Molecular and genetic analysis of iron uptake proteins in the brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius

Characterization of the IgA1 protease from the Brazilian purpuric fever strain F3031 of Haemophilus influenzae biogroup aegyptius

Brazilian purpuric fever is a severe vascular disease caused by an invasive clone of Haemophilus influenzae biogroup aegyptius, which normally causes self-limiting eye infections. A previous genome subtraction procedure resulted in the isolation of a DNA fragment, which encodes a putative IgA1 protease, specific to the F3031 Brazilian purpuric fever type strain. Cloning and sequencing of the entire F3031 iga1 gene showed that the subtracted DNA fragment encompasses the iga1 region encoding the active site and the cleavage specificity determinant of the protein, which are different from the cognate regions of the proteases produced by other H. influenzae strains. Western and IgA cleavage assays together with clustering analysis showed that the F3031 IgA1 protease is most similar to the type 2 proteases produced by H. influenzae type c and e strains. Analysis of the promoter region of the F3031 iga1 gene revealed the presence of Fur binding sites. However, real-time PCR analysis and transcriptional fusion assays showed that the expression of iga1 is not regulated by iron or hemin under the conditions tested.

Analysis of pVU3695, a plasmid encoding glutathione-dependent formaldehyde dehydrogenase activity and formaldehyde resistance in the Escherichia coli VU3695 clinical strain

The formaldehyde resistance of Escherichia coli VU3695 is due to the expression of glutathione-dependent formaldehyde dehydrogenase (GSH-FDH) activity, which is encoded by the adhC gene located on the plasmid pVU3695. Conjugation of this plasmid to an unrelated PolA deficient strain of E. coli indicated that it encodes its own replication initiation protein and does not confer resistance to several other antimicrobial agents tested in this work. In addition, pVU3695 has homology with replicons that belong to the IncL/M plasmid incompatibility group, which are widely distributed among the Enterobacteriaceae. Curing of pVU3695 abolished the expression of formaldehyde resistance and the presence of a 46-kDa periplasmic protein immunologically related to GSH-FDH. However, the curing of pVU3695 reduced drastically but did not abolish the expression of a protein with similar electrophoretic motility, which was associated with the expression of GSH-FDH activity still present in the cytoplasm of the plasmidless derivative. The data demonstrate that E. coli VU3695 contains a chromosomal and a plasmid copy of adhC actively expressed, with the latter being involved in resistance to exogenous formaldehyde.

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.

Genomic analysis of the F3031 Brazilian purpuric fever clone of Haemophilus influenzae biogroup aegyptius by PCR-based subtractive hybridization

PCR-based subtractive genome hybridization produced clones harboring inserts present in Brazilian purpuric fever (BPF) prototype strain F3031 but absent in noninvasive Haemophilus influenzae biogroup aegyptius isolate F1947. Some of these inserts have no matches in the GenBank database, while others are similar to genes encoding either known or hypothetical proteins. One insert represents a 2.3-kb locus with similarity to a Thermotoga maritima hypothetical protein, while another is part of a 7.6-kb locus that contains predicted genes encoding hypothetical, phage-related, and carotovoricin Er-like proteins. The presence of DNA related to these loci is variable among BPF isolates and nontypeable H. influenzae strains, while neither of them was detected in strains of types a to f. The data indicate that BPF-causing strain F3031 harbors unique chromosomal regions, most of which appear to be acquired from unrelated microbial sources.

Acinetobacter baumannii has two genes encoding glutathione-dependent formaldehyde dehydrogenase: evidence for differential regulation in response to iron

The adhC1 gene from Acinetobacter baumannii 8399, which encodes a glutathione-dependent formaldehyde dehydrogenase (GSH-FDH), was identified and cloned after mapping the insertion site of Tn3-HoHo1 in a recombinant cosmid isolated from a gene library. Sequence analysis showed that this gene encodes a protein exhibiting significant similarity to alcohol dehydrogenases in bacterial, yeast, plant and animal cells. The expression of the adhC1 gene was confirmed by the detection of GSH-FDH enzyme activity in A. baumannii and Escherichia coli cells that expressed the cloned gene. However, the construction and analysis of an A. baumannii 8399 adhC1::Tn3-HoHo1 isogenic derivative revealed the presence of adhC2, a second copy of the gene encoding GSH-FDH activity. Enzyme assays and immunoblot analysis showed that adhC2 encodes a 46.5 kDa protein that is produced in similar amounts under iron-rich and iron-limited conditions. In contrast, the expression of adhC1, which encodes a 45 kDa protein with GSH-FDH activity, is induced under iron limitation and repressed when the cells are cultured in the presence of free inorganic iron. The differential expression of adhC1 is controlled at the transcriptional level and mediated through the Fur iron-repressor protein, which has potential binding sites within the promoter region of this adhC copy. The expression of both adhC copies is significantly enhanced by the presence of sub-inhibitory concentrations of formaldehyde in the culture media. Examination of different A. baumannii isolates indicates that they can be divided into two groups based on the type of GSH-FDH they produce. One group contains only the constitutively expressed 46.5 kDa protein, whilst the other produces this GSH-FDH type in addition to the iron-regulated isoenzyme. Further analysis showed that the presence and expression of the two adhC genes does not confer resistance to exogenous formaldehyde, nor does it enable it to utilize methylated compounds as a sole carbon source when cultured under iron-rich as well as iron-deficient conditions.