Souren (1998), in a Comment to our paper, notes that there are important mechanistic similarities between Mn and Co oxidation by fungi, and the oxidation ...
Geochimica et Cosmochimica Acta, Vol. 62, No. 2, pp. 359, 1998 Copyright © 1998 Elsevier Science Ltd Printed in the USA. All rights reserved 0016-7037/98 $19.00 1 .00
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REPLY
Reply to the Comment by A. W. M. G. Souren on ‘‘Oxidation of cobalt and manganese in seawater via a common microbially catalyzed pathway’’ JAMES W. MOFFETT Department of Marine Chemistry and Geochemistry, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
The Comment of Souren (1998) is nevertheless an interesting new perspective for marine geochemists. Fungi may play an important role in Mn cycling in benthic environments containing high levels of terrestrial plant material, particularly given the high ratios of fungal to bacterial biomass under certain conditions. The role of fungi on oxide mineralogy, trace element incorporation, and the influence of Mn availability on organic matter degradation in nearshore sediments are important topics for future research.
Souren (1998), in a Comment to our paper, notes that there are important mechanistic similarities between Mn and Co oxidation by fungi, and the oxidation described in our paper. These similarities are intriguing, and Souren (1998) goes on to argue that Co and Mn oxidation in Waquoit Bay could be mediated by fungi. However, a microscopic examination of suspended particulate matter collected from Waquoit Bay during our original study showed no evidence of fungal hyphae (W. Ghiorse, Cornell University, pers. commun.). Moreover, enrichments of Waquoit Bay seawater prepared by W. Ghiorse, revealed the presence of at least three distinct Mn-oxidizing bacteria, one tentatively identified as a pseudomonad. The overwhelming preponderance of microscopic data on biologically catalyzed Mn oxidation in seawater has revealed that bacteria are responsible, as reviewed by Tebo (1998) in an accompanying Comment. The argument of Souren (1998) is that the mechanistic similarities provide the strongest evidence for fungal mediation in our system. Yet bacteria can also oxidize cobalt. Tebo and Lee (1994) have shown that a marine Mn-oxidizing Bacillus spore can oxidize Co, and Lienemnann et al. (1997) have identified Co and Mn precipitates on freshwater Mn oxidizing bacteria collected from the field. What is lacking is a competitive inhibition study between Co and Mn on a Mn oxidizing bacteria in culture, as has been performed by us in the water column and cited by Souren (1998) for terrestrial fungi.
REFERENCES Lee Y. and Tebo B. M. (1994) Cobalt oxidation by the marine Mn(II)oxidizing Bacillus strain SG-1. Appl. Environ. Microbiol. 60, 2949 – 2957. Lienemann C., Taillefert M., Perret D. and Gaillard J. (1997) Association of cobalt and manganese in aquatic systems: Chemical and microscopic evidence. Geochim. Cosmochim. Acta 61, 1437–1446. Souren A. W. M. G. (1998) Comment on ‘‘Oxidation of cobalt and manganese in seawater via a common microbially catalyzed pathway’’ by J. W. Moffett and J. Ho. Geochim. Cosmochim. Acta 62, 357–358 (this issue). Tebo B. M. (1998) Comment on the Comment by A. W. M. G. Souren on ‘‘Oxidation of cobalt and manganese in seawater via a common microbially catalyzed pathway.’’ Geochim. Cosmochim. Acta 62, 351–355 (this issue).
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