Abstract
Protocatechuic acid, or 3,4-dihydroxybenzoic acid, is produced by both soil and marine bacteria in the free form and as the iron binding component of the siderophore petrobactin. The soil bacterium, Bacillus thuringiensis kurstaki ATCC 33679, contains the asb operon, but does not produce petrobactin. Iron restriction resulted in diminished B. thuringiensis kurstaki ATCC 33679 growth and the production of catechol(s). The gene product responsible for protocatechuic acid (asbF) and its receptor (fatB) were expressed during stationary phase growth. Gene expression varied with growth temperature, with optimum levels occurring well below the Bacillus anthracis virulence temperature of 37 °C. Regulation of protocatechuic acid suggests a possible role for this compound during soil growth cycles.
Highlights
Iron uptake mechanisms in members of the Bacillus cereus sensu lato group have emerged as areas of interest in the identification of virulence factors and as diagnostic tools
B. thuringiensis was cultured at 25 °C, 30 °C and 37 °C in iron restricted medium, which have proven successful in the generation of siderophore in Bacillus species [2,17]
The lower temperature would represent conditions associated with the soil cycle, while elevated temperatures are associated with virulence factor expression in B. anthracis in humans [18]
Summary
Iron uptake mechanisms in members of the Bacillus cereus sensu lato group have emerged as areas of interest in the identification of virulence factors and as diagnostic tools. Regardless of the growth conditions, B. anthracis produces large amounts of 3,4-dhb, or protocatechuic acid, which has not been demonstrated to reverse iron restricted growth [6] while 2,3-dhb has been demonstrated to act as a siderophore for some microbes [7]. It is unclear how the gene responsible for 3,4-dhb production, asbF, is regulated under these conditions, as it was not measured in the previous. We hypothesized that 3,4-dhb is produced by B. thuringiensis ATCC33679 during growth in iron limited environments Within the soil, this compound could provide an iron reservoir for growing bacteria. These pockets would provide the organisms with an area that was limited in competition because of the antimicrobial and antifungal activities
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