2. Fatty Acids as Trophic and Chemical Markers
31
also used to estimate the proportion of bacteria present in the POM at different
depths of Ace Lake and indicated a near-tenfold increase in bacterial biomass
from surface to the depth of 23 m (Mancuso et aI., 1990). Comparable results were
obtained in a study of lipid markers in POM of a coastal brackish pond near Cape
Cod (Wakeham and Canuel, 1990). This study showed that fatty acids of photoeucaryotes (e.g., CI6 PUFA, 18:30)3, and 18:40)3) were abundant in the oxic
surface waters, whereas bacterial fatty acids (18: 1 0)7 and anteiso 15:0) dominated
the deepest anoxic zone and the water-sediment interface. These differences
between surface and deeper waters were accentuated during the stratification of
the pond in late summer, when anaerobic processes increased, favoring the production of bacterial fatty acids (especially 18: I 0)7) in the metalimnion and
hypolimnion.
Animal lipids may present large concentrations of PUFA that are derived from
autotrophic sources such as 18:30)3, 20:50)3, and 22:60)3 but may also contain
minor amounts of branched and odd-numbered saturated fatty acids of bacterial
origin. For example, the proportions of these branched and odd-numbered fatty
acids in the triacylglycerols of zooplankton are good indicators of the relative
importance of algae and bacterial biomass as alternative sources of food for filter
feeders (DesviJettes et aI., 1994). Considering that all animals normally host a
population of microbes of one type or another in their digestive systems, the
occurrence of bacterial fatty acids in their lipids should not be considered rare.
Small quantities of bacterial fatty acid markers in animal fats and oils likely
represent the degree of detail and the quality of a particular analysis. For example,
the lipids of the mummichog fish (Fundulus heteroclitus) contain small proportions of cyclopropanoid (cis-9,l0-methylenehexadecanoic and cis-9,1O-methyleneoctadecanoic acids) and iso, anteiso, and branched fatty acids characteristic of
bacteria (Cosper et aI., 1984). Results of field and laboratory experiments indicated that the bacterial fatty acids found in the tissues of F heteroclitus originated
from both dietary sources and from the metabolism of commensal bacteria in the
fish intestine (Cosper et aI., 1984).
It has been reported that the lipids of beavers contained up to 3% of the total
fatty acids as trans-I 1-18:1 and a conjugated diunsaturated cis-9, trans-I 1-18:2
(Kakela and Hyvarinen, 1996; Kakela et aI., 1996). These fatty acids are not
common constituents of the lipids of most vertebrates or of the beaver's diet
(Scholz and Boon, 1993), but they are normally found in the adipose tissue of
ruminants. The presence of substantial amounts of these bacterial fatty acids in the
lipids of beavers (particularly in the digestive tract) suggested that they originated
from microbes that hydrogenate dietary 18:20)6 in the beaver's intestine (Christie,
1981 ).
2.4.5. Fatty Acid Markers from Allochthonous Sources
Freshwater environments contain organic matter derived from a number of autochthonous and allochthonous sources, including algae, vascular plants, and decaying plant and animal materials. Lipids from these different sources can have
31
also used to estimate the proportion of bacteria present in the POM at different
depths of Ace Lake and indicated a near-tenfold increase in bacterial biomass
from surface to the depth of 23 m (Mancuso et aI., 1990). Comparable results were
obtained in a study of lipid markers in POM of a coastal brackish pond near Cape
Cod (Wakeham and Canuel, 1990). This study showed that fatty acids of photoeucaryotes (e.g., CI6 PUFA, 18:30)3, and 18:40)3) were abundant in the oxic
surface waters, whereas bacterial fatty acids (18: 1 0)7 and anteiso 15:0) dominated
the deepest anoxic zone and the water-sediment interface. These differences
between surface and deeper waters were accentuated during the stratification of
the pond in late summer, when anaerobic processes increased, favoring the production of bacterial fatty acids (especially 18: I 0)7) in the metalimnion and
hypolimnion.
Animal lipids may present large concentrations of PUFA that are derived from
autotrophic sources such as 18:30)3, 20:50)3, and 22:60)3 but may also contain
minor amounts of branched and odd-numbered saturated fatty acids of bacterial
origin. For example, the proportions of these branched and odd-numbered fatty
acids in the triacylglycerols of zooplankton are good indicators of the relative
importance of algae and bacterial biomass as alternative sources of food for filter
feeders (DesviJettes et aI., 1994). Considering that all animals normally host a
population of microbes of one type or another in their digestive systems, the
occurrence of bacterial fatty acids in their lipids should not be considered rare.
Small quantities of bacterial fatty acid markers in animal fats and oils likely
represent the degree of detail and the quality of a particular analysis. For example,
the lipids of the mummichog fish (Fundulus heteroclitus) contain small proportions of cyclopropanoid (cis-9,l0-methylenehexadecanoic and cis-9,1O-methyleneoctadecanoic acids) and iso, anteiso, and branched fatty acids characteristic of
bacteria (Cosper et aI., 1984). Results of field and laboratory experiments indicated that the bacterial fatty acids found in the tissues of F heteroclitus originated
from both dietary sources and from the metabolism of commensal bacteria in the
fish intestine (Cosper et aI., 1984).
It has been reported that the lipids of beavers contained up to 3% of the total
fatty acids as trans-I 1-18:1 and a conjugated diunsaturated cis-9, trans-I 1-18:2
(Kakela and Hyvarinen, 1996; Kakela et aI., 1996). These fatty acids are not
common constituents of the lipids of most vertebrates or of the beaver's diet
(Scholz and Boon, 1993), but they are normally found in the adipose tissue of
ruminants. The presence of substantial amounts of these bacterial fatty acids in the
lipids of beavers (particularly in the digestive tract) suggested that they originated
from microbes that hydrogenate dietary 18:20)6 in the beaver's intestine (Christie,
1981 ).
2.4.5. Fatty Acid Markers from Allochthonous Sources
Freshwater environments contain organic matter derived from a number of autochthonous and allochthonous sources, including algae, vascular plants, and decaying plant and animal materials. Lipids from these different sources can have