377 research outputs found
Identification of unique cardiolipin and monolysocardiolipin species in Acinetobacter baumannii
No full textAcidic glycerophospholipids play an important role in determining the resistance of Gram-negative bacteria to stress conditions and antibiotics. Acinetobacter baumannii, an opportunistic human pathogen which is responsible for an increasing number of nosocomial infections, exhibits broad antibiotic resistances. Here lipids of A. baumannii have been analyzed by combined MALDI-TOF/MS and TLC analyses; in addition GC-MS analyses of fatty acid methyl esters released by methanolysis of membrane phospholipids have been performed. The main glycerophospholipids are phosphatidylethanolamine, phosphatidylglycerol, acyl-phosphatidylglycerol and cardiolipin together with monolysocardiolipin, a lysophospholipid only rarely detected in bacterial membranes. The major acyl chains in the phospholipids are C16:0 and C18:1, plus minor amounts of short chain fatty acids. The structures of the cardiolipin and monolysocardiolipin have been elucidated by post source decay mass spectrometry analysis. A large variety of cardiolipin and monolysocardiolipin species were found in A. baumannii. Similar lysocardiolipin levels were found in the two clinical strains A. baumannii ATCC19606(T) and AYE whereas in the nonpathogenic strain Acinetobacter baylyi ADP1 lysocardiolipin levels were highly reduced
Identification and characterization of a novel pathway for aldopentose degradation in Acinetobacter baumannii
No full textAbstract The nosocomial pathogen Acinetobacter baumannii is well known for its extraordinary metabolic diversity. Recently, we demonstrated growth on L‐arabinose, but the pathway remained elusive. Transcriptome analyses revealed two upregulated gene clusters that code for isoenzymes catalysing oxidation of a pentonate to α‐ketoglutarate. Molecular, genetic, and biochemical experiments revealed one branch to be specific for L‐arabonate oxidation, and the other for D‐xylonate and D‐ribonate. Both clusters also encode an uptake system and a regulator that acts as activator (L‐arabonate) or repressor (D‐xylonate and D‐ribonate). Genes encoding the initial oxidation of pentose to pentonate were not part of the clusters, but our data are consistent with the hypothesis of a promiscous, pyrroloquinoline quinone (PQQ)‐dependent, periplasmic pentose dehydrogenase, followed by the uptake of the pentonates and their degradation by specific pathways. However, there is a cross‐talk between the two different pathways since the isoenzymes can replace each other. Growth on pentoses was found only in pathogenic Acinetobacter species but not in non‐pathogenic such as Acinetobacter baylyi . However, mutants impaired in growth on pentoses were not affected in traits important for infection, but growth on L‐arabinose was beneficial for long‐term survival and desiccation resistance in A. baumannii ATCC 19606.Deutsche Forschungsgemeinschaft https://doi.org/10.13039/50110000165
HB27
No full textThe mesophile Acinetobacter sp, strain BD413 and the extreme thermophile Thermus thremophilus HB27 display high frequencies of natural transformation. In this study we identified and characterized a novel competence gene in Acinetobacter sp, strain BD413, com;l, whose product displays significant similarities to the competence proteins ComA and ComEC in Neisseria and Bacillus species, Transcription of comA correlated with growth phase-dependent transcriptional regulation of the recently identified pilin-like factors of the transformation machinery. This finding strongly suggests that comA is part of a competence regulon, Examination of the genome sequence of T, thermophilus HB27 led to detection of a comA/comEC-like open reading frame (ORF) which is flanked by an ORF whose product shows significant similarities to the Bacillus subtilis competence protein ComEA. To examine whether these two ORFs, designated comEC and comEA, are implicated in natural transformation of T, thermophilus HB27, both were disrupted by using a thermostable kana-mycin resistance marker, Natural transformation in comEC mutants was reduced 1,000-fold, whereas in comEA mutants the natural transformation phenotype was completely eliminated. These results strongly suggest that both genes, comEC and comEA, are required far natural transformation in T, thermophilus HB27, Several transmembrane cr-helices are predicted based on the amino acid sequences of ComA in Acinetobacter sp, strain BD413 and ComEC in T, thermophilus HB27, which suggests that ComA and ComEC are located in the inner membrane and function in DNA transport through the cytoplasmic membrane
Beate Sigriddaughter’s Story of Sigrid
No full textdeath of childNorth VancouverteachingWorld War II1910’sEurop
The VBNC state: a fundamental survival strategy of Acinetobacter baumannii
No full textABSTRACT The viable but non-culturable (VBNC) state is a persistence strategy adopted by bacteria to withstand long-lasting periods of unfavorable conditions. VBNC cells evade classical detection methods and are therefore easily transmitted in the hospital causing relapsing infections. The opportunistic human pathogen Acinetobacter baumannii has become a major threat in health care institutions and the food industry due to multiple antibiotic resistances and its ability to quickly adapt to very different ecological niches. Here, we report an additional, novel survival strategy of A. baumannii. Upon prolonged incubation in high-salt media, cells became unculturable. However, LIVE/DEAD staining followed by flow cytometry, respiratory activity assays, and resuscitation experiments revealed that these cells were viable but non-culturable. VBNC cells underwent large morphological changes. Entry into the VBNC state was also induced by pH and temperature stress, as well as by desiccation and anaerobiosis. The VBNC state was found in several strains of A. baumannii. Genome-wide expression profiling revealed a plethora of genes differentially regulated upon entry into the VBNC state. In summary, this study presents unequivocal evidence for a dormancy state in A. baumannii that has important consequences for detection of this pathogen and recurrent outbreaks. IMPORTANCE Currently, the viable but non-culturable (VBNC) state is an underappreciated niche for pathogenic bacteria which provides a continuous source for recurrent infections and transmission. We propose the VBNC state to be a global persistence mechanism used by various A. baumannii strains to cope with many stresses it is confronted with in the clinical environment and in the host. This requires a novel strategy to detect viable cells of this pathogen that is not only based on plating assays
Noncanonical cell-to-cell DNA transfer in Thermus spp. Is insensitive to argonaute-mediated interference
No full textHorizontal gene transfer drives the rapid evolution of bacterial populations. Classical processes that promote the lateral flow of genetic information are conserved throughout the prokaryotic world. However, some species have nonconserved transfer mechanisms that are not well known. This is the case for the ancient extreme thermophile Thermus thermophilus. In this work, we show that T. thermophilus strains are capable of exchanging large DNA fragments by a novel mechanism that requires cell-tocell contacts and employs components of the natural transformation machinery. This process facilitates the bidirectional transfer of virtually any DNA locus but favors by 10-fold loci found in the megaplasmid over those in the chromosome. In contrast to naked DNA acquisition by transformation, the system does not activate the recently described DNA-DNA interference mechanism mediated by the prokaryotic Argonaute protein, thus allowing the organism to distinguish between DNA transferred from a mate and exogenous DNA acquired from unknown hosts. This Argonaute-mediated discrimination may be tentatively viewed as a strategy for safe sharing of potentially >useful> traits by the components of a given population of Thermus spp. without increasing the genome sizes of its individuals.This work has been supported by grant BIO2013-44963-R from the Spanish Ministry of Economy and Competence and FP7-PEOPLE-2012-IAPP grant 324439 from the European Union to J. Berenguer and by grant AV9/6-1 from the Deutsche Forschungsgemeinschaft to B. Averhoff. An institutional grant from the Fundación Ramón Areces to CBMSO and financial support to the Spanish National Network for Extremophilic Microorganisms (BIO2011-12879-E) are also acknowledged.Peer Reviewe
An investigation of horizontal transfer of feed introduced DNA to the aerobic microbiota of the gastrointestinal tract of rats
No full textBACKGROUND:
Horizontal gene transfer through natural transformation of members of the microbiota of the lower gastrointestinal tract (GIT) of mammals has not yet been described. Insufficient DNA sequence similarity for homologous recombination to occur has been identified as the major barrier to interspecies transfer of chromosomal DNA in bacteria. In this study we determined if regions of high DNA similarity between the genomes of the indigenous bacteria in the GIT of rats and feed introduced DNA could lead to homologous recombination and acquisition of antibiotic resistance genes.
RESULTS:
Plasmid DNA with two resistance genes (nptI and aadA) and regions of high DNA similarity to 16S rRNA and 23S rRNA genes present in a broad range of bacterial species present in the GIT, were constructed and added to standard rat feed. Six rats, with a normal microbiota, were fed DNA containing pellets daily over four days before sampling of the microbiota from the different GI compartments (stomach, small intestine, cecum and colon). In addition, two rats were included as negative controls. Antibiotic resistant colonies growing on selective media were screened for recombination with feed introduced DNA by PCR targeting unique sites in the putatively recombined regions. No transformants were identified among 441 tested isolates.
CONCLUSIONS:
The analyses showed that extensive ingestion of DNA (100 μg plasmid) per day did not lead to increased proportions of kanamycin resistant bacteria, nor did it produce detectable transformants among the aerobic microbiota examined for 6 rats (detection limit < 1 transformant per 1,1 × 108 cultured bacteria). The key methodological challenges to HGT detection in animal feedings trials are identified and discussed. This study is consistent with other studies suggesting natural transformation is not detectable in the GIT of mammals
Shuffling genes around in hot environments: the unique DNA transporter ofThermus thermophilus
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