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Abundant protein-containing particles in the sea
Aquatic Microbial Ecology
  • Richard A. Long, University of South Carolina - Columbia
  • Farooq Azam, University of California - San Diego
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The interaction of bacteria with particulate organic matter has implications for organic matter cycling and bacterial ecology in the ocean. Until recently, the focus has been on 'classical' particles visible by unaided eye (marine snow) or light microscopy. Recent discoveries of several new types of abundant particles, from sub-micrometer to sub-marine snow, are changing our ideas of the physical and chemical nature of the particle field with which pelagic bacteria interact. Previous workers have discovered polysaccharide-containing (Alcian Blue stainable) transparent exopolymer particles (TEP) ranging from 3 to 100s of micrometers. Looking for additional components of the sub-marine snow particle field, we took into consideration that since protein is a major component of biogenic organic matter, proteinaceous particles might also be abundant and important in bacteriaparticle interactions. We stained seawater with Coomassie Brilliant Blue G-250 (CBB), a protein stain, to reveal light to dark blue stained particles similar in shapes and size range to TEP. In samples filtered on Nuclepore filters, Coomassie Stained Particles (CSP) appeared globular, sheet- or string-like, while staining unfiltered water revealed 3-dimensional cloud-like shapes as well. Whether CSP are in fact TEP which also contain protein was tested by staining parallel samples with Alcian Blue and CBB (double staining a single sample was not possible since both dyes stain blue). CSP were 3 to 13 times more numerous and had up to 2 orders of magnitude greater area than TEP. Thus, while TEP and CSP may overlap, most CSP were distinct from TEP. Treatment of samples with Pronase E decreased CSP abundance and area by 78% and 96% respectively, confirming the proteinaceous nature of CSPs. The CSP abundance in coastal waters was 106 to 108 1-1, and their area was 102 to 104 mm2 1-1; both generally decreased with depth. Small particles were 2 to 3 orders of magnitude more abundant than large particles. Double staining with CBB and a fluorescent nucleic acid stain, DAPI, revealed that 20 to 40 % of CSP were colonized by bacteria. Since they contain protein, CSP may serve as a N source for bacteria and other organisms, and their production and utilization, which we did not study, may influence the flux and cycling of nitrogen in pelagic ecosystems.

Citation Information
Richard A. Long and Farooq Azam. "Abundant protein-containing particles in the sea" Aquatic Microbial Ecology Vol. 10 (1996) p. 213 - 221
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