98
site. Biran et al. (2000) developed sensor system for monitoring the Cd in seawater
and soil samples. The Cd-stress responsive gene is fused to a lacZ gene and observed
the Cd concentrations in soil samples. Ivask et al. (2009) developed multiple number of recombinant bacterial biosensor for testing heavy metals and general toxicity.
In this study, they have used 19 recombinant bacterial strains representing various
group of gram-positive and gram-negative bacteria (Staphylococcus aureus, Bacillus
subtilis and E. coli, P. fluorescens, respectively) and were constructed to express the
luminescence gene (lux CDABE) as a response to heavy metals in water.
Tibazarwa et al. (2001) employed the luminescent bacterium Ralstonia eutropha
(AE2515) harbouring the lux gene to study bioavailable concentrations of nickel
(Ni) and cobalt (Co) in soil. This plasmid (pMOL1550) carried cnrYXH regulatory
genes that are transcriptionally fused to luxCDABE reporter system. Strain AE2515
was standardized for its specific responses to Co and Ni. The detection limits of the
biosensor were 0.1 μM for Ni and 9 μM for Co, respectively. Another study reported
the detection of As in water with 0.5–2.5 h incubation and detection limit recorder
as 7 mg/L (Trang et al. 2005). A recombinant Staphylococcus aureus strain was
developed for As analysis. The strain was found to be more stable (6 months), simple, and sensitive, and the detection limit reached up to7.5 mg/L (Tauriainen et al.
1999). Ravikumar et al. (2012) designed and applied biosensor for zinc (Zn) and
copper (Cu) in water samples. The P and cusC promoters were fused to a duallabelling reporter protein as an interactive biocomponent for zinc (Zn) and copper
(Cu) with the detectable limit of 16 μM and 26 μM for Zn and Cu, respectively, and
the sensor system proved sensitive and an effective technique for detection of Zn
2+
and Cu
2+
in field water samples.
Aleksic et al. (2007) reported biobrick sensor system (E. coli JM109/pSB1A2BBa- J33203) for As identification. The system was found to be a clear response to
arsenate concentrations as low as 5 ppb in environmental samples. Roointan et al.
(2015) developed a biosensor for the detection of Hg in liquid solutions. The sensor
carries gfp as a reporter gene under the control of Hg-inducible regulatory gene
from Pseudomonas pBS228 which was cloned into pUC19 vector and transferred
into Escherichia coli (E. coli) BL21 strain. The sensitivity of the sensor was evaluated with Hg metal. Modified biosensors respond to Hg (II), with detectable limit
reaching up to 10
−8
M for 3 h incubation. The E. coli DH5α strain harbouring the
luxAB reporter gene from Vibrio harveyi transcriptionally fused with arsR reported
gene (E. coli DH5 α (pJAMA-arsR)) for monitoring As in groundwater. The developed biosensor was also reported to have the presence of phosphate, silicate, and
iron and produces luminescence (Harms et al. 2005). To overcome this issue, recombinant DNA can help to enhance the specificity of microbial sensors by activating
specific pathways of metabolism and cellular uptake while switching off the undesirable’s gene action.
Wu et al. (2009) have improved the sensitivity of microbial biosensors via inserting additional repressor gene to reduce the background fluorescence by nonspecific
inducers such as isopropyl β-d-1-thiogalactopyranoside and increase the sensitivity
of the cells toward Cd. Another limitation which includes widespread use of microbial biosensors is the inherent difficulty of maintaining cell viability and activity in
S. Ganesan and N. Vasudevan
site. Biran et al. (2000) developed sensor system for monitoring the Cd in seawater
and soil samples. The Cd-stress responsive gene is fused to a lacZ gene and observed
the Cd concentrations in soil samples. Ivask et al. (2009) developed multiple number of recombinant bacterial biosensor for testing heavy metals and general toxicity.
In this study, they have used 19 recombinant bacterial strains representing various
group of gram-positive and gram-negative bacteria (Staphylococcus aureus, Bacillus
subtilis and E. coli, P. fluorescens, respectively) and were constructed to express the
luminescence gene (lux CDABE) as a response to heavy metals in water.
Tibazarwa et al. (2001) employed the luminescent bacterium Ralstonia eutropha
(AE2515) harbouring the lux gene to study bioavailable concentrations of nickel
(Ni) and cobalt (Co) in soil. This plasmid (pMOL1550) carried cnrYXH regulatory
genes that are transcriptionally fused to luxCDABE reporter system. Strain AE2515
was standardized for its specific responses to Co and Ni. The detection limits of the
biosensor were 0.1 μM for Ni and 9 μM for Co, respectively. Another study reported
the detection of As in water with 0.5–2.5 h incubation and detection limit recorder
as 7 mg/L (Trang et al. 2005). A recombinant Staphylococcus aureus strain was
developed for As analysis. The strain was found to be more stable (6 months), simple, and sensitive, and the detection limit reached up to7.5 mg/L (Tauriainen et al.
1999). Ravikumar et al. (2012) designed and applied biosensor for zinc (Zn) and
copper (Cu) in water samples. The P and cusC promoters were fused to a duallabelling reporter protein as an interactive biocomponent for zinc (Zn) and copper
(Cu) with the detectable limit of 16 μM and 26 μM for Zn and Cu, respectively, and
the sensor system proved sensitive and an effective technique for detection of Zn
2+
and Cu
2+
in field water samples.
Aleksic et al. (2007) reported biobrick sensor system (E. coli JM109/pSB1A2BBa- J33203) for As identification. The system was found to be a clear response to
arsenate concentrations as low as 5 ppb in environmental samples. Roointan et al.
(2015) developed a biosensor for the detection of Hg in liquid solutions. The sensor
carries gfp as a reporter gene under the control of Hg-inducible regulatory gene
from Pseudomonas pBS228 which was cloned into pUC19 vector and transferred
into Escherichia coli (E. coli) BL21 strain. The sensitivity of the sensor was evaluated with Hg metal. Modified biosensors respond to Hg (II), with detectable limit
reaching up to 10
−8
M for 3 h incubation. The E. coli DH5α strain harbouring the
luxAB reporter gene from Vibrio harveyi transcriptionally fused with arsR reported
gene (E. coli DH5 α (pJAMA-arsR)) for monitoring As in groundwater. The developed biosensor was also reported to have the presence of phosphate, silicate, and
iron and produces luminescence (Harms et al. 2005). To overcome this issue, recombinant DNA can help to enhance the specificity of microbial sensors by activating
specific pathways of metabolism and cellular uptake while switching off the undesirable’s gene action.
Wu et al. (2009) have improved the sensitivity of microbial biosensors via inserting additional repressor gene to reduce the background fluorescence by nonspecific
inducers such as isopropyl β-d-1-thiogalactopyranoside and increase the sensitivity
of the cells toward Cd. Another limitation which includes widespread use of microbial biosensors is the inherent difficulty of maintaining cell viability and activity in
S. Ganesan and N. Vasudevan