Pseudoalterobactin A and B, new siderophores excreted by marine bacterium Pseudoalteromonas sp. KP20-4.

Siderophores are relatively low-molecular-weight compounds that typically have a very high affinity constant (1025-1050)1) for iron (Fe3+), which is an essential element for most microorganisms owing to its importance in a variety of biochemical reactions. The role of siderophores is to scavenge extracellular iron from the environment and transport it into microbial cells. Hundreds of siderophores have been isolated from terrestrial, especially pathogenic, microorganisms, and their biosyntheses and ironsequestering systems have been enthusiastically studied.2-4) In spite of the high abundance of iron in the earth's crust, the dissolved iron concentration is particularly low