies superoxide. Additionally, pretreatment of S. aureus with respiration-reducing menadione protected Δagr cells from killing by H2O2. Thus, genetic deletion and pharmacologic experiments indicate that agr helps control endogenous ROS, thereby providing resilience against exogenous ROS. The long-lived ‘memory’ of agr-mediated protection, which is uncoupled from agr activation kinetics, increased hematogenous dissemination to certain tissues during sepsis in ROS-producing, wild-type mice but not ROS-deficient (Cybb−/−) mice. These results demonstrate the importance of protection that anticipates impending ROS-mediated immune attack. The ubiquity of quorum sensing suggests that it protects many bacterial species from oxidative damage.
Mohammed A. Thabet, José R. Penadés, and Andreas F. Haag
Springer Science and Business Media LLC
AbstractBacteriophages (phages) are the most abundant biological entities on Earth, exerting a significant influence on the dissemination of bacterial virulence, pathogenicity, and antimicrobial resistance. Temperate phages integrate into the bacterial chromosome in a dormant state through intricate regulatory mechanisms. These mechanisms repress lytic genes while facilitating the expression of integrase and the CI master repressor. Upon bacterial SOS response activation, the CI repressor undergoes auto-cleavage, producing two fragments with the N-terminal domain (NTD) retaining significant DNA-binding ability. The process of relieving CI NTD repression, essential for prophage induction, remains unknown. Here we show a specific interaction between the ClpX protease and CI NTD repressor fragment of phages Ф11 and 80α in Staphylococcus aureus. This interaction is necessary and sufficient for prophage activation after SOS-mediated CI auto-cleavage, defining the final stage in the prophage induction cascade. Our findings unveil unexpected roles of bacterial protease ClpX in phage biology.
Andreas F. Haag, Lassi Liljeroos, Paolo Donato, Clarissa Pozzi, Tarcisio Brignoli, Matthew J. Bottomley, Fabio Bagnoli, and Isabel Delany
American Society for Microbiology
Vaccination is an attractive strategy for preventing bacterial infections in an age of increased antimicrobial resistance. However, vaccine development frequently suffers significant setbacks when candidate antigens that show promising results in in vitro experimentation fail to protect from disease.
Sara Borghi, Ana Antunes, Andreas F. Haag, Marco Spinsanti, Tarcisio Brignoli, Enea Ndoni, Vincenzo Scarlato, and Isabel Delany
MDPI AG
Neisseria meningitidis colonizes the nasopharynx of humans, and pathogenic strains can disseminate into the bloodstream, causing septicemia and meningitis. NHBA is a surface-exposed lipoprotein expressed by all N. meningitidis strains in different isoforms. Diverse roles have been reported for NHBA in heparin-mediated serum resistance, biofilm formation, and adherence to host tissues. We determined that temperature controls the expression of NHBA in all strains tested, with increased levels at 30–32 °C compared to 37 °C. Higher NHBA expression at lower temperatures was measurable both at mRNA and protein levels, resulting in higher surface exposure. Detailed molecular analysis indicated that multiple molecular mechanisms are responsible for the thermoregulated NHBA expression. The comparison of mRNA steady-state levels and half-lives at 30 °C and 37 °C demonstrated an increased mRNA stability/translatability at lower temperatures. Protein stability was also impacted, resulting in higher NHBA stability at lower temperatures. Ultimately, increased NHBA expression resulted in higher susceptibility to complement-mediated killing. We propose that NHBA regulation in response to temperature downshift might be physiologically relevant during transmission and the initial step(s) of interaction within the host nasopharynx. Together these data describe the importance of NHBA both as a virulence factor and as a vaccine antigen during neisserial colonization and invasion.
Rodrigo Ibarra-Chávez, Aisling Brady, John Chen, José R. Penadés, and Andreas F. Haag
Public Library of Science (PLoS)
Phage-inducible chromosomal islands (PICIs) are a widespread family of highly mobile genetic elements that disseminate virulence and toxin genes among bacterial populations. Since their life cycle involves induction by helper phages, they are important players in phage evolution and ecology. PICIs can interfere with the lifecycle of their helper phages at different stages resulting frequently in reduced phage production after infection of a PICI-containing strain. Since phage defense systems have been recently shown to be beneficial for the acquisition of exogenous DNA via horizontal gene transfer, we hypothesized that PICIs could provide a similar benefit to their hosts and tested the impact of PICIs in recipient strains on host cell viability, phage propagation and transfer of genetic material. Here we report an important role for PICIs in bacterial evolution by promoting the survival of phage-mediated transductants of chromosomal or plasmid DNA. The presence of PICIs generates favorable conditions for population diversification and the inheritance of genetic material being transferred, such as antibiotic resistance and virulence genes. Our results show that by interfering with phage reproduction, PICIs can protect the bacterial population from phage attack, increasing the overall survival of the bacterial population as well as the transduced cells. Moreover, our results also demonstrate that PICIs reduce the frequency of lysogenization after temperate phage infection, creating a more genetically diverse bacterial population with increased bet-hedging opportunities to adapt to new niches. In summary, our results identify a new role for the PICIs and highlight them as important drivers of bacterial evolution.
Suzanne Humphrey, Alfred Fillol-Salom, Nuria Quiles-Puchalt, Rodrigo Ibarra-Chávez, Andreas F. Haag, John Chen, and José R. Penadés
Springer Science and Business Media LLC
AbstractIt is commonly assumed that the horizontal transfer of most bacterial chromosomal genes is limited, in contrast to the frequent transfer observed for typical mobile genetic elements. However, this view has been recently challenged by the discovery of lateral transduction in Staphylococcus aureus, where temperate phages can drive the transfer of large chromosomal regions at extremely high frequencies. Here, we analyse previously published as well as new datasets to compare horizontal gene transfer rates mediated by different mechanisms in S. aureus and Salmonella enterica. We find that the horizontal transfer of core chromosomal genes via lateral transduction can be more efficient than the transfer of classical mobile genetic elements via conjugation or generalized transduction. These results raise questions about our definition of mobile genetic elements, and the potential roles played by lateral transduction in bacterial evolution.
Andreas F. Haag, Magdalena Podkowik, Rodrigo Ibarra-Chávez, Francisca Gallego del Sol, Geeta Ram, John Chen, Alberto Marina, Richard P. Novick, and José R. Penadés
Springer Science and Business Media LLC
Gonzalo Yebra, Andreas F. Haag, Maan M. Neamah, Bryan A. Wee, Emily J. Richardson, Pilar Horcajo, Sander Granneman, María Ángeles Tormo-Más, Ricardo de la Fuente, J. Ross Fitzgerald,et al.
Public Library of Science (PLoS)
The emergence of new pathogens is a major threat to public and veterinary health. Changes in bacterial habitat such as a switch in host or disease tropism are typically accompanied by genetic diversification.Staphylococcus aureusis a multi-host bacterial species associated with human and livestock infections. A microaerophilic subspecies,Staphylococcus aureussubsp.anaerobius, is responsible for Morel’s disease, a lymphadenitis restricted to sheep and goats. However, the evolutionary history ofS.aureussubsp.anaerobiusand its relatedness toS.aureusare unknown. Population genomic analyses of clinicalS.aureussubsp.anaerobiusisolates revealed a highly conserved clone that descended from aS.aureusprogenitor about 1000 years ago before differentiating into distinct lineages that contain African and European isolates.S.aureussubsp.anaerobiushas undergone limited clonal expansion, with a restricted population size, and an evolutionary rate 10-fold slower thanS.aureus. The transition to its current restricted ecological niche involved acquisition of a pathogenicity island encoding a ruminant host-specific effector of abscess formation, large chromosomal re-arrangements, and the accumulation of at least 205 pseudogenes, resulting in a highly fastidious metabolism. Importantly, expansion of ~87 insertion sequences (IS) located largely in intergenic regions provided distinct mechanisms for the control of expression of flanking genes, including a novel mechanism associated with IS-mediated anti-anti-sense decoupling of ancestral gene repression. Our findings reveal the remarkable evolutionary trajectory of a host-restricted bacterial pathogen that resulted from extensive remodelling of theS.aureusgenome through an array of diverse mechanisms in parallel.
B. Rapun-Araiz, A. F. Haag, V. De Cesare, C. Gil, P. Dorado-Morales, J. R. Penades, and I. Lasa
American Society for Microbiology
Bacteria are able to sense environmental conditions and respond accordingly. Their sensorial system relies on pairs of sensory and regulatory proteins, known as two-component systems (TCSs). The majority of bacteria contain dozens of TCSs, each of them responsible for sensing and responding to a different range of signals. Traditionally, the function of each TCS has been determined by analyzing the changes in gene expression caused by the absence of individual TCSs. Here, we used a bacterial strain deprived of the complete TC sensorial system to introduce, one by one, the active form of every TCS. This gain-of-function strategy allowed us to identify the changes in gene expression conferred by each TCS without interference of other members of the family.
Beatriz Rapun-Araiz, Andreas F Haag, Cristina Solano, and Iñigo Lasa
Elsevier BV
Rodrigo Ibarra-Chávez, Andreas F. Haag, Pedro Dorado-Morales, Iñigo Lasa, and José R. Penadés
American Association for the Advancement of Science (AAAS)
Phage-inducible chromosomal islands (PICIs) are a widespread family of mobile genetic elements, which have an important role in bacterial pathogenesis. These elements mobilize among bacterial species at extremely high frequencies, representing an attractive tool for the delivery of synthetic genes. However, tools for their genetic manipulation are limited and timing consuming. Here, we have adapted a synthetic biology approach for rapidly editing of PICIs in Saccharomyces cerevisiae based on their ability to excise and integrate into the bacterial chromosome of their cognate host species. As proof of concept, we engineered several PICIs from Staphylococcus aureus and Escherichia coli and validated this methodology for the study of the biology of these elements by generating multiple and simultaneous mutations in different PICI genes. For biotechnological purposes, we also synthetically constructed PICIs as Trojan horses to deliver different CRISPR-Cas9 systems designed to either cure plasmids or eliminate cells carrying the targeted genes. Our results demonstrate that the strategy developed here can be employed universally to study PICIs and enable new approaches for diagnosis and treatment of bacterial diseases.
Andreas F. Haag and Peter Mergaert
Wiley
After infection of nodule host cells, Rhizobium bacteria differentiate into nitrogen fixing bacteroids. Depending on the host plant, this process can be reversible or alternatively terminal, after which bacteria can no longer replicate. Terminal bacteroid differentiation is controlled by the host plant and was first described in Medicago truncatula and other legumes in the inverted repeat-lacking clade to be dependent on a group of nodule-specific, cysteine-rich (NCR) peptides. Recent publications have shown that NCR-like peptides can also be found in other clades of legumes and that the host's armory of NCR peptides defines shape and degree of bacteroid differentiation. Terminal bacteroid differentiation is associated with a block of the bacterial cell division machinery and profound regulatory changes in the bacterial cell cycle. Several bacterial genes and proteins have been found to be of key importance for establishing a successful symbiotic interaction with NCR-producing hosts. The bacterial BacA protein was the first protein to be identified to be essential for bacterial survival within the host cell upon NCR challenge in IRLC legumes. However, recent studies have highlighted that BacA appears to be not essential for symbiosis with all NCR-producing legumes and alternative mechanisms can protect bacteria from NCR peptides. Particularly, rhizobia can actively promote the degradation of NCR peptides and thus escape terminal bacteroid differentiation, tilting the symbiotic relationship in their favor. Our understanding of the complex interlinked relationships of the NCR peptide imposed stop of bacterial replication and the mechanisms that rhizobia have evolved to survive and counter host restrictions is still only beginning. Here, we aim to give an overview on our current understanding of this symbiotic tug of war.
Kate L. Seib, Andreas F. Haag, Francesca Oriente, Laura Fantappiè, Sara Borghi, Evgeny A. Semchenko, Benjamin L. Schulz, Francesca Ferlicca, Anna Rita Taddei, Marzia M. Giuliani,et al.
Wiley
GNA2091 is one of the components of the 4‐component meningococcal serogroup B vaccine (4CMenB) vaccine and is highly conserved in all meningococcal strains. However, its functional role has not been fully characterized. Here we show that nmb2091 is part of an operon and is cotranscribed with the nmb2089, nmb2090, and nmb2092 adjacent genes, and a similar but reduced operon arrangement is conserved in many other gram‐negative bacteria. Deletion of the nmb2091 gene causes an aggregative phenotype with a mild defect in cell separation; differences in the outer membrane composition and phospholipid profile, in particular in the phosphoethanolamine levels; an increased level of outer membrane vesicles; and deregulation of the zinc‐responsive genes such as znuD. Finally, the Δ2091 strain is attenuated with respect to the wild‐type strain in competitive index experiments in the infant rat model of meningococcal infection. Altogether these data suggest that GNA2091 plays important roles in outer membrane architecture, biogenesis, homeostasis, and in meningococcal survival in vivo, and amodel for its role is discussed. These findings highlight the importance of GNA2091 as a vaccine component.—Seib, K. L., Haag, A. F., Oriente, F., Fantappiè, L., Borghi, S., Semchenko, E. A., Schulz, B. L., Ferlicca, F., Taddei, A. R., Giuliani, M. M., Pizza, M., Delany, I. The meningococcal vaccine antigen GNA2091 is an analogue of YraP and plays key roles in outer membrane stability and virulence. FASEB J. 33, 12324‐12335 (2019). www.fasebj.org
Andreas F. Haag, J. Ross Fitzgerald, and José R. Penadés
American Society for Microbiology
ABSTRACT Staphylococcus aureus is a mammalian commensal and opportunistic pathogen that colonizes niches such as skin, nares and diverse mucosal membranes of about 20-30% of the human population. S. aureus can cause a wide spectrum of diseases in humans and both methicillin-sensitive and methicillin-resistant strains are common causes of nosocomial- and community-acquired infections. Despite the prevalence of literature characterising staphylococcal pathogenesis in humans, S. aureus is a major cause of infection and disease in a plethora of animal hosts leading to a significant impact on public health and agriculture. Infections in animals are deleterious to animal health, and animals can act as a reservoir for staphylococcal transmission to humans. Host-switching events between humans and animals and amongst animals are frequent and have been accentuated with the domestication and/or commercialisation of specific animal species. Host-switching is typically followed by subsequent adaptation through acquisition and/or loss of mobile genetic elements such as phages, pathogenicity islands and plasmids as well as further host-specific mutations allowing it to expand into new host populations. In this chapter, we will be giving an overview of S. aureus in animals, how this bacterial species was, and is, being transferred to new host species and the key elements thought to be involved in its adaptation to new ecological host niches. We will also highlight animal hosts as a reservoir for the development and transfer of antimicrobial resistance determinants.
Andreas F. Haag, J. Ross Fitzgerald, and José R. Penadés
ASM Press
Tarcisio Brignoli, Andrea G. O. Manetti, Roberto Rosini, Andreas F. Haag, Vincenzo Scarlato, Fabio Bagnoli, and Isabel Delany
Frontiers Media SA
Staphylococcus aureus is a major human pathogen, and a leading cause of soft tissue and blood stream infections. One of the causes of its success as a pathogen is the peculiar array of immune evasion factors through which the bacterium avoids host defenses, where the staphylococcal protein A (SpA) plays a major role thanks to its IgG binding activities. Moreover, SpA has recently been proposed as a promising vaccine antigen. In this study, we evaluated the expression of SpA in a collection of staphylococcal strains, about 7% of which did not express SpA (SpA- strains), despite the presence of the gene. By a comparative genomic analysis, we identified that a mutation in the spa 5′ UTR sequence affecting the RBS is responsible for the loss of SpA in a subset of SpA- strains. Using a high-throughput qRT-PCR approach on a selected panel of virulence-related genes, we identified that the SpA- phenotype is associated with lower spa transcript levels and increased expression and production of capsule as well as other changes in the transcription of several key virulence factors. Our data suggest that the SpA- phenotype has occurred in geographically distinct strains through different molecular mechanisms including both mutation, leading likely to translation alterations, and transcriptional deregulation. Furthermore, we provide evidence that SpA- strains are highly susceptible to phagocytic uptake mediated by anti-capsule antibodies. These data suggest that S. aureus may alter its virulence factor expression pattern as an adaptation to the host or environment. Vaccination strategies targeting both SpA and capsule could therefore result in broader coverage against staphylococcal isolates than SpA alone.
Maan M. Neamah, Ignacio Mir-Sanchis, María López-Sanz, Sonia Acosta, Ignacio Baquedano, Andreas F. Haag, Alberto Marina, Silvia Ayora, and José R. Penadés
Oxford University Press (OUP)
Abstract DNA-single strand annealing proteins (SSAPs) are recombinases frequently encoded in the genome of many bacteriophages. As SSAPs can promote homologous recombination among DNA substrates with an important degree of divergence, these enzymes are involved both in DNA repair and in the generation of phage mosaicisms. Here, analysing Sak and Sak4 as representatives of two different families of SSAPs present in phages infecting the clinically relevant bacterium Staphylococcus aureus, we demonstrate for the first time that these enzymes are absolutely required for phage reproduction. Deletion of the genes encoding these enzymes significantly reduced phage replication and the generation of infectious particles. Complementation studies revealed that these enzymes are required both in the donor (after prophage induction) and in the recipient strain (for infection). Moreover, our results indicated that to perform their function SSAPs require the activity of their cognate single strand binding (Ssb) proteins. Mutational studies demonstrated that the Ssb proteins are also required for phage replication, both in the donor and recipient strain. In summary, our results expand the functions attributed to the Sak and Sak4 proteins, and demonstrate that both SSAPs and Ssb proteins are essential for the life cycle of temperate staphylococcal phages.
Andreas F. Haag and Fabio Bagnoli
Springer International Publishing
Kamila K. Myka, David J. Allcock, Emiley A. Eloe-Fadrosh, Theodora Tryfona, Andreas F. Haag, Federico M. Lauro, Douglas H. Bartlett, and Gail P. Ferguson
Springer International Publishing
Marta Bacconi, Andreas F. Haag, Emiliano Chiarot, Paolo Donato, Fabio Bagnoli, Isabel Delany, and Giuliano Bensi
American Society for Microbiology
ABSTRACT Staphylococcus aureus is an opportunistic human pathogen and a major cause of invasive infections such as bacteremia, endocarditis, pneumonia, and wound infections. FhuD2 is a staphylococcal lipoprotein involved in the uptake of iron-hydroxymate and is under the control of the iron uptake regulator Fur. This protein is part of an investigational multicomponent vaccine formulation that has shown protective efficacy in several murine models of infection. Even though fhuD2 expression has been shown to be upregulated in murine kidneys infected with S. aureus , it is not known whether the bacterium undergoes increased iron deprivation during prolonged infection. Furthermore, different S. aureus infection niches might provide different environments and levels of iron availability, resulting in different fhuD2 expression patterns among organs of the same host. To address these questions, we characterized the in vitro expression of the fhuD2 gene and confirmed Fur-dependent regulation of its expression. We further investigated its expression in mice infected with a bioluminescent reporter strain of S. aureus expressing the luciferase operon under the control of the fhuD2 promoter. The emission of bioluminescence in different organs was followed over a 7-day time course, and quantitative real-time PCR analysis of the RNA transcribed from the endogenous fhuD2 gene was performed. Using this approach, we were able to show that fhuD2 expression was induced during infection in all organs analyzed and that differences in expression were observed at different time points and in different infected organs. Our data suggest that S. aureus undergoes increased iron deprivation during the progression of infection in diverse host organs and accordingly induces dedicated iron acquisition mechanisms. Since FhuD2 plays a central role in providing the pathogen with the required iron, further knowledge of the patterns of fhuD2 expression in vivo during infection will be instrumental in better defining the role of this antigen in S. aureus pathogenesis and as a vaccine antigen.
Luigi Scietti, Katia Sampieri, Irene Pinzuti, Erika Bartolini, Barbara Benucci, Alessia Liguori, Andreas F. Haag, Paola Lo Surdo, Werner Pansegrau, Vincenzo Nardi-Dei,et al.
Springer Science and Business Media LLC
AbstractDuring bacterial pathogenesis extensive contacts between the human and the bacterial extracellular proteomes take place. The identification of novel host-pathogen interactions by standard methods using a case-by-case approach is laborious and time consuming. To overcome this limitation, we took advantage of large libraries of human and bacterial recombinant proteins. We applied a large-scale protein microarray-based screening on two important human pathogens using two different approaches: (I) 75 human extracellular proteins were tested on 159 spotted Staphylococcus aureus recombinant proteins and (II) Neisseria meningitidis adhesin (NadA), an important vaccine component against serogroup B meningococcus, was screened against ≈2300 spotted human recombinant proteins. The approach presented here allowed the identification of the interaction between the S. aureus immune evasion protein FLIPr (formyl-peptide receptor like-1 inhibitory protein) and the human complement component C1q, key players of the offense-defense fighting; and of the interaction between meningococcal NadA and human LOX-1 (low-density oxidized lipoprotein receptor), an endothelial receptor. The novel interactions between bacterial and human extracellular proteins here presented might provide a better understanding of the molecular events underlying S. aureus and N. meningitidis pathogenesis.
Alessia Liguori, Enrico Malito, Paola Lo Surdo, Luca Fagnocchi, Francesca Cantini, Andreas F. Haag, Sébastien Brier, Mariagrazia Pizza, Isabel Delany, and Matthew J. Bottomley
Public Library of Science (PLoS)
Neisseria adhesin A (NadA) is present on the meningococcal surface and contributes to adhesion to and invasion of human cells. NadA is also one of three recombinant antigens in the recently-approved Bexsero vaccine, which protects against serogroup B meningococcus. The amount of NadA on the bacterial surface is of direct relevance in the constant battle of host-pathogen interactions: it influences the ability of the pathogen to engage human cell surface-exposed receptors and, conversely, the bacterial susceptibility to the antibody-mediated immune response. It is therefore important to understand the mechanisms which regulate nadA expression levels, which are predominantly controlled by the transcriptional regulator NadR (Neisseria adhesin A Regulator) both in vitro and in vivo. NadR binds the nadA promoter and represses gene transcription. In the presence of 4-hydroxyphenylacetate (4-HPA), a catabolite present in human saliva both under physiological conditions and during bacterial infection, the binding of NadR to the nadA promoter is attenuated and nadA expression is induced. NadR also mediates ligand-dependent regulation of many other meningococcal genes, for example the highly-conserved multiple adhesin family (maf) genes, which encode proteins emerging with important roles in host-pathogen interactions, immune evasion and niche adaptation. To gain insights into the regulation of NadR mediated by 4-HPA, we combined structural, biochemical, and mutagenesis studies. In particular, two new crystal structures of ligand-free and ligand-bound NadR revealed (i) the molecular basis of ‘conformational selection’ by which a single molecule of 4-HPA binds and stabilizes dimeric NadR in a conformation unsuitable for DNA-binding, (ii) molecular explanations for the binding specificities of different hydroxyphenylacetate ligands, including 3Cl,4-HPA which is produced during inflammation, (iii) the presence of a leucine residue essential for dimerization and conserved in many MarR family proteins, and (iv) four residues (His7, Ser9, Asn11 and Phe25), which are involved in binding 4-HPA, and were confirmed in vitro to have key roles in the regulatory mechanism in bacteria. Overall, this study deepens our molecular understanding of the sophisticated regulatory mechanisms of the expression of nadA and other genes governed by NadR, dependent on interactions with niche-specific signal molecules that may play important roles during meningococcal pathogenesis.
Marta Bacconi, Andreas F. Haag, Antonina Torre, Andrea Castagnetti, Emiliano Chiarot, Isabel Delany, and Giuliano Bensi
Springer Science and Business Media LLC
Andreas F. Haag, Markus F. F. Arnold, Kamila K. Myka, Bernhard Kerscher, Sergio Dall'Angelo, Matteo Zanda, Peter Mergaert, and Gail P. Ferguson
Oxford University Press (OUP)
Rhizobial soil bacteria can form a symbiosis with legumes in which the bacteria fix atmospheric nitrogen into ammonia that can be utilized by the host. The plant, in turn, supplies the rhizobia with a carbon source. After infecting the host cell, the bacteria differentiate into a distinct bacteroid form, which is able to fix nitrogen. The bacterial BacA protein is essential for bacteroid differentiation in legumes producing nodule-specific cysteine-rich peptides (NCRs), which induce the terminal differentiation of the bacteria into bacteroids. NCRs are antimicrobial peptides similar to mammalian defensins, which are important for the eukaryotic response to invading pathogens. The BacA protein is essential for rhizobia to survive the NCR peptide challenge. Similarities in the lifestyle of intracellular pathogenic bacteria suggest that host factors might also be important for inducing chronic infections associated with Brucella abortus and Mycobacterium tuberculosis. Moreover, rhizobial lipopolysaccharide is modified with an unusual fatty acid, which plays an important role in protecting the bacteria from environmental stresses. Mutants defective in the biosynthesis of this fatty acid display bacteroid development defects within the nodule. In this review, we will focus on these key components, which affect rhizobial bacteroid development and survival.
M. F. F. Arnold, A. F. Haag, S. Capewell, H. I. Boshoff, E. K. James, R. McDonald, I. Mair, A. M. Mitchell, B. Kerscher, T. J. Mitchell,et al.
American Society for Microbiology
ABSTRACT The Sinorhizobium meliloti BacA ABC transporter protein plays an important role in its nodulating symbiosis with the legume alfalfa ( Medicago sativa ). The Mycobacterium tuberculosis BacA homolog was found to be important for the maintenance of chronic murine infections, yet its in vivo function is unknown. In the legume plant as well as in the mammalian host, bacteria encounter host antimicrobial peptides (AMPs). We found that the M. tuberculosis BacA protein was able to partially complement the symbiotic defect of an S. meliloti BacA-deficient mutant on alfalfa plants and to protect this mutant in vitro from the antimicrobial activity of a synthetic legume peptide, NCR247, and a recombinant human β-defensin 2 (HBD2). This finding was also confirmed using an M. tuberculosis insertion mutant. Furthermore, M. tuberculosis BacA-mediated protection of the legume symbiont S. meliloti against legume defensins as well as HBD2 is dependent on its attached ATPase domain. In addition, we show that M. tuberculosis BacA mediates peptide uptake of the truncated bovine AMP, Bac7 1-16 . This process required a functional ATPase domain. We therefore suggest that M. tuberculosis BacA is important for the transport of peptides across the cytoplasmic membrane and is part of a complete ABC transporter. Hence, BacA-mediated protection against host AMPs might be important for the maintenance of latent infections.