91
This work became a base for developing microbial biosensors for pollutant monitoring purposes. Most of the sensors developed till date fall under the taxonomic group
of microbes. This is due to rich analytical prospects of the microbes and their
reliability.
The development of sensor requires the immobilization of biorecognition element; it secures both the stabilization and proximity of the recognition element for
reuse. The immobilization plays a key role in developing stable biocomponent for
integration with transducers (Rodriguez-Mozaz et al. 2005). The immobilization
techniques are physical adsorption, cross-linkage, covalent binding, and entrapment
method. Selection of immobilization methods would depend on the nature of the
biomaterial and configuration of the transducer used. Cross-linkage and covalent
binding techniques are not suitable for microbial cells; it affects the viability and
may loss structural integrity, but applied for immobilization of antibodies/antigens
and the enzymes.
Natural polymers used for the entrapment of the cells include carrageenan, alginate, chitosan, and low-melting agarose. These polymers are known to be very useful in obtaining viable cell-immobilized systems. Among these, entrapment in
alginate by ionotropic gelation using a variety of divalent and trivalent cations has
found extensive use in immobilization (Gupte and D’Souza 1999). However, alginate and carrageenan have strong metal absorption capacities. There are many different types of microbial biocomponent (from disposable to reusable) by
immobilizing microbial cells on different supports and connected to transducers
(Kumar and D’Souza 2010, 2011; Jouanneau et al. 2012; Roda et al. 2011; Charrier
et al. 2010). Kumar and D’Souza (2010) reported an optical biosensor with immobilized bacteria Sphingomonas JK1 on the bottom side of the microplate and linked
with an optical plate. This system enables multiple sample detection on one plate.
Biosensor can detect 4–80 μM of methyl parathion and can be reused up to 75 times.
Jouanneau et al. (2012) reported an online biosensor analysis system for continuous monitoring of arsenic (As), cadmium (Cd), mercury (Hg), and copper (Cu) in
water by developing two bacterial biosensors, namely, Lumisens III and Lumisens
IV. In the first Lumisens, bioreporters were immobilized in agarose hydrogel in a
multiwall card, and in the second one, freeze-dried bacteria were utilized. The
Lumisens IV system was more successful in terms of stability, sensitivity, time consumption, and reproducibility (40%). Elad et al. (2011) reported a chip-based analysis system for continuous monitoring of heavy metals including arsenic and antimony
in water samples in laboratory conditions with a reproducibility of up to 20%.
4.5 Genetically Modified Biosensor
The genetically modified bacterial biosensor for specific pollutant appears to be easily achieved by various molecular techniques. Metabolic and protein engineering
has enhanced the production of biochemical signals. The genetically modified biosensor contains two genetic elements, namely, regulatory and reporter gene.
4 Genetically Modified Microbial Biosensor for Detection of Pollutants in Water…
This work became a base for developing microbial biosensors for pollutant monitoring purposes. Most of the sensors developed till date fall under the taxonomic group
of microbes. This is due to rich analytical prospects of the microbes and their
reliability.
The development of sensor requires the immobilization of biorecognition element; it secures both the stabilization and proximity of the recognition element for
reuse. The immobilization plays a key role in developing stable biocomponent for
integration with transducers (Rodriguez-Mozaz et al. 2005). The immobilization
techniques are physical adsorption, cross-linkage, covalent binding, and entrapment
method. Selection of immobilization methods would depend on the nature of the
biomaterial and configuration of the transducer used. Cross-linkage and covalent
binding techniques are not suitable for microbial cells; it affects the viability and
may loss structural integrity, but applied for immobilization of antibodies/antigens
and the enzymes.
Natural polymers used for the entrapment of the cells include carrageenan, alginate, chitosan, and low-melting agarose. These polymers are known to be very useful in obtaining viable cell-immobilized systems. Among these, entrapment in
alginate by ionotropic gelation using a variety of divalent and trivalent cations has
found extensive use in immobilization (Gupte and D’Souza 1999). However, alginate and carrageenan have strong metal absorption capacities. There are many different types of microbial biocomponent (from disposable to reusable) by
immobilizing microbial cells on different supports and connected to transducers
(Kumar and D’Souza 2010, 2011; Jouanneau et al. 2012; Roda et al. 2011; Charrier
et al. 2010). Kumar and D’Souza (2010) reported an optical biosensor with immobilized bacteria Sphingomonas JK1 on the bottom side of the microplate and linked
with an optical plate. This system enables multiple sample detection on one plate.
Biosensor can detect 4–80 μM of methyl parathion and can be reused up to 75 times.
Jouanneau et al. (2012) reported an online biosensor analysis system for continuous monitoring of arsenic (As), cadmium (Cd), mercury (Hg), and copper (Cu) in
water by developing two bacterial biosensors, namely, Lumisens III and Lumisens
IV. In the first Lumisens, bioreporters were immobilized in agarose hydrogel in a
multiwall card, and in the second one, freeze-dried bacteria were utilized. The
Lumisens IV system was more successful in terms of stability, sensitivity, time consumption, and reproducibility (40%). Elad et al. (2011) reported a chip-based analysis system for continuous monitoring of heavy metals including arsenic and antimony
in water samples in laboratory conditions with a reproducibility of up to 20%.
4.5 Genetically Modified Biosensor
The genetically modified bacterial biosensor for specific pollutant appears to be easily achieved by various molecular techniques. Metabolic and protein engineering
has enhanced the production of biochemical signals. The genetically modified biosensor contains two genetic elements, namely, regulatory and reporter gene.
4 Genetically Modified Microbial Biosensor for Detection of Pollutants in Water…