Environmental Microbiology Lecture 6

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Environmental Microbiology Lecture 6

• Bacterial production and biomass

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Microbial loop
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Why do we care for bacterial production?
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Bacterial abundance in marine environments
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How to determine bacterial production?
P production µ growth rate (d-1) B biomass
P µB

• Biomass (mg C/L-1)
• measuring cell abundance and cell volume by
  microscopy and flow cytometry.
• Production (mg C/L-1/d-1)
• measuring metabolic activities by radiolabeled
  isotope incorporation.

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How to measure biomass?

• Epifluorescence microscopy
• bacterial abundance (cells ml-1)
• Filter seawater onto nucleopore polycarbonate
  filter (typically 0.2 µm).
• Stain bacterial cells using nucleic acid or
  protein stain (e.g. DAPI or acridine orange).
• Visualize cells by epifluorescence microscopy.
• Count cells and measure cell sizes.

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How to measure biomass?

• Epifluorescence microscopy
• bacterial volume (µm3 cell-1)
• Measure the diameter of 300-400 cells per samples
  for statistical precision
• Calculate the cell volume using V 4/3 pr3

So, Biomass (µm3 ml-1) abundance (cell ml-1) X
volume (µm3 cell-1)
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How to measure biomass?

• Flow cytometry
• Greater sensitivity and sample sizes
• Provides cell abundance and sometimes estimated
  cell sizes
• Sort out live and dead cells

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Carbon conversion factor for biomass (µm3 ml-1
or cells ml-1 ? mg C ml-1)
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Vertical bacterial biomass distribution in the
ocean
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How to determine bacterial production?
P production µ growth rate (d-1) B biomass
P µB

• Biomass (mg C/L-1)
• measuring cell abundance and cell volume by
  microscopy and flow cytometry.
• Production (mg C/L-1/d-1)
• measuring metabolic activities by radiolabeled
  isotope incorporation.

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Environmental factors controlling bacterial
production

• Resources (bottom up) inorganic and organic
  substrates
• Predation (top down) control for biomass
  accumulation, thereby influencing growth rate
  determinations
• Temperature
• Sun light (radiation) photoreaction of DOM

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How to measure bacterial production?
Most direct method is to measure changes in cell
abundance and volume (biomass) over time in the
absence of predation.
Common methods (? biomass/time)

• 3H-thymidine incorporation into DNA
• 3H/14C-leucine incorporation into Protein
• 3H-adenine incorporation into DNA and RNA

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How to measure bacterial production?
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Pathways of radioisotope incorporation in
bacterial biomass
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Conversion factors for bacterial production

• Derivative approach
• CFder ?(N0/T0)
• Modified derivative approach
• CFmod µ (eB/eb)
• Cumulative approach
• CFcum dN/dTdR

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Vertical profiles of bacterial production in the
ocean
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Overall bacterial biomass production in the ocean