mutagenesis and/or site-directed mutagenesis [51]. Finally, exogenous enzymes,
such as fungal enzymes with high biodegradation capacity, can be recombinantly
expressed in microalgae. Microalgae have higher growth rates than fungi, minimal
growth requirements (phototrophy), and therefore potentially lower bioremediation
costs [52]. For example, Chiaiese et al. [53] succeeded in producing the fungal
laccase POX A1b in Chlamydomonas pitschmannii, Chlorella emersonii, and
Ankistrodesmus braunii for the remediation of phenolic compounds from olive oil
mill wastewaters. However, the genetic engineering of microalgae is in its infancy,
and numerous limitations such as low transformation efficiencies and low recombinant protein yields still need to be overcome [52]. In addition to the current
technology limitations, for many countries, legislation around the limited use, or
the total ban, of genetically modified organisms (GMO) due to the risks and potential
impact on the environment means that, at present, genetically modifying microalgae
for NSAID biodegradation is not a viable option.
Microalgae play a role in enhancing bacterial biodegradation of NSAIDs. In
microalgae-bacteria coupled treatment systems, microalgal photosynthesis provides
the necessary oxygen, a key electron acceptor, for aerobic bacterial degradation of
the organic compounds, while microalgal released dissolved organic matter (DOM)
provides the necessary substrates for bacterial co-metabolism of compounds such as
NSAIDs [2]. For example, Matamoros et al. [54] successfully demonstrated
microalgal enhancement of bacterial biodegradation of the NSAID ibuprofen. The
authors found that, in the presence of microalgae, bacterial degradation of ibuprofen
increased from 15 to 60%, following 3 days of incubation under laboratory conditions [54]. However, the exact mechanism for microalgal enhancement of bacterial
degradation of NSAIDs and other organic compounds is not fully understood.
Investigations into the interactions between the two organisms and conditions that
further enhance coupled degradation would help to enable the development of
biological-mediated NSAID remediation.
Microalgae may also enhance the photodegradation of NSAIDs through the
release of DOM, which is comprised of a range of molecules such as hydrophilic
organic acids, hemicellulose, humic acids, and fulvic acids. This released DOM is
thought to enhance photodegradation through various mechanisms, including catabolic processes, redox cycling, production of hydroxyl radicals, or inhibiting photooxidation by competitive reaction with radicals, resulting in the photosensitized
transformation of NSAIDs [55]. Photodegradation of the NSAIDs diclofenac [54,
56] and ibuprofen [54] in the presence of microalgal-derived DOMs has been
successfully demonstrated in both wastewater treatment high rate algal ponds and
photobioreactors, with reported removal rates between 82 and 99% compared to 7%
for biodegradation.
Options for cost-effective microalgal degradation of NSAIDs are limited due to
the hydrophilic nature of the compounds and the negatively charged cell surface of
the microalgae. The most promising options include coupled microalgal-bacterial
Contemporary Methods for Removal of Nonsteroidal Anti-inflammatory Drugs in. . .
225
such as fungal enzymes with high biodegradation capacity, can be recombinantly
expressed in microalgae. Microalgae have higher growth rates than fungi, minimal
growth requirements (phototrophy), and therefore potentially lower bioremediation
costs [52]. For example, Chiaiese et al. [53] succeeded in producing the fungal
laccase POX A1b in Chlamydomonas pitschmannii, Chlorella emersonii, and
Ankistrodesmus braunii for the remediation of phenolic compounds from olive oil
mill wastewaters. However, the genetic engineering of microalgae is in its infancy,
and numerous limitations such as low transformation efficiencies and low recombinant protein yields still need to be overcome [52]. In addition to the current
technology limitations, for many countries, legislation around the limited use, or
the total ban, of genetically modified organisms (GMO) due to the risks and potential
impact on the environment means that, at present, genetically modifying microalgae
for NSAID biodegradation is not a viable option.
Microalgae play a role in enhancing bacterial biodegradation of NSAIDs. In
microalgae-bacteria coupled treatment systems, microalgal photosynthesis provides
the necessary oxygen, a key electron acceptor, for aerobic bacterial degradation of
the organic compounds, while microalgal released dissolved organic matter (DOM)
provides the necessary substrates for bacterial co-metabolism of compounds such as
NSAIDs [2]. For example, Matamoros et al. [54] successfully demonstrated
microalgal enhancement of bacterial biodegradation of the NSAID ibuprofen. The
authors found that, in the presence of microalgae, bacterial degradation of ibuprofen
increased from 15 to 60%, following 3 days of incubation under laboratory conditions [54]. However, the exact mechanism for microalgal enhancement of bacterial
degradation of NSAIDs and other organic compounds is not fully understood.
Investigations into the interactions between the two organisms and conditions that
further enhance coupled degradation would help to enable the development of
biological-mediated NSAID remediation.
Microalgae may also enhance the photodegradation of NSAIDs through the
release of DOM, which is comprised of a range of molecules such as hydrophilic
organic acids, hemicellulose, humic acids, and fulvic acids. This released DOM is
thought to enhance photodegradation through various mechanisms, including catabolic processes, redox cycling, production of hydroxyl radicals, or inhibiting photooxidation by competitive reaction with radicals, resulting in the photosensitized
transformation of NSAIDs [55]. Photodegradation of the NSAIDs diclofenac [54,
56] and ibuprofen [54] in the presence of microalgal-derived DOMs has been
successfully demonstrated in both wastewater treatment high rate algal ponds and
photobioreactors, with reported removal rates between 82 and 99% compared to 7%
for biodegradation.
Options for cost-effective microalgal degradation of NSAIDs are limited due to
the hydrophilic nature of the compounds and the negatively charged cell surface of
the microalgae. The most promising options include coupled microalgal-bacterial
Contemporary Methods for Removal of Nonsteroidal Anti-inflammatory Drugs in. . .
225