The Ocean as a Microbial Habitat

Matthew ChurchMarine Microplankton Ecology

OCN 626/Fall 2008

The Ocean as a Habitat

• Energy, nutrients, and life

• Description of the physical, chemical, and biological environment

• What does life require?– Energy– Nutrients (carbon, nitrogen, phosphorus, oxygen,

sulfur, etc., etc.)– Electron donor-a source of reductant– Electron acceptor- required for respiration

• Common habitat controls microorganism distributions and abundance– Light– Nutrients– Temperature– Pressure– Redox environment

Energy flows, matter cycles

Sources of energy for life in the sea

• Light-aside from hydrothermal vents, sunlight is the ultimate energy source for life in the sea (phototrophy).

• Chemical-both organic and inorganic compounds (chemotrophy).

H2S Glucose

Nutrient sources

• Nitrogen: protein, nucleic acids– NO3

-, NO2-, N2, NH3, organic N

• Phosphorus: nucleic acids, lipids– PO4

3-, organic P

• Carbon: nucleic acids, protein, lipids, carbohydrates, etc.– CO2, organic C

• Sulfur: amino acids, protein, lipids– SO4

2-, S, H2S, organic S

• Light, Salinity, Nutrients, Temperature, Pressure

Spatial gradients in the marine environment

Time-space scales of physical processes

B

P

ZF

From T. Dickey

Scales of variability are importantNote that increasing time scales generally

correspond to increasing space

scales

•Generation time of a tree:

years

•Generation time of

microbe:minutes to

days

Temperature-salinity plot from Station ALOHA showing the time-dependent changes in physical ocean properties. Note greater variability in physical

environment in upper 200 m; deep sea (>1000 m) largely invariant with time.

NOAA-NESDIS-National Oceanographic Data Center

~30X variation in temperature in the surface ocean

~4X variation in temperature in the deep sea

Sea Surface Temperature Chl a (°C) (mg m-3)

The ocean is stirred more than mixed

Yoder, 1994

Spatial discontinuities at various scales (basin, mesoscale, microscale) in the ocean habitat play an important role in controlling the growth of microorganisms.

Shelford’s Law of Tolerances:The distribution and abundance of an

organism will be controlled by that environmental factor for which the species has

the narrowest range of tolerance.

Oceans

Organisms have evolved specific tolerances to habitat variables (light, temperature, nutrients,

pH, oxygen, salinity)Group

ClassificationMinimum Optimum Maximum

Psychrophile <0 10-15 >20

Psychrotroph 0 15-20 >25

Mesophile 10-15 30-40 <45

Thermophile 45 50-85 >100

Most organisms in the oceans are psychrophiles and mesophiles

Oceans

Div

isio

ns p

er d

ay

Temperature (oC)

Temperature plays an important role in

controlling plankton growth and distributions. In this example, diatoms

have a wider range of optimal temperatures

than flagellated phytoplankton.

Which group of plankton would be predicted to

have a more cosmopolitan distribution?

Light transmission through the atmosphere and ocean

Visible

UV

Infrared

Energy impinging on the Earth’s surface is most

intense in visible portion of the spectrum

Profile of irradiance with depth

Data from Station ALOHA

Downwelling irradiance (W cm-2 nm-1)

0 20 40 60 80 100

De

pth

(m

)

0

20

40

60

80

100

120

140

160

412 nm510 nm 665 nm

Downwelling irradiance (W cm-2 nm-1)

0.1 1 10 100 1000

De

pth

(m

)

0

20

40

60

80

100

120

140

160

412 nm510 nm 665 nm

In the blue-green regions of the visible spectrum, sunlight penetrates deep into the ocean

Differences in growth as a

function of light energy by

4 isolates of Prochlorococcus

Vertical Profiles of Nutrients

Nutrient distributions with depth (pressure) at Station ALOHA

NOAA-NESDIS-National Oceanographic Data Center

Nutrient availability is governed by physics: mixing, upwelling, advection, diffusion AND biology: the balance between assimilation and remineralization

7 years of ocean chlorophyll from satellites

Mean

Maximum

Minimum

High latitudes are highly variable, central

gyres more stable

Spatially coherent interannual variability in selected ecosystems (equator for example) but most ocean

ecosystems appear highly variable in space and time

Biological variability in space and time

The mesopelagic zone is an important

region of decomposition.

Photosynthetically derived material

produced in the well-lit upper ocean sinks

to the ocean’s interior-microbes in the mesopelagic rely

on this sinking material for energy.

NO3- + NO2

- (mol L-1)

0 10 20 30 40 50

De

pth

(m

)0

1000

2000

3000

4000

PacificAtlantic

Basin scale differences in

nutrient concentrations

controlled by biology (decomposition) and

physics (thermohaline

circulation)

The bathypelagic

Barophilic (or piezophilic) microorganisms

• Barophilic microorganisms grow optimally at pressures in excess of 1 atm.

• Low temperatures and high pressures both solidify lipids (cell membranes).

• Microorganisms can adapt to changes in pressure by increasing or decreasing the fluidity of cell membranes through changes in fatty acid composition (through production of unsaturated fatty acids)

Yayanos et al. (1981) PNAS

Interactive influences of pressure and temperature on the growth of a bacterium isolated from Mariana Trench