AUTHOR=Maltz Michele , Levarge Barbara L., Graf Joerg 

TITLE=Identification of iron and heme utilization genes in Aeromonas and their role in the colonization of the leech digestive tract

JOURNAL=Frontiers in Microbiology

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2015.00763

DOI=10.3389/fmicb.2015.00763

ISSN=1664-302X

ABSTRACT=<p>It is known that many pathogens produce high-affinity iron uptake systems like siderophores and/or proteins for utilizing iron bound to heme-containing molecules, which facilitate iron-acquisition inside a host. In mutualistic digestive-tract associations, iron uptake systems have not been as well studied. We investigated the importance of two iron utilization systems within the beneficial digestive-tract association <italic>Aeromonas veronii</italic> and the medicinal leech, <italic>Hirudo verbana</italic>. Siderophores were detected in <italic>A. veronii</italic> using chrome azurol S. Using a mini Tn5, a transposon insertion in <italic>viuB</italic> generated a mutant unable to utilize iron using siderophores. The <italic>A. veronii</italic> genome was then searched for genes potentially involved in iron utilization bound to heme-containing molecules. A putative outer membrane heme receptor (<italic>hgpB</italic>) was identified with a transcriptional activator, termed <italic>hgpR</italic>, downstream. The <italic>hgpB</italic> gene was interrupted with an antibiotic resistance cassette in both the parent strain and the <italic>viuB</italic> mutant, yielding an <italic>hgpB</italic> mutant and a mutant with both iron uptake systems inactivated. <italic>In vitro</italic> assays indicated that <italic>hgpB</italic> is involved in utilizing iron bound to heme and that both iron utilization systems are important for <italic>A. veronii</italic> to grow in blood. <italic>In vivo</italic> colonization assays revealed that the ability to acquire iron from heme-containing molecules is critical for <italic>A. veronii</italic> to colonize the leech gut. Since iron and specifically heme utilization is important in this mutualistic relationship and has a potential role in virulence factor of other organisms, genomes from different <italic>Aeromonas</italic> strains (both clinical and environmental) were queried with iron utilization genes of <italic>A. veronii</italic>. This analysis revealed that in contrast to the siderophore utilization genes heme utilization genes are widely distributed among aeromonads. The importance of heme utilization in the colonization of the leech further confirms that symbiotic and pathogenic relationships possess similar mechanisms for interacting with animal hosts.</p>