Myneni Satish C. B.

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Myneni
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Satish C. B.
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  • Article
    Natural organobromine in marine sediments : new evidence of biogeochemical Br cycling
    (American Geophysical Union, 2010-11-24) Leri, Alessandra C. ; Hakala, J. Alexandra ; Marcus, Matthew A. ; Lanzirotti, Antonio ; Reddy, Christopher M. ; Myneni, Satish C. B.
    Organobromine (Brorg) compounds, commonly recognized as persistent, toxic anthropogenic pollutants, are also produced naturally in terrestrial and marine systems. Several enzymatic and abiotic bromination mechanisms have been identified, as well as an array of natural Brorg molecules associated with various marine organisms. The fate of the carbon-bromine functionality in the marine environment, however, remains largely unexplored. Oceanographic studies have noted an association between bromine (Br) and organic carbon (Corg) in marine sediments. Even so, there has been no direct chemical evidence that Br in the sediments exists in a stable form apart from inorganic bromide (Brinorg), which is widely presumed conservative in marine systems. To investigate the scope of natural Brorg production and its fate in the environment, we probed Br distribution and speciation in estuarine and marine sediments using in situ X-ray spectroscopy and spectromicroscopy. We show that Brorg is ubiquitous throughout diverse sedimentary environments, occurring in correlation with Corg and metals such as Fe, Ca, and Zn. Analysis of sinking particulate carbon from the seawater column links the Brorg observed in sediments to biologically produced Brorg compounds that persist through humification of natural organic matter (NOM). Br speciation varies with sediment depth, revealing biogeochemical cycling of Br between organic and inorganic forms as part of the burial and degradation of NOM. These findings illuminate the chemistry behind the association of Br with Corg in marine sediments and cast doubt on the paradigmatic classification of Br as a conservative element in seawater systems.
  • Article
    Overexpression and characterization of an iron storage and DNA-binding Dps protein from Trichodesmium erythraeum
    (American Society for Microbiology, 2006-04) Castruita, M. ; Saito, Mak A. ; Schottel, P. C. ; Elmegreen, L. A. ; Myneni, Satish C. B. ; Stiefel, E. I. ; Morel, Francois M. M.
    Although the role of iron in marine productivity has received a great deal of attention, no iron storage protein has been isolated from a marine microorganism previously. We describe an Fe-binding protein belonging to the Dps family (DNA binding protein from starved cells) in the N2-fixing marine cyanobacterium Trichodesmium erythraeum. A dps gene encoding a protein with significant levels of identity to members of the Dps family was identified in the genome of T. erythraeum. This gene codes for a putative DpsT. erythraeurm protein (Dpstery) with 69% primary amino acid sequence similarity to Synechococcus DpsA. We expressed and purified Dpstery, and we found that Dpstery, like other Dps proteins, is able to bind Fe and DNA and protect DNA from degradation by DNase. We also found that Dpstery binds phosphate, like other ferritin family proteins. Fe K near-edge X-ray absorption of Dpstery indicated that it has an iron core that resembles that of horse spleen ferritin.