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Infect Immun, March 1998, p. 987-993, Vol. 66, No. 3
0019-9567/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.

Phase Variation of Hemoglobin Utilization in Neisseria gonorrhoeae

Ching-Ju Chen,1 Christopher Elkins,1,2 and P. Frederick Sparling1,2,*

Departments of Medicine1 and Microbiology and Immunology,2 School of Medicine, University of North Carolina, Chapel Hill, North Carolina 27599

Received 8 October 1997/Returned for modification 10 December 1997/Accepted 30 December 1997

Most Neisseria gonorrhoeae isolates are unable to use human hemoglobin as the sole source of iron for growth (Hgb-), but a minor population is able to do so (Hgb+). This minor population grows luxuriously on hemoglobin, expresses two outer membrane proteins of 42 kDa (HpuA) and 89 kDa (HpuB), and binds hemoglobin under iron-stressed conditions. In addition to the previously reported HpuB, we identified and characterized HpuA, which is encoded by the gene hpuA, located immediately upstream of hpuB. Expression of both proteins was found to be controlled at the translational level by frameshift mutations in a run of guanine residues within the hpuA sequence encoding the mature HpuA protein. The "on-phase" hemoglobin-utilizing variants contained 10 G's, while the "off-phase" variants contained 9 G's. Insertional hpuB mutants of FA19 Hgb+ and FA1090 Hgb+ no longer expressed HpuB but still produced HpuA. A polar insertional mutation of the upstream hpuA gene in FA1090 Hgb+ eliminated production of both HpuA and HpuB, whereas a nonpolar insertional mutant expressed HpuB only. Insertional mutagenesis of either hpuA or hpuB or both substantially decreased the hemoglobin binding ability of the FA1090 Hgb+ variant and prevented growth on hemoglobin plates. Therefore, both HpuA and HpuB were required for the utilization of hemoglobin for growth.

* Corresponding author. Mailing address: Department of Medicine, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599-7005. Phone: (919) 966-4468. Fax: (919) 966-5775. E-mail: zman{at}med.unc.edu.




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Copyright © 1998 by the American Society for Microbiology. All rights reserved.