Biology Reference
In-Depth Information
contained in the organism. The following sections review the techniques
that have been developed using each of the cellular macromolecules as
their basis.
8.2.1. Fatty acids
Qualitatively and quantitatively, fatty acid composition in bacteria is
highly conserved and quite stable if culture conditions are highly stan-
dardized. The use of fatty acids as a taxonomic tool has been discussed
for almost 50 years and has been successfully applied to various taxa for
over 20 years.
16
Differences in fatty acid chain lengths, positions of double
bonds, and binding of functional groups potentially make them useful for
identification purposes.
Whole cell fatty acid methyl ester (FAME) analysis can be carried out
by gas chromatography. Lipski et al.
17
analyzed the fatty acid profiles of
nitrite-oxidizing species and found that each of the genera,
Nitrobacter
,
Nitrococcus
,
Nitrospina
, and
Nitrospira
had a distinct profile. Furthermore,
specific fatty acids could be assigned to particular species; for example,
11-methyl-hexadecanoic acid was detected only in
Nitrospria moscoviensis
and can be used as potential lipid marker for detection of this species in
environmental and enrichment samples. Cluster analysis of the fatty acid
profiles for the organism were in accordance with 16S rRNA sequence-
based phylogeny for the nitrite-oxidizing bacteria.
17
FAME analysis has also been used to identify and quantify individual
fatty acids that are useful to assess the relative differences and similarities
among and between microbial communities from groundwater.
18
Figure
8.1
shows the gas chromatograph results obtained from one groundwater
well on two different occasions. Changes in the profile are attributed to dif-
ferences in the composition of the communities.
The main advantage of FAME analysis is that it is cheap, easy, and can be
automated. However, most of the studies to date have used fatty acid to gen-
erate community profiles and monitor changes in community structure over
time or space and not to detect individual strains in samples. Parveen et al.
19
found that FAME was not sensitive enough to differentiate between
E. coli
from human and nonhuman sources. Using fatty acid isopropyl ester analysis,
which has a simpler protocol than FAME, microbial community structure was
monitored in an activated sludge secondary wastewater treatment system.
20
Werker et al.
20
found that the method allowed for the generation of meaning-
ful and quantitative data for changes in activated sludge quality but could not
be directly compared to FAME profiles without a correction factor.
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