Volume 6, Spring 2008 - Saddleback College

37
Saddleback Journal of Biology
Spring 2008
Fall 2007 Biology 3A Abstracts
efficiently with the energy by using mixed acid
fermentation. According to the studies of Bragramyan
and Trchounian (2003), oxidation of glucose in
bacteria involves a chain of sequential chemical
reactions with some enzymes and H+ and CO 2 in
mixed-acid fermentation of E. coli.
In this study, Escherichia coli will be used
because it is closely related to our lives and has many
advantageous characteristics as a production host, such
as rapid growth under aerobic and anaerobic conditions
and simple nutritional requirements (Chang et al.,
1999). E. coli live in mammals’ gastrointestinal under
anaerobic condition and also have to be able to survive
in the low of the gastric stomach to colonize the
intestinal tract of humans if they are injected from
mouth (Diez-Gonzalez et al., 1998). Thus, there are
the important relationships between pH and E. coli
fermentation.
The previous study shows that increasing the
pH at the interval of 0.5 resulted in an increase in
cumulative volume of gas production up to pH 6 and
thereafter the production dropped (Chittibabu et. al.,
2006). In the same study, the poor hydrogen
production at low pH, lower than 5.5 could be due to
the increased formation of acidic metabolites, which
destroys the cell's ability to maintain internal pH
(Chittibabu et. al., 2006). However, this study was
demonstrated from pH 5 to pH 7, and it does not show
the effects of various pH values on the gas production
of E. coli. Therefore, the effects of various pH groups
on E. coli fermentation will be tested (pH 1, 3, 5, 7, and
9) in this study, and the volume of gas produced in
fermentation tubes will be measured. The hypothesis
being tested is that gas production during E. coli
fermentation under different pH conditions will be
significantly different.
Materials and Methods
Materials and medium
Escherichia coli used in this study were
provided from Biological Department at Saddleback
College. For the medium for Escherichia coli, 1% of
glucose solution was prepared by using five 100-mL
volumetric flasks. Glucose was used for the important
sugar source for the fermentation of E. coli (Xu et al.,
1999). Each glucose solution was adjusted to be
appropriate pH value (pH 1, 3, 5, 7, 9) with 1.0 M HCl
or 1 % NaOH. The pH values were checked with pHindicator
strips (range 0-14 and 0-6) (Gibbstown, NJ,
USA).
Fermentation conditions and measurement
Five fermentation tubes were used for each pH,
and 25 fermentation tubes were filled with 14.5 mls of
glucose solution and 0.5 mls of E. coli solution without
any bubbles inside. Anaerobic condition was made by
using fermentation tubes. Aseptic technique was
performed in each time of transfer of E. coli to
fermentation tubes. For the fermentation tubes, a 10-
mL graduated cylinder was used while 0.5 mls of E.
coli solution were measured by using a micropipette.
The fermentation tubes were put in the incubator at 36
ºC for 48 hours. The volume of gas production in the
fermentation was measured after 24 and 48 hours. The
amount of gas produced in each tube was indicated by
a scale in milliliter.
Statistical analysis
Data were analyzed, using Microsoft Excel
2003 (Microsoft, Redmond, WA) with ANOVA to
determine if there were significant differences between
pH groups. The difference was considered significant
at P < 0.05 for Bonferroni Correction. All data
reported were means ± SE unless noted otherwise.
Results
Gas Production
Gas production in the fermentation of E. coli
significantly differs between different pH groups
(p=0.0002