6.6 Marine Microorganisms and Their Influence on Global Climate and Global Nutrient Recycling 141
6.6 Marine Microorganisms and Their
Influence on Global Climate
and Global Nutrient Recycling
The sea and oceans occupy 71% of the earth’s surface
and 97% of all the waters on earth (i.e., the biosphere).
The marine environment contains the greatest biologi-
cal diversity up to 11 m in ocean waters and up to 400
m in the sediments. At the same time, it has been esti-
mated that the biomass of microorganisms in seas and
oceans is more than gigatons, many times more than
other marine lives put together. On account of their
capacity for rapid growth, and their diverse ability to
bring about biochemical transformations, marine
microorganisms are major movers of global nutrient
cycles. It is not surprising that the activities of marine
microorganisms have global effects in the area of
global climate as well as the recycling of nutrients on
a global scale. This section will discuss these impor-
tant consequences of marine microbial activities on
planet earth (Arrigo 2005 ).
6.6.1 The Influence of Marine
Microorganisms on Global Climate
and Global Nutrient Recycling
In microorganisms living in environments such as sea
water where the osmotic pressure of the surrounding
liquid is higher than that of the cell, the osmoregulation
of the organisms is achieved by K+, especially KCl, as
well as one or more of a few low molecular weight
organic compounds known as “compatible solutes”
due to their compatibility in the cells where they are
found. A list of selected compatible solutes is given in
Table 6.4.
Apart from their osmoprotectant functions, they
also have other uses in the cell. For instance, they act
as cell reserves of carbon and nitrogen and are utilized
when necessary. They also act to protect the cell against
other forms of stress such as high or low temperature,FishZooplanktonAlgaeDOMBacteriaCiliatesHeterotrophic
flagellatesMicrobial loop
Microbial loop‘Grazer chain’Fig. 6.12 The microbial
loop (From Schulz 2006.
With permission)
Table 6.4 Some compatible solutes (Modified from
Welsh 2000. With permission)
Microbial group Compatible solute
Algae Sucrose
Glycerol
Mannitol
Proline
Glycine betaine
Dimethylsulfoniopropionate
Cyanobacteria Sucrose/trehalose
Glycine betaine
Glucosylglycerol
Phototrophic bacteria Sucrose/trehalose
Glycine betaine
Sulfate reducing bacteria Trhalose
Glycine betaine
Archaebacteria Glycine betaine
b-Glutamate