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PubMed2002

The benPK operon, proposed to play a role in transport, is part of a regulon for benzoate catabolism in Acinetobacter sp. strain ADP1.

BenM and CatM are distinct, but similar, LysR-type transcriptional regulators of the soil bacterium Acinetobacter sp. strain ADP1. Together, the two regulators control the expression of at least 14 genes involved in the degradation of aromatic compounds via the catechol branch of the beta-ketoadipate pathway. In these studies, BenM and CatM were each purified to homogeneity to test the possibility that they regulate the expression of two additional genes, benP and benK, that are adjacent to benM on the chromosome. Each regulator bound to a DNA fragment containing the benP promoter region. Additional transcriptional studies suggested that benP and benK are co-transcribed as an operon, and a site of transcription initiation was identified. Alignment of this initiation site with those of several CatM- and BenM-regulated genes revealed common regulatory motifs. Mutants lacking both CatM and BenM failed to activate benP transcription. The ability of each protein to regulate gene expression was inferred from strains lacking either CatM or BenM that were still capable of increasing benP expression in response to cis,cis-muconate. This compound has previously been shown to induce all enzymes of the catechol branch of the beta-ketoadipate pathway through a complex transcriptional circuit involving CatM and BenM. Thus, the regulated expression of the benPK operon in concert with other genes of the regulon is consistent with the model that BenP, a putative outer-membrane porin, and BenK, an inner-membrane permease, transport aromatic compounds in strain ADP1.

Acinetobacter↗
PubMed1975

Regulation of growth of Acinetobacter calcoaceticus NCIB8250 on L-mandelate in batch culture.

Batch culture of Acinetobacter calcoaceticus in L-mandelate- or phenylglyoxylate-salts medium showed an unusual non-exponential pattern unless the inoculum had been grown on benzyl alcohol. There were transient accumulations of benzaldehyde and benzyl alcohol caused by the limitation of L-mandelate oxidation by low activities of benzaldehyde dehydrogenase and the diversion of reducing power to the formation of benzyl alcohol. In vivo enzymic activities were estimated from patterns of substrate utilization in batch cultures containing pairs of substrates. When bacteria previously grown in L-mandelate-salts medium were inoculated into media containing L-mandelate and a second carbon source, metabolism of L-mandelate was arithmetical in the presence of benzoate, catechol or succinate, but accelerated on exhaustion of the second substrate. This indicated repression of the enzymes involved in L-mandelate oxidation. Inoculation of bacteria grown in benzoate-salts medium into medium containing L-mandelate and benzoate gave diauxie with initial utilization of benzoate. Similar experiments showed that benzoate oxidation was not repressed by catechol and only partially repressed by succinate. Measurement of L-mandelate dehydrogenase, phenylglyoxylate carboxy-lyase and benzaldehyde dehydrogenase I in bacterial extracts showed no evidence for feedback inhibition by intermediates of the pathway. The rates of L-mandelate and benzoate utilization by bacterial suspensions were inhibited by succinate and catechol but not by other intermediates of the pathway.

Acinetobacter↗
PubMed1975

The induction of mutants of Acinetobacter calcoaceticus NCIB8250 and their selection by vancomycin.

The mutagenic and lethal effects of N-methyl-N'-nitro-N-nitrosoguanidine (NTG), ethyl methanesulphonate (EMS), ultraviolet light irradiation and near-ultraviolet light irradiation with 8-methoxypsoralen on the bacterium Acinetobacter calcoaceticus NCIB8250 were examined. The production of auxotrophic mutants was used as a measure of mutagenic efficiency. Under appropriate conditions all four agents were mutagenic. EMS and NTG although more effective than irradiation, did not cause such a high frequency of mutation as has been observed with other bacteria. A combination of vancomycin and penicillin V gave enrichment of non-metabolizing bacteria and optimum conditions were found for the use of these compounds in a selection technique.

Acinetobacter↗
PubMed1976

RP4-mediated conjugation in Acinetobacter calcoaceticus.

The P class R factor RP4 was transferred from Escherichia coli K12 to Acinetobacter calcoaceticus. RP4 conferred similar levels of antibiotic resistance in A. calcoaceticus to those in the E. coli K12 donor. Only slight instability of RP4 in A. calcoaceticus was detected. Transfer of RP4 between strains of A. calcoaceticus was by conjugation and was accompanied by transfer of chromosomal genes. Possible polarity of marker transfer was observed and linkage between a number of chromosomal markers was demonstrated.

Acinetobacter↗
PubMed1976

Regulation of growth of Acinetobacter calcoaceticus NCIB8250 on benzyl alcohol in batch culture.

Formation of benzoate and catechol during oxidation of benzyl alcohol by washed suspensions of Acinetobacter calcoaceticus NCIB8250 confirmed earlier results indicating that this organism metabolizes benzyl alcohol via benzaldehyde, benzoate, and the 3-oxoadipate pathway. There was no evidence for feedback inhibition of benzyl alcohol dehydrogenase or benzaldehyde dehydrogenase II. Examination of growth curves and patterns of substrate utilization, as well as measurement of enzyme activities, showed that benzyl alcohol dehydrogenase and benzaldehyde dehydrogenase II are repressed when A. calcoaceticus utilizes L-mandelate or phenylglyoxylate. Growth of bacteria on L-mandelate prior to their inoculation into benzyl alcohol/salts medium leads to an exceptionally long lag period before benzyl alcohol is used at the maximum rate. Benzyl alcohol metabolism is also suppressed during growth on benzoate.

Acinetobacter↗
PubMed1995

Phenotypic characterisation of Acinetobacter strains of 13 DNA-DNA hybridisation groups by means of the biolog system.

A collection of 129 Acinetobacter strains belonging to DNA groups (genomic species) 1-14 (1-7 and 10-12 sensu Bouvet and Grimont; 8 and 13-14 sensu Tjernberg and Ursing) were investigated for their ability to oxidise 95 carbon sources in the Biolog system. The strain groupings obtained by cluster analysis with the Biolog software were compared with the results of DNA-DNA hybridisation studies. Strains of DNA groups 1 (A. calcoaceticus), 2 (A. baumannii), 3 and 13 were linked in one cluster, as were DNA groups 4 (A. haemolyticus) and 6, DNA groups 10 and 11, and DNA groups 8 (A. lwoffii) and 12 (A. radioresistens). Strains of DNA group 5 (A. junii) were grouped in a single cluster with one strain of DNA group 4. Strains of DNA groups 7 (A. johnsonii) and 14 formed separate clusters. With the exception of the linkage of DNA groups 8 and 12, these results correlated with classification of reference strains of the DNA groups by DNA-DNA hybridisation, but six strains of four different DNA groups were not allocated to the clusters of their respective DNA groups. In the case of DNA groups 4, 5, 6, 7, 10, 11 and 14, at least one carbon source oxidation test could be used to differentiate them from the other DNA groups.

Acinetobacter↗
PubMed1975

Observations on the growth and movement of Acinetobacter on semi-solid media.

The growth of 29 strains of Acinetobacter spp. on semi-solid media was studied; 19 showed surface swarming and 14 produced channels ("ditches") in the agar that do not seem to have been described previously. An attempt was made to define the cultural and physical conditions for the demonstration of these phenomena. Possible taxonomic implications are discussed.

Acinetobacter↗
PubMed1994

NADP-dependent alcohol dehydrogenases in bacteria and yeast: purification and partial characterization of the enzymes from Acinetobacter calcoaceticus and Saccharomyces cerevisiae.

An NADP-dependent constitutive alcohol dehydrogenase that can oxidize hexan-1-ol was detected in several Gram-positive and Gram-negative eubacteria and in two yeasts. The enzyme was purified to homogeneity from Acinetobacter calcoaceticus NCIB 8250 and from Saccharomyces cerevisiae D273-10B. The bacterial enzyme appears to be a tetramer of subunit M(r) 40,300 and the yeast enzyme appears to be a monomer of subunit M(r) 43,500. The N-terminal amino acid sequence of the bacterial enzyme has 34% identity with part of the sequence of a fermentative alcohol dehydrogenase from Escherichia coli. The pI value of the bacterial enzyme was 5.7 and the pH optimum was 10.2. Both the bacterial and yeast enzymes were shown to transfer the pro-R hydrogen to/from NADP(H). The substrate specificities of the two enzymes were similar to each other, both oxidizing primary alcohols and some diols, but not secondary alcohols. The maximum velocities of both enzymes were with pentan-1-ol as substrate and there was very low activity with ethanol; the maximum specificity constants were found with primary alcohols containing six to eight carbon atoms. Neither enzyme was significantly inhibited by metal-binding agents but some thiol-blocking compounds inhibited them. It appears that these two alcohol dehydrogenases, on prokaryotic and one eukaryotic, are structurally, kinetically and functionally different from members of the major known groups of alcohol dehydrogenases.

Acinetobacter calcoaceticus↗
PubMed1995

Two genes encoding proteins with similarities to rubredoxin and rubredoxin reductase are required for conversion of dodecane to lauric acid in Acinetobacter calcoaceticus ADP1.

Mutants of Acinetobacter calcoaceticus ADP1 unable to grow on dodecane, but retaining the ability to grow on lauric acid were isolated after ethylmethanesulphonate (EMS) treatment. This growth deficiency was complemented by a clone from a gene library constructed from chromosomal DNA of the wild-type strain. The complementing DNA mapped in a gene encoding a polypeptide with homology to rubredoxins. The deduced putative rubredoxin amino acid sequence is more similar to related proteins from Gram-positive bacteria than to the Pseudomonas oleovorans rubredoxin involved in alkane oxidation. An adjacent gene encodes a protein with similarity to rubredoxin reductase from Pseudomonas oleovorans and related NAD(P)-dependent reductases. Disruption of the rubredoxin-encoding gene by insertion of a KmR/lacZ cassette rendered the resulting strain unable to grow on dodecane or hexadecane. This demonstrates that these genes are necessary for alkane degradation. Transcriptional fusion of lacZ to the rubredoxin-encoding gene led to low level constitutive beta-galactosidase expression, whereas the fusion oriented in the opposite direction was not expressed.

Acinetobacter calcoaceticus↗
PubMed1996

IS1236, a newly discovered member of the IS3 family, exhibits varied patterns of insertion into the Acinetobacter calcoaceticus chromosome.

Analysis of spontaneous mutations in Acinetobacter calcoaceticus revealed a 1237 bp insertion sequence named IS1236 and possessing a nucleotide sequence resembling those of members of the lS3 family. The chromosome of A. calcoaceticus strain ADP1 contains seven copies of IS1236 which appears to insert preferentially into pobR, the transcriptional activator of the structural gene for p-hydroxybenzoate hydroxylase. IS1236 creates tandem 3 bp DNA duplications flanking the sites of its insertion in pobR. Different duplication patterns are found following insertion of IS1236 into pcaH, a structural gene for protocatechuate 3,4-dioxygenase. Therefore the insertion of properties of IS1236 appear to be influenced by its DNA target. Amino acid sequences associated with the apparent transposase function have been conserved in ORFB of IS1236 whereas the presumed DNA-binding helix-turn-helix region of IS1236 ORFA exhibits substantial amino acid sequence divergence from its IS3 counterparts. IS1236 ORFA and ORFB coding sequences overlap considerably, and sequence evidence indicates mechanisms for ORFB expression in IS1236 may resemble those employed by other members of the IS3 family. Portions of the IS1236 terminal repeats exhibit substantial sequence divergence from other members of the IS3 family, but evolution appears to have conserved a mechanism preventing expression of the insertion sequence genes as a consequence of transcriptional readthrough.

Acinetobacter calcoaceticus↗
PubMed1999

The effect of heavy metals and other environmental conditions on the anaerobic phosphate metabolism of Acinetobacter johnsonii.

A strain of Acinetobacter with potential for bioremediation of heavy metal-contaminated waters was isolated from a wastewater-treatment plant operating an enhanced biological phosphate removal process. NMR and extractive methods showed that polyphosphate accumulated aerobically was degraded under anaerobic conditions both in the presence and absence of cadmium or uranium (0.2-0.5 mM). NMR showed that free phosphate was formed at the expense of polyphosphate, and an extractive technique indicated that this reaction could be stimulated by the presence of UO(2)2+ under these conditions. Energy-dispersive X-ray microanalysis demonstrated that only cadmium could enter the cells, and co-localized with intra-cellular granules containing phosphate and other divalent metals. The effects of other environmental parameters on the anaerobic phosphate metabolism were also investigated. Between pH 5.5 and 8.0, phosphate release increased with increasing pH. Between 4 degrees C and 37 degrees C, phosphate release increased with increasing temperature. The presence of nitrate at concentrations of 10 mM and above inhibited anoxic phosphate release, but supplying tungstate in the growth medium prior to anoxic incubation reduced the production of active nitrate reductase and alleviated this effect.

Acinetobacter↗
PubMed2004

Diversity of aminoglycoside-resistance genes and their association with class 1 integrons among strains of pan-European Acinetobacter baumannii clones.

The purpose of the present study was to investigate the diversity of the genes encoding aminoglycoside-modifying enzymes and their association with class 1 integrons in three pan-European clones of Acinetobacter baumannii. The study collection included 106 multidrug-resistant strains previously allocated to clone I (n = 56), clone II (n = 36) and clone III (n = 6) and a heterogeneous group of other strains (n = 8), using AFLP fingerprinting and ribotyping. The strains were from hospitals of the Czech Republic (n = 70; collected 1991-2001) and 12 other European countries (n = 36; 1982-1998). Using PCR, at least one of the following aminoglycoside-resistance genes was detected in 101 (95 %) strains: aphA1 (n = 76), aacC1 (n = 68), aadA1 (n = 68), aphA6 (n = 55), aadB (n = 31), aacC2 (n = 7) and aacA4 (n = 3). A combination of two to five different resistance genes was observed in 89 strains (84 %), with a total of 12 different combinations. PCR mapping revealed that aacC1, aadA1 and aacA4 were each associated with a class 1 integron, as was the case with aadB for six strains of clone III. Six different class 1 integron variable regions were detected in 78 strains (74 %), with two predominant regions (2.5 and 3.0 kb) in two sets of 34 strains each. The 3.0 kb region contained five gene cassettes (aacC1, orfX, orfX, orfX', aadA1) and differed from the 2.5 bp region only by one additional orfX cassette. These two integron regions were confined to clones I and II and were found in strains isolated in seven countries between 1982 and 2001. The clone III strains were homogeneous both in resistance genes and in integron variable regions, whereas clones I and II showed a remarkable intraclonal diversity of these properties, with no clear-cut difference between the two clones. Yet, within the Czech clone I and II strains, the diversity of resistance genes and integron structures was limited as compared to those from other countries. The occurrence of identical resistance genes, gene combinations and class 1 integrons associated with these genes in clonally distinct strains indicates that horizontal gene transfer plays a major role in the dissemination of aminoglycoside resistance in A. baumannii.

Acinetobacter baumannii↗
PubMed2006

The diversity of definitions of multidrug-resistant (MDR) and pandrug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa.

Different definitions of the terms multidrug-resistant (MDR) and pandrug-resistant (PDR) Acinetobacter baumannii and Pseudomonas aeruginosa have been used in the biomedical literature. The authors searched for relevant studies indexed in the PubMed database (01/2000-09/2005) to systematically examine the various definitions of MDR and PDR for these bacteria. Initially 107 retrieved relevant studies were reviewed. Ninety-two studies were further analysed, 50 of which focused on A. baumannii and 42 on P. aeruginosa. A considerable diversity of definitions of the terms MDR and PDR A. baumannii and P. aeruginosa was found. Of note, the term PDR was inappropriately used in all five studies that used it. The review reveals that various definitions have been used for the terms MDR and PDR A. baumannii and P. aeruginosa, a fact that causes confusion to researchers and clinicians. The authors believe that at least a widely accepted definition for PDR A. baumannii and P. aeruginosa should be uniformly used worldwide.

Acinetobacter baumannii↗
PubMed2026

Phenylacetic acid mediates Acinetobacter baumannii entry into a viable but non-culturable state.

Desiccation tolerance is central to the pathogenic success of the opportunistic pathogen Acinetobacter baumannii, allowing its survival on hospital surfaces in the absence of water and nutrients for months at a time, compromising surface decontamination and aiding cross-contamination between staff and patients. Despite the importance of desiccation tolerance, the regulation underpinning this behaviour remains largely elusive. In this work, transcriptomic analyses of desiccated cells revealed phenylacetic acid (PAA) catabolism as an essential mediator of desiccation tolerance. We subsequently demonstrate that deletion of the paa operon abolished the clonogenicity of desiccated cells. Strikingly, these A. baumannii cells remained viable by entering the viable but non-culturable (VBNC) state, a means to survive extreme stressors like antibiotic exposure. Furthermore, we uncover that PAA catabolism is necessary to mediate PAA-driven biofilm regulation. These findings highlight PAA catabolism as a modulator of biofilm formation and a key pathway for entry into the VBNC state in response to desiccation. This reveals PAA catabolism as a target for novel infection prevention strategies.

Phenylacetates↗
PubMed2003

Genetic organization of an Acinetobacter baumannii chromosomal region harbouring genes related to siderophore biosynthesis and transport.

The Acinetobacter baumannii 8399 clinical isolate secretes dihydroxybenzoic acid (DHBA) and a high-affinity catechol siderophore, which is different from other bacterial iron chelators already characterized. Complementation assays with enterobactin-deficient Escherichia coli strains led to the isolation of a cosmid clone containing A. baumannii 8399 genes required for the biosynthesis and activation of DHBA. Accordingly, the cloned fragment harbours a dhbACEB polycistronic operon encoding predicted proteins highly similar to several bacterial proteins required for DHBA biosynthesis from chorismic acid. Genes encoding deduced proteins related to the E. coli Fes and the Bacillus subtilis DhbF proteins, and a putative Yersinia pestis phosphopantetheinyl transferase, all of them involved in the assembly and utilization of catechol siderophores in other bacteria, were found next to the dhbACEB locus. This A. baumannii 8399 gene cluster also contained the om73, p45 and p114 predicted genes encoding proteins potentially involved in transport of ferric siderophore complexes. The deduced products of the p114 and p45 genes are putative membrane proteins that belong to the RND and MFS efflux pump proteins, respectively. Interestingly, P45 is highly related to the E. coli P43 (EntS) protein that participates in the secretion of enterobactin. Although P114 is similar to other bacterial efflux pump proteins involved in antibiotic resistance, its genetic arrangement within this A. baumannii 8399 locus is different from that described in other bacteria. The product of om73 is a Fur- and iron-regulated surface-exposed outer-membrane protein. These characteristics together with the presence of a predicted TonB box and its high similarity to other siderophore receptors indicate that OM73 plays such a role in A. baumannii 8399. The 184 nt om73-p114 intergenic region contains promoter elements that could drive the expression of these divergently transcribed genes, all of which are in close proximity to almost perfect Fur boxes. This arrangement explains the iron- and Fur-regulated expression of om73, and provides strong evidence for a similar regulation for the expression of p114.

Acinetobacter baumannii↗
PubMed2003

Attachment to and biofilm formation on abiotic surfaces by Acinetobacter baumannii: involvement of a novel chaperone-usher pili assembly system.

Acinetobacter baumannii causes severe infections in compromised patients, survives on abiotic surfaces in hospital environments and colonizes different medical devices. In this study the analysis of the processes involved in surface attachment and biofilm formation by the prototype strain 19606 was initiated. This strain attaches to and forms biofilm structures on plastic and glass surfaces, particularly at the liquid-air interface of cultures incubated stagnantly. The cell aggregates, which contain cell stacks separated by water channels, formed under different culture conditions and were significantly enhanced under iron limitation. Electron and fluorescence microscopy showed that pili and exopolysaccharides are part of the cell aggregates formed by this strain. Electron microscopy of two insertion derivatives deficient in attachment and biofilm formation revealed the disappearance of pili-like structures and DNA sequencing analysis showed that the transposon insertions interrupted genes with the highest similarity to hypothetical genes found in Pseudomonas aeruginosa, Pseudomonas putida and Vibrio parahaemolyticus. Although the products of these genes, which have been named csuC and csuE, have no known functions, they are located within a polycistronic operon that includes four other genes, two of which encode proteins related to chaperones and ushers involved in pili assembly in other bacteria. Introduction of a copy of the csuE parental gene restored the adherence phenotype and the presence of pili on the cell surface of the csuE mutant, but not that of the csuC derivative. These results demonstrate that the expression of a chaperone-usher secretion system, some of whose components appear to be acquired from unrelated sources, is required for pili formation and the concomitant attachment to plastic surfaces and the ensuing formation of biofilms by A. baumannii cells.

Acinetobacter baumannii↗
PubMed2004

Partial purification and characterization of a non-cyanobacterial cyanophycin synthetase from Acinetobacter calcoaceticus strain ADP1 with regard to substrate specificity, substrate affinity and binding to cyanophycin.

This study reports, for the first time, purification and biochemical characterization of a cyanophycin synthetase from a non-cyanobacterial strain. Cyanophycin synthetase of Acinetobacter calcoaceticus strain ADP1 was purified 69-fold from recombinant Escherichia coli by two chromatographic steps and one novel affinity step utilizing the Mg(2+)-dependent binding of the enzyme to cyanophycin. Unlike cyanobacterial cyanophycin synthetases characterized so far, the purified enzyme from A. calcoaceticus strain ADP1 did not accept lysine as an alternative substrate to arginine. The apparent K(m)-values for arginine (47 microM) and aspartic acid (240 microM) were similar to those of known cyanophycin synthetases from cyanobacteria, but this enzyme had a slightly higher affinity for aspartic acid. In addition, the two different ATP-binding sites of the enzyme were characterized independently of each other with respect to K(m) values for ATP. The ATP-binding site responsible for the addition of arginine was found to have a much higher affinity for ATP (38 microM) than that responsible for the addition of aspartate (210 mM). Furthermore, the binding of the enzyme to the two possible forms of cyanophycin granule polypeptide (CGP), CGP-Asp and CGP-Arg, was studied. While both forms bound around 30-40 % of the enzyme activity present under the assay conditions, binding was Mg(2+)-dependent in the case of CGP-Asp. Two-dimensional gel electrophoresis revealed that both forms of cyanophycin were equally abundant in cyanophycin-accumulating cells of A. calcoaceticus ADP1.

Acinetobacter calcoaceticus↗
PubMed2004

Identification and transcriptional organization of a gene cluster involved in biosynthesis and transport of acinetobactin, a siderophore produced by Acinetobacter baumannii ATCC 19606T.

In order to assimilate iron, Acinetobacter baumannii ATCC 19606(T) produces a siderophore named acinetobactin (Ab) that is composed of equimolar quantities of 2,3-dihydroxybenzoic acid (DHBA), L-threonine and N-hydroxyhistamine. Application of the Fur titration assay system to A. baumannii genomic libraries, followed by further cloning of the regions surrounding the candidate genes, led to the identification of the Ab cluster, which harbours the genetic determinants necessary for the biosynthesis and transport of the siderophore. However, an entA homologue essential for DHBA biosynthesis was not found in this cluster. Functions of potential biosynthetic genes inferred by homology studies suggested that the precursors, DHBA, l-threonine and N-hydroxyhistamine, are linked in steps resembling those of bacterial non-ribosomal peptide synthesis to form Ab. Genes responsible for the two-step biosynthesis of N-hydroxyhistamine from histidine were also identified in this cluster. Their genetic organization suggests that five genes involved in the transport system of ferric Ab into the cell cytosol form an operon. Construction of disruptants of some selected genes followed by phenotypic analysis supported their predicted biological functions. Interestingly, three additional genes probably involved in the intracellular release of iron from ferric Ab and the secretion of nascent Ab are contained in this cluster. Primer extension and RT-PCR analyses suggested that the Ab cluster, which includes 18 genes, is organized in seven transcriptional units originating from respective Fur-regulated promoter-operator regions.

Acinetobacter baumannii↗