Microbially Derived Off-Flavor from Geosmin and 2-Methylisoborneol: Sources and Remediation - Reviews of Environmental Contamination and Toxicology - page 15

catabolic plasmids or the genomic DNA. Horizontal transfer of genes among bacteria
has a major impact on the adaptability of bacteria during changing environmental
conditions (Trevors et al. 1987). Gene bioaugmentation is the process of obtaining
enhanced activity after gene transfer from an introduced donor organism into a
member of the indigenous microbial environment (Pepper et al. 2002). This process
has the potential to become a powerful tool in environmental management
(DiGiovanni et al. 1996; Chen and Wilson 1997; Grommen and Verstraete 2002;
Debashish et al. 2005).
To date, investigations related to bioremediation of geosmin and MIB are lim-
ited. Both are major causes of concern because they are difficult to remove by con-
ventional water treatment methods (Lalezary et al. 1986). Biodegradation could be
an alternative remediation technique, which needs to be investigated. Izaguirre et
al. (1988) isolated mixed bacterial populations that biodegrade MIB slowly at ppb
levels, whereas the related naturally occurring compound isoborneol was degraded
rapidly, even at ppm levels, which may be attributed to the absence of the methyl
group at carbon 2 in isoborneol and its presence in MIB, which might exert steric
hindrance of the hydroxyl group (Medsker et al. 1969; Trudgill 1984).
Saadoun (2005) studied the ability of Pseudomonas sp. isolated from different
soils contaminated with fuel spills to degrade MIB. The Pseudomonas group, espe-
cially P. aeruginosa , is common in freshwater and sediments (Hoadley 1968; Pellett
et al. 1983) and well known for its metabolic versatility resulting from utilization of
a wide range of substrates (Stainer et al. 1966). However, it has been reported that
natural strains of this species do not have plasmids that encode degradative genes
(Haas 1983). Walker and Higginbotham (2000) isolated an aquatic bacterium from
pond water that could be a potential microbial algicide to lyse cells of some selected
cyanobacteria, including species of Anabaena and Oscillatoria . Studies conducted
by Klausen et al. (2005) showed that indigenous stream bacteria were capable of
reducing the odors caused by geosmin and MIB produced by Streptomyces , and that
enrichment with Luria-Bertani medium stimulated the degradation.
Lauderdale et al. (2004) isolated and characterized a bacterium implicated in
aerobic degradation of MIB. Its 16S-rRNA phylogenetic analysis revealed that it is
more closely related to Bacillus fusiformis and Bacillus sphaericus . Westerhoff
et al. (2005) observed a magnitude change in MIB concentrations caused by ther-
mal destratification of the reservoirs and concluded that biodegradation appeared
more important than volatilization, photolysis, or adsorption. Saadoun (2005)
modified the method of Jacobs et al. (1983) to determine the ability of different
Pseudomonas sp. to degrade MIB-like compounds by transforming them to alcohol,
detection of which would be an applicable approach for detecting the activity of
microorganisms on this volatile compound.
Saadoun and El-Migdadi (1998) suggested that naturally occurring geosmin
produced by Streptomyces halstedii could be degraded by specific species of
gram-positive bacteria. They applied the technique of detection of alcohol produc-
tion as a result of odorous compound oxidation for the screening of bacteria that
degrade geosmin-like compounds. Hoefel et al. (2006) reported the cooperative
degradation of geosmin by a consortium comprising three gram-negative bacteria
isolated from a biologically active sand filter column, similar to cultured species