Five-Member Gene Family of Bartonella quintana

Abstract

Bartonella quintana, the agent of trench fever and an etiologic agent of bacillary angiomatosis, has an extraordinarily high hemin requirement for growth compared to other bacterial pathogens. We previously identified the major hemin receptor of the pathogen as a 30-kDa surface protein, termed HbpA. This report describes four additional homologues that share approximately 48% amino acid sequence identity with hbpA. Three of the genes form a paralagous cluster, termed hbpCAB, whereas the other members, hbpD and hbpE, are unlinked. Secondary structure predictions and other evidence suggest that Hbp family members are ␤-barrels located in the outer membrane and contain eight transmembrane domains plus four extracellular loops. Homologs from a variety of gram-negative pathogens were identified, including Bartonella henselae Pap31, Brucella Omp31, Agrobacterium tumefaciens Omp25, and neisserial opacity proteins (Opa). Family members expressed in vitro-synthesized proteins ranging from ca. 26.5 to 35.1 kDa, with the exception of HbpB, an ϳ55.9-kDa protein whose respective gene has been disrupted by a ϳ510 GC-rich element containing variablenumber tandem repeats. Transcription analysis by quantitative reverse transcriptase-PCR (RT-PCR) indicates that all family members are expressed under normal culture conditions, with hbpD and hbpB transcripts being the most abundant and the rarest, respectively. Mutagenesis of hbpA by allelic exchange produced a strain that exhibited an enhanced hemin-binding phenotype relative to the parental strain, and analysis by quantitative RT-PCR showed elevated transcript levels for the other hbp family members, suggesting that compensatory expression occurs.

Predominant Outer Membrane Antigens of Bartonella henselae

“…It is more plausible that these proteins are not immunogenic or are undergoing antigenic variation. Genes encoding multiple HbpA homologs in B. quintana have been identified (28). Therefore, it seems most likely that B. henselae also harbors multiple hbp genes, which provide a genetic reservoir for HbpA variability.…”

Characterization of the Natural Population of Bartonella henselae by Multilocus Sequence Typing

“…is not yet clear, but such diversity in a gene that may encode an essential hemin-binding protein (28) should prove useful in an evolved B. henselae MLST scheme. Although the uniqueness of the Berlin-2 isolate (ST7) illustrates that there are alleles of several loci that may be present in Europe and elsewhere that were not encountered in the smaller Australasian gene pool, previous studies have suggested that the number of genetic subgroups within the species is limited (10,13,(36)(37)(38).…”

The louse-borne human pathogen Bartonella quintana is a genomic derivative of the zoonotic agent Bartonella henselae

“…Consistently, B. quintana and B. henselae have the highest reported hemin requirement for bacterial growth in vitro (39), and no genes for hemin biosynthesis were identified in either genome. A hemin-binding protein was characterized in B. quintana, and four additional members of this gene family were identified, all of which are expressed under normal growth conditions (31). A large number of genes coding for iron and hemin transporters, and two genes putatively coding for hemedependent transcriptional regulators, were identified in both the B. henselae and the B. quintana genomes.…”

“…In contrast, B. quintana contains only 18 repeat families, 12 of which are two-member families. The largest family in B. quintana contains seven tandemly repeated copies of the trwL gene located in one of the two operons coding for putative type IV secretion systems (12), and the second largest is a family of hemin-binding proteins (31).…”