MEMBRANE-PROTEIN EXPRESSION BY ACTINOBACILLUS-ACTINOMYCETEMCOMITANS IN RESPONSE TO IRON AVAILABILITY

Iron-limited growth conditions under anaerobiosis were established for Actinobacillus actinomycetemcomitans strains Y4, JP2, and 75 by use o f the ferrous ion chelator 2,2'-dipyridyl. Growth inhibition was rever sible with both ferrous and ferric iron sources. Sarcosyl-insoluble me mbrane fractions of iron-stressed anaerobic A. actinomycetemcomitans c ultures revealed a similar iron-repressible protein of approximately 7 0 kDa in A. actinomycetemcomitans strains Y4, JP2, and 75. This 70-kDa protein was recognized by serum from localized juvenile periodontitis patients and a periodontally healthy subject. This suggested that the 70-kDa iron-repressible protein may be expressed in vivo. When A. act inomycetemcomitans was grown under aerobic conditions, the ferric iron chelator, ethylenediamine di(o-hydroxyphenylacetic acid) (EDDA) was u tilized for growth limitation. EDDA inhibition was reversible in strai n Y4 with ferrous and ferric iron sources. An iron-repressible protein of approximately 70 kDa was also noted in iron-stressed aerobic cultu res. The 70-kDa protein may be involved in iron transport by A. actino mycetemcomitans. Preliminary experiments were performed to examine pot ential iron transport systems for A. actinomycetemcomitans. Production of the two most common chemical types of siderophore was not detected in A. actinomycetemcomitans culture supernatants. Iron-starved A. act inomycetemcomitans cells did not bind transferrin or lactoferrin in a dot blot assay.