Plesiomonas shigelloides is a gram-negative pathogen which can utilize heme as an iron source. In previous work, P. shigelloides genes which permitted heme iron utilization in a laboratory strain of Escherichia coli were isolated. In the present study, the cloned P. shigelloides sequences were found to encode ten potential heme utilization proteins: HugA, the putative heme receptor; TonB and ExbBD; HugB, the putative periplasmic binding protein; HugCD, the putative inner membrane permease; and the proteins HugW, HugX, and HugZ. Three of the genes, hugA, hugZ, and tonB, contain a Fur box in their putative promoters, indicating that the genes may be iron regulated. When the P. shigelloides genes were tested in E. coli K-12 or in a heme iron utilization mutant of P. shigelloides, hugA, the TonB system genes, and hugW, hugX, or hugZ were required for heme iron utilization. When the genes were tested in a hemA entB mutant of E. coli, hugWXZ were not required for utilization of heme as a porphyrin source, but their absence resulted in heme toxicity when the strains were grown in media containing heme as an iron source. hugA could replace the Vibrio cholerae hutA in a heme iron utilization assay, and V. cholerae hutA could complement a P. shigelloides heme utilization mutant, suggesting that HugA is the heme receptor. Our analyses of the TonB system of P. shigelloides indicated that it could function in tonB mutants of both E. coli and V. cholerae and that it was similar to the V. cholerae TonB1 system in the amino acid sequence of the proteins and in the ability of the system to function in high-salt medium.Plesiomonas shigelloides is a gram-negative bacterium associated with diarrheal disease in humans (4). The organism has been reported to cause several types of gastroenteritis, including acute secretory gastroenteritis (33), an invasive shigellosislike disease (35), and a cholera-like illness (55). Extraintestinal infections, such as meningitis, bacteremia (2), and pseudoappendicitis (13), are also associated with P. shigelloides infection.Many bacterial pathogens have iron transport systems that play a critical role in allowing the organism to establish an infection (for reviews, see references 31 and 41). Several bacterial pathogens, including P. shigelloides (9), obtain iron from heme or heme-containing compounds. Heme iron utilization systems have been examined in many gram-negative pathogens, including Vibrio cholerae (20,21,38), Vibrio vulnificus (30), Shigella dysenteriae (37, 60), Escherichia coli O157:H7 (54), Serratia marcescens (16, 26, 27), yersiniae (22, 50, 51, 53), Haemophilus (8,11,24,32), neisseriae (7,29,52,64), Pseudomonas (23,28,39), and Porphyromonas gingivalis (47). Many heme iron utilization systems studied to date require an outer membrane receptor which binds heme from the environment (for a review, see reference 58). TonB, with the aid of ExbBD, is thought to interact with the receptor to allow movement of heme into the periplasm. A periplasmic binding protein then moves the heme across th...

Vibrio alginolyticus, Vibrio fluvialis, andVibrio parahaemolyticus utilized heme and hemoglobin as iron sources and contained chromosomal DNA similar to severalVibrio cholerae heme iron utilization genes. A V. parahaemolyticus gene that performed the function of V. cholerae hutA was isolated. A portion of the tonB1locus of V. parahaemolyticus was sequenced and found to encode proteins similar in amino acid sequence to V. cholerae HutW, TonB1, and ExbB1. A recombinant plasmid containing the V. cholerae tonB1 and exbB1D1 genes complemented a V. alginolyticus heme utilization mutant. These data suggest that the heme iron utilization systems of the pathogenic vibrios tested, particularly V. parahaemolyticusand V. alginolyticus, are similar at the DNA level, the functional level, and, in the case of V. parahaemolyticus, the amino acid sequence or protein level to that of V. cholerae.