Volume 6, Spring 2008 - Saddleback College

38
Saddleback Journal of Biology
Spring 2008
Fall 2007 Biology 3A Abstracts
Gas Production (ml)
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
pH1 pH3 pH5 pH7 pH9
Figure 1. Mean gas production is 0.14 ± 0.02 mls (±se)
in pH1: 0.02 ± 0.02 mls in pH3, 0.69 ± 0.12 mls in
pH5, 0.56 ± 0.13 mls in pH7, and 0.64 ± 0.13 mls in
pH9 (±se). Maximum production of gases was
observed in pH5, 0.69 ± 0.12 mls (±se), and minimum
production was in pH3, 0.02 ± 0.02 mls (±se). Gas
production in the fermentation of E. coli significantly
differs between different pH groups (p=0.0002,
ANOVA). Error bars show the standard errors.
Decrease of the volume of gas production
For four tubes in pH 3 and one tube in pH 1,
the decrease in volume of gas production between 24
hours and 48 hours after the initiation of the
fermentation in E. coli was observed. Also, mean gas
production after 48 hours in pH 3 is smaller than after
24 hours while the increases of gas production were
observed for other pH groups (Table. 1). Mean gas
production of 24 hours after the incubation was 0.11 ±
0.02 mls (±se), and mean of 48 hours after was 0.02 ±
0.02 mls (±se).
Table 1. Mean gas production in milliliters after 24
hours and 48 hours of Escherichia coli fermentation in
different pH groups (pH 1, 3, 5, 7, and 9). N=5 for
each pH. The incubation was carried out at 36 ºC. The
values were expressed as means ± se.
Gas Production (ml)
Time pH 1 pH 3 pH 5 pH 7 pH 9
Also, gas production in higher pH (pH 5-9) was
greater than in lower pH (pH 1-3) (Fig. 1). Although
the maximum production was observed in pH 5, 0.69 ±
0.12 mls (±se), there were much greater gas production
in pH 7 and 9 than pH 1 and 3. From these results
show that higher pH (5-9) allows E. coli to produce
larger amount of H 2 and CO 2 , and, thus, optimum pH
in this study. These pH values can include the result of
Chitteibabu, et al. (2006) that optimum pH is 6.0 for
maximum yield of hydrogen in Escherichia coli BL-
21. In another study, optimum pH is 6.2 with glucose
and a mixed culture (Oh et al., 2003). Furthermore,
Glass et al. (1992) concluded that E. coli grew well at
all alkaline pH values (to pH 9.0). Thus, E. coli has
wide range of optimum pH for the fermentation, pH 5-
9, and does not carry out the fermentation effectively in
pH 1 and 3. The results in this study are reliable
because they match previous studies.
In this study, pH 5 showed the maximum
production, 0.69 ± 0.12 mls (±se) although lower pH
than pH 5 showed a less amount of gas production,
0.14 ± 0.02 mls (±se) in pH 1 and 0.02 ± 0.02 mls in
pH 3. The gas production rapidly decreased from pH 5
to pH 3 (Fig. 1). These results show that there is a
border line between pH 3 and 5 and suggest that E. coli
cannot carry out the fermentation efficiently at the
lower pH than that border line. Jordan et al. (1999)
also showed that poorer pH homeostasis was most
evident below pH 5. However, the minimum gas
production was not in pH 1. The minimum gas
production was observed in pH 3 in this study as it is
between 4.0 and 4.5 in the study of Glass et al. (1992).
Thus, the gas production in E. coli fermentation is not
proportional to pH values. The fermentation of E. coli
is regulated by many factors such as a fermentating
substrate, pH, redox potential, and temperature
(Bragramyan and Trchounian, 2003). Also, E. coli (K-
12 and O157:H7) produce many organic compounds,
converting glucose to acetate, formate, and ethanol
(Diez-Gonzalez and Russell, 1997). The combination
of these factors and processes gives the different results
in each time. However, further analysis is required for
the details of the combination of them.
24 hours 0.12±0.02 0.11±0.02 0.56±0.08 0.43±0.12 0.51±0.13
Minimum pH for growth and Internal pH
48 hours 0.14±0.02 0.02±0.02 0.69±0.12 0.56±0.13 0.64±0.13
There are many enzymes that play a role in
mixed-acid fermentation of E. coli. Enzyme repression
Discussion
and inhibition of their activity by oxygen regulate the
pH dependence and optimum pH
gateway of mixed-acid fermentation because these
enzyme function only under aerobic or anaerobic
Gas production in the fermentation of E. coli condition (Bragramyan and Trchounian, 2003). From
showed that there are significant differences between results, the gas production in the fermentation of E.coli
different pH groups (Fig. 1; p=0.0002, ANOVA). This was greater in higher pH (Fig. 1). Some enzymes in a
result shows that the activity in the fermentation of E. process of the fermentation require H + source
coli depends on pH values.
(Bragramyan and Trchounian, 2003). However, the