321
Photoinduced and Microbial Degradation
equal during the incubation of reduced sediments (Fig. 8c,d) (Roden and Wetzel
1996). Therefore, the occurrence and the nature of organic matter and its fermentation or disintegration products are key factors for the production of CO 2 , CH 4
and other end products in the aquatic environments.
4.3 Temperature
The growth of homoacetogenic bacteria and methanogenic archaea significantly depends on the ambient temperature (Table 2) (Kotsyurbenko et al. 2001;
Kotsyurbenko et al. 2007; Thebrath et al. 1993; Westermann 1994; Kotsyurbenko
et al. 1995; Simankova et al. 2000; Zinder 1990). It is shown that the microbial function is typically much higher at low temperature (5.0–7.0 °C), showing
maximum bacterial abundance (3.9–7.9 × 10 5 cells ml −1 , mean = 6.4) and biomass (4.0–6.7 μg C L −1 , mean = 5.2). Lower values (1.3–2.5 × 10 5 cells ml −1 ,
mean = 1.8; and 1.3–2.4 μg C L −1 , mean = 1.7, respectively) have been found
at higher temperature (7.5–11.1 °C) in open water in Lake La Caldera (Carrillo
et al. 2002). Homoacetogenic bacteria and methanogenic archaea can consume H 2
over a temperature range of 1–35 °C, but their optimum temperature is often high
(~20–30 °C, Table 2). Homoacetogenic A. bakii, A. tundrae and the methanogenic
strain MSB have shown the largest temperature range for optimal H 2 consumption,
which is extending at least from 4 to 30 °C (Kotsyurbenko et al. 2001). However,
A. fimetarium, A. paludosum and strain MSP become less efficient toward H 2
consumption when the temperature decreases below 10 °C (Kotsyurbenko et al.
2001). Low temperatures are often favorable for acetogenesis, which becomes a
quantitatively important process in anaerobic environments (Nozhevnikova et al.
1994; Kotsyurbenko et al. 1993).
At low temperature, homoacetogenic bacteria outcompetes methanogens for
H 2 in laboratory experiments (Conrad et al. 1989; Kotsyurbenko et al. 1993).
According to kinetic estimations, homoacetogens have a much higher growth
rate at low temperature than methanogens (Kotsyurbenko et al. 1996). It is also
shown that the contribution of methanogenic bacterial associations (MBA) to
H 2 -dependent methanogenesis is enhanced (it reaches 99 %) when the temperature is shifted from 30 to 17 °C, or when the soil is planted with rice (Conrad
et al. 1989a, b). This enhancement is partially due to an increased utilization of
dissolved H 2 by chloroform-insensitive non-methanogenic bacteria, most probably homoacetogens, so that CH 4 production is almost completely restricted to
H 2 -syntrophic MBA. Acetate is the precursor of approximately two-thirds of the
methane produced in mesophilic (30–40 °C) and thermophilic (45–65 °C) anaerobic bioreactors (Zinder 1990). Increasing the incubation temperature of two
swamp slurries from 2 to 37 °C resulted in a 8- to 18-fold increase in the H 2 partial pressure (Westermann 1994). The study also shows that the concentration of
volatile fatty acids remained fairly constant except for butyrate, which decreased
with increasing temperature.
Photoinduced and Microbial Degradation
equal during the incubation of reduced sediments (Fig. 8c,d) (Roden and Wetzel
1996). Therefore, the occurrence and the nature of organic matter and its fermentation or disintegration products are key factors for the production of CO 2 , CH 4
and other end products in the aquatic environments.
4.3 Temperature
The growth of homoacetogenic bacteria and methanogenic archaea significantly depends on the ambient temperature (Table 2) (Kotsyurbenko et al. 2001;
Kotsyurbenko et al. 2007; Thebrath et al. 1993; Westermann 1994; Kotsyurbenko
et al. 1995; Simankova et al. 2000; Zinder 1990). It is shown that the microbial function is typically much higher at low temperature (5.0–7.0 °C), showing
maximum bacterial abundance (3.9–7.9 × 10 5 cells ml −1 , mean = 6.4) and biomass (4.0–6.7 μg C L −1 , mean = 5.2). Lower values (1.3–2.5 × 10 5 cells ml −1 ,
mean = 1.8; and 1.3–2.4 μg C L −1 , mean = 1.7, respectively) have been found
at higher temperature (7.5–11.1 °C) in open water in Lake La Caldera (Carrillo
et al. 2002). Homoacetogenic bacteria and methanogenic archaea can consume H 2
over a temperature range of 1–35 °C, but their optimum temperature is often high
(~20–30 °C, Table 2). Homoacetogenic A. bakii, A. tundrae and the methanogenic
strain MSB have shown the largest temperature range for optimal H 2 consumption,
which is extending at least from 4 to 30 °C (Kotsyurbenko et al. 2001). However,
A. fimetarium, A. paludosum and strain MSP become less efficient toward H 2
consumption when the temperature decreases below 10 °C (Kotsyurbenko et al.
2001). Low temperatures are often favorable for acetogenesis, which becomes a
quantitatively important process in anaerobic environments (Nozhevnikova et al.
1994; Kotsyurbenko et al. 1993).
At low temperature, homoacetogenic bacteria outcompetes methanogens for
H 2 in laboratory experiments (Conrad et al. 1989; Kotsyurbenko et al. 1993).
According to kinetic estimations, homoacetogens have a much higher growth
rate at low temperature than methanogens (Kotsyurbenko et al. 1996). It is also
shown that the contribution of methanogenic bacterial associations (MBA) to
H 2 -dependent methanogenesis is enhanced (it reaches 99 %) when the temperature is shifted from 30 to 17 °C, or when the soil is planted with rice (Conrad
et al. 1989a, b). This enhancement is partially due to an increased utilization of
dissolved H 2 by chloroform-insensitive non-methanogenic bacteria, most probably homoacetogens, so that CH 4 production is almost completely restricted to
H 2 -syntrophic MBA. Acetate is the precursor of approximately two-thirds of the
methane produced in mesophilic (30–40 °C) and thermophilic (45–65 °C) anaerobic bioreactors (Zinder 1990). Increasing the incubation temperature of two
swamp slurries from 2 to 37 °C resulted in a 8- to 18-fold increase in the H 2 partial pressure (Westermann 1994). The study also shows that the concentration of
volatile fatty acids remained fairly constant except for butyrate, which decreased
with increasing temperature.