4.7 Biofilms
89
Hydrogen
sulphide
Oxygen
Fluid
Biofilm
Fig. 4.34 Left: Three groups of microorganisms with different metabolisms are distributed within
a biofilm, concentrating in areas that suit their needs – and match their color (Stewart and Franklin,
2008). The simulated segregation pattern between cooperators and cheaters (red and blue) under
conditions of radial (center) and vertical (right) growth and high (upper row), moderate (middle
row), and low (lower row) growth substrate availability (Nadell et al, 2010)
Different species may be unevenly distributed within a biofilm when they concentrate in locations most suitable to their abilities and needs. In a simple example
schematized in the left panels of Fig. 4.34, hydrogen sulfide diffuses from the left
and oxygen from the right. Accordingly, the abundance of aerobic bacteria, colored
brown in the picture, rapidly decays from right to left, while the density of sulphatereducing bacteria, colored yellow, decreases in the opposite direction, in parallel to
the decay of concentrations of, respectively, oxygen and hydrogen sulfide, shown in
the lower panel. Sulphide-oxidizing bacteria, colored blue, prefer the blue area in
the lower panel where both of the chemicals they need are present.
Segregation may be social, driven by motives not unfamiliar to us humans. Bacteria often depend on insoluble substrates for growth, and secrete digestive enzymes,
which degrade such substrates into soluble units. These soluble, nutrient-rich products can be captured by neighboring cells, which do not invest themselves in the
production of digestive enzymes. Nadell et al (2010) built up a biofilm growth model
imitating such a situation. It includes two cell lineages: exploitative that devote all
resources to growth, and cooperative that secrete a diffusible compound benefitting
all other cells in the vicinity. The cell’s growth rate is proportional in this model to the
local substrate concentration when it is low, and saturates at high concentration, according to the common Michaelis–Menten kinetics. Once a cell reaches a maximum
size, it divides, and cells move passively due to the forces exerted by their neighbors
89
Hydrogen
sulphide
Oxygen
Fluid
Biofilm
Fig. 4.34 Left: Three groups of microorganisms with different metabolisms are distributed within
a biofilm, concentrating in areas that suit their needs – and match their color (Stewart and Franklin,
2008). The simulated segregation pattern between cooperators and cheaters (red and blue) under
conditions of radial (center) and vertical (right) growth and high (upper row), moderate (middle
row), and low (lower row) growth substrate availability (Nadell et al, 2010)
Different species may be unevenly distributed within a biofilm when they concentrate in locations most suitable to their abilities and needs. In a simple example
schematized in the left panels of Fig. 4.34, hydrogen sulfide diffuses from the left
and oxygen from the right. Accordingly, the abundance of aerobic bacteria, colored
brown in the picture, rapidly decays from right to left, while the density of sulphatereducing bacteria, colored yellow, decreases in the opposite direction, in parallel to
the decay of concentrations of, respectively, oxygen and hydrogen sulfide, shown in
the lower panel. Sulphide-oxidizing bacteria, colored blue, prefer the blue area in
the lower panel where both of the chemicals they need are present.
Segregation may be social, driven by motives not unfamiliar to us humans. Bacteria often depend on insoluble substrates for growth, and secrete digestive enzymes,
which degrade such substrates into soluble units. These soluble, nutrient-rich products can be captured by neighboring cells, which do not invest themselves in the
production of digestive enzymes. Nadell et al (2010) built up a biofilm growth model
imitating such a situation. It includes two cell lineages: exploitative that devote all
resources to growth, and cooperative that secrete a diffusible compound benefitting
all other cells in the vicinity. The cell’s growth rate is proportional in this model to the
local substrate concentration when it is low, and saturates at high concentration, according to the common Michaelis–Menten kinetics. Once a cell reaches a maximum
size, it divides, and cells move passively due to the forces exerted by their neighbors