EarthRef.org Digital Archive (ERDA) -- Cultivation of novel marine Fe-oxidizing bacteria from the Loihi Seamount

Description
Iron is one of the most abundant energy sources for lithotrophic organisms on Earth, yet very few cultures exist of Fe-oxidizing bacteria (FeOB) that can utilize Fe(II) as a sole energy source at circumneutral pH. Much of the work that has been done on FeOB is from freshwater habitats, so marine FeOB are even less well understood. In his keynote presentation for the First SBN Workshop, Dave Emerson shows that the advent of a variety of molecular techniques now make us much less dependent on culturing microbes to understand their diversity, abundance and role in the environment. At the same time those techniques underscore the importance of having representative isolates available in culture that can provide context for the interpretation of molecular methods. The culture of FeOB represents a special case in point, where specialized culturing conditions that mimic the host environment are essential to achieving success. We have focused studies on the extensive mats of (FeOB) at the summit of the Loihi Seamount (1100m deep) that are associated with low to intermediate temperature (10° to 65°C) vents whose fluids contain 10's to 100's of µM Fe(II). The mats contain 107 to 108 bacterial cells/cc and the morphology of the Fe-oxides is indicative of biological origins. We have isolated an obligately lithotrophic FeOB from Loihi, Mariprofundus ferroxydans. Phylogenetic analysis shows that M. ferroxydans is the first cultured representative of a proposed new Bacterial division, the zeta-Proteobacteria. Molecular evidence from Loihi, based on clone libraries and terminal restriction length polymorphism (tRFLP) analysis of 16S rRNA genes, indicate this lineage of FeOB is the most abundant inhabitant in the Fe-mats. Furthermore, this lineage is ubiquitous at diverse Fe(II)-driven ecosystems at hydrothermal vent sites throughout the Pacific.