Studies of Iron-Uptake Mechanisms in Two Bacterial Species of the Shewanella Genus Adapted to Middle-Range (Shewanella putrefaciens) or Antarctic (Shewanella gelidimarina) Temperatures

Iron(III)‐uptake mechanisms in bacteria indigenous to the Antarctic, which is the most Fe‐deficient continent on Earth, have not been extensively studied. The cold‐adapted, Antarctic bacterium, Shewanella gelidimarina, does not produce detectable levels of the siderophore, putrebactin, in the supernatant of FeIII‐deprived cultures. This is distinct from the putrebactin‐producing bacterium from the same genus, Shewanella putrefaciens, which is adapted to middle‐range temperatures. The production of putrebactin by S. putrefaciens is optimal, when the pH value of the medium is 7.0. According to the strong positive response from whole cells in the Chrome Azurol S (CAS) agar diffusion assay, Shewanella gelidimarina appears to produce cell‐associated siderophores. In the RP‐HPLC trace of an FeIII‐loaded extract from the cell‐associated components of S. gelidimarina cultured in media with [FeIII] ca. 0 μM, a peak appears at [MeCN] ca. 77%, which decreases in intensity in a parallel experiment in which [FeIII] ca. 5 μM, and is barely detectable in FeIII‐replete media ([FeIII] ca. 20 μM). The FeIII‐dependence of this peak suggests that the attendant species, which is significantly more hydrophobic than putrebactin (RP‐HPLC elution: [MeCN] ca. 14%), is associated with FeIII‐management in S. gelidimarina. This study highlights the diversity in FeIII‐uptake mechanisms in Shewanella species adapted to different environmental and thermal niches.