Regulation of Oceanic Silicon and Carbon Preservation by Temperature Control on Bacteria Erica Zakhe

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Regulation of Oceanic Silicon and Carbon
Preservation by Temperature Control on
BacteriaErica ZakhemMicrobiology 405Fall 2003

• Kay D.Bidle, Maura Manganelli, Farooq Azam
• December 2002 Science VOL 298

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What they proposed

• Temperature control of marine bacteria action on
  diatoms influences the coupling of biogenic
  silica and organic carbon preservation.
• Low temperatures increase regeneration of organic
  matter by marine bacteria.
• Siliconcarbon ratio increases at lower
  temperatures.

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Common terms

• Diatoms
• extremely abundant in both freshwater and marine
  ecosystems. 25 of all organic carbon fixation on
  the planet is carried out by diatoms.
• Diatoms are a major food resource for marine and
  freshwater microorganisms and animal larvae, and
  are a major source of atmospheric oxygen.
• Diatoms are a major component of plankton,
  free-floating microorganisms of marine or
  freshwater environments.

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Thalassiosira weissflogii detriitus

• Diatom incubated with bacterial assemblages.
• Labeled with 14 C or 32 Si.

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Opal

• It is a popular gemstone.
• Opal is considered a mineraloid because this
  structure is not truly crystalline.
• It consists primarily of SiO2 and varying amounts
  of water. The amount of water varies from 5 -10
  and greater.
• Biogenic SiO2 accumulated in the ocean is called
  opal.

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Ectoproteases

• Proteases or peptidases are enzymes that catalyze
  the breakdown of peptide bonds (proteolysis).
• Ectoproteases are known to regulate cell-cell and
  cell-matrix interactions.

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Why temperature

• Several factors contribute to opal preservation
• Water column depth
• Opal rain rate
• Trace elements
• Aggregation
• Grazer characteristics
• Diatom morphology
• Temperature
• Dissolution rate increases 10 X for every 150C
• Opal accumulates in colder waters

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What they did

• Compared diatom particulate organic carbon (POC)
  and biogenic BSiO2 dissolution by bacteria
  isolated from Antarctic waters (-20C) to those
  from Californian waters (200C).
• Determined whether bacteria exhibit different
  degrees of POC decomposition and BSiO2
  dissolution throughout the water column, which
  can vary in water temperature ( 5, 15, 330C).

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Key aspects

• Sea water is unsaturated in BSiO2 and any exposed
  silica is used chemical dissolution.
• Diatoms protect the silica from dissolution by
  surrounding them with an organic matrix.
• Bacterial ectoproteases hydrolyze the organic
  matrix initiating silica dissolution at all
  temperatures and silica dissolution rates.
• Temperature affects bacteria and enzymatic
  activity and thus influences Si and C
  preservation.

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California waters
Antarctic waters
330C
150C
50C
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Figure 1

• Fig 1A
• Compares POC utilization and BSiO2 dissolution in
  Antarctic Vs. Californian isolates.
• Antarctic isolates preferentially preserved Si in
  comparison to C.
• POC decomposition is 6X as fast as BSiO2
  dissolution.

• Fig 1B
• Shows preferential regeneration of C over Si.
• Bacterial respiration was higher at 330C.
• At 50C bacteria neither respired nor assimilated
  POC before 3 days.
• Low ectoprotease activity and bacterial growth
  was exhibited at 50C.

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Overall

• 21 of diatom POC was regenerated and only 3.5
  BSiO2 after 7.5 daysFig 1A
• Temperature regulation of POC influenced Si
  preservationFig 1B
• Temperature regulation influences metabolism of
  bacteria.

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Figure 2

• Fig 2A
• Cell-specific protease activity in Antarctic and
  Californian isolates.
• Warmer temperatures elevated POC hydrolysis
  rates.
• Hydrolysis rates were elevated 3X in the first
  few days.

• Fig 2B
• Comparison between 5, 15, 330C.
• Proteolytic activity was 5X higher at 330C than
  at 150C within 1 day and growth rate was elevated
  15-30 X.
• No activity at 50C.

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Figure 3

• Fig 3A
• Temperature regulation of ectoprotease activity.
• Partially purified ectoproteases from temperate
  isolates.
• Optimum temperature was about 250C.

• Fig 3B
• Temperature regulation of ectoprotease activity.
• Cell-bound ectoproteases from Antarctic isolates.
  
• Optimum temperature was about 60C.

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330C
California
Antarctic
150C
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Figure 4

• Relates POC decomposition to BSiO2 dissolution.
• Temperate isolates Vs colder isolatesFig 4A
• 5, 15, 330C isolatesFig 4B
• Decoupling of C and Si regeneration is highly
  temperature dependent.
• The inhibition of BSiO2 dissolution requires
  substantial POC utilization.
• More C removal is required for silica dissolution
  at low temperatures resulting in a increase
  preservation of Si relative to C.

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Results

• This study demonstrated the importance of
  temperature regulation in the preservation of
  BSiO2 and POC.
• Stripping of the organic matrix and decoupling of
  Si and C preservation is enhanced in cold waters
  due to inhibition of microbial activity, combined
  with slower dissolution of exposed silica.

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• Systems experiencing seasonal temperature shifts
  may display greater variability in POC and BSiO2
  coupling.
• Si cycling, oceanic productivity, atmospheric CO2
  levels, and global climate changes are critical
  for predicting oceanic ecological processes.