de-polymerization of lignin into building blocks and designing microbial biosynthetic pathway of recalcitrant lignin forms can manage lignocellulosic compounds.
The fundamental principle of bioremediation is that microorganisms are able to
generate energy for their growth and productivity by degrading hazardous
contaminants. Besides spontaneous bioremediation, there is a need for conscious
in situ release of engineered or tailor-designed microbiota to degrade organics and
convert heavy metal(oid)s into less toxic forms (Ravikumar et al. 2017). Microbial
whole-cell biosensors produce a quantifiable real-time signal (growth characteristics,
enzymatic activity) enabling detection and quantification of chemical effluents in
soil (Lagarde and Jaffrezic-Renault 2011; Aracic et al. 2015). SynBio development
has allowed a reporter gene to be placed under the regulation of a promoter that is
transcriptionally active in the incidence of an explicit pollutant. CSIRO presented a
very interesting example where engineered microorganisms can act as biosensors to
timely detect contaminants in soil or feedstock. CSIRO constructed CYBERNOSE®
sensor by implanting a protein replicating the smell receptors of the nematode into
yeast or bacteria. In the presence of toxins or contaminants in food, CYBERNOSE
changes shape and emits a mixture of blue and green light indicating the binding of
the certain foreign molecule, thus providing food safety (Vickers 2016). SynBio
strategy can even assemble the necessary genetic circuits which not only perform
real-time scrutiny of the exogenous toxin but can also trim down its level. These
synthetic genetic circuits can be assembled using a two-component regulatory
system (TCRS) in bacteria (Casino et al. 2010). TCRSs identifying organic
compounds (benzene, toluene, ethylbenzene, biphenyl, styrene, fumarate and
malate) also regulate the gene expression of catabolic enzymes for these compounds
and subsequently the breakdown product can be a carbon resource for microorganism (Tropel and Van Der Meer 2004). However, Ravikumar et al. (2017) advised
that the engineered bacterial system should modulate bacterial genes only in the
presence of the target in the environment. In today’s era, numerous genetic switches
(assembled using transcriptional repressors or activators) are accessible to turn on
gene expression once an exogenous toxin has reached its activation threshold. Few
switches developed to control the cellular responses are (1) inverter switches producing a reciprocal output (Yokobayashi et al. 2002); (2) biphasic switches using
both negative and positive regulation and responding to even minimal inputs (Isaacs
et al. 2003); (3) toggle switches using two repressors that cross-regulate each other’s
promoters (Gardner et al. 2000); and (4) riboswitches regulating gene expression by
inhibiting protein synthesis (Mandal and Breaker 2004). Similarly, many logic gate
types have been developed for biological circuits, including ‘NAND’, ‘NOT IF’ and
‘NOR’ (Guet et al. 2002). The incorporation of nanomaterials (gold particles,
magnetic beads and carbon nanotubes) and electron mediators in electrochemical
biosensors can improve the detection range of numerous water contaminants
(Lagarde and Jaffrezic-Renault 2011). For example, the arrest of electroactive
Pseudomonas putida cells on electrodes using carbon nanotubes resulted in an
80-fold augment in sensing accuracy and 2.8-fold rise in reaction time to trichloroethylene (Hnaien et al. 2011). Cyanobacteria strains have been engineered as in situ
bioindicators of ecotoxicity, N, P and metal(oid)s concentration using luciferase in a
15 Plant Synthetic Biology: A Paradigm Shift Targeting Stress Mitigation,. . .
455
The fundamental principle of bioremediation is that microorganisms are able to
generate energy for their growth and productivity by degrading hazardous
contaminants. Besides spontaneous bioremediation, there is a need for conscious
in situ release of engineered or tailor-designed microbiota to degrade organics and
convert heavy metal(oid)s into less toxic forms (Ravikumar et al. 2017). Microbial
whole-cell biosensors produce a quantifiable real-time signal (growth characteristics,
enzymatic activity) enabling detection and quantification of chemical effluents in
soil (Lagarde and Jaffrezic-Renault 2011; Aracic et al. 2015). SynBio development
has allowed a reporter gene to be placed under the regulation of a promoter that is
transcriptionally active in the incidence of an explicit pollutant. CSIRO presented a
very interesting example where engineered microorganisms can act as biosensors to
timely detect contaminants in soil or feedstock. CSIRO constructed CYBERNOSE®
sensor by implanting a protein replicating the smell receptors of the nematode into
yeast or bacteria. In the presence of toxins or contaminants in food, CYBERNOSE
changes shape and emits a mixture of blue and green light indicating the binding of
the certain foreign molecule, thus providing food safety (Vickers 2016). SynBio
strategy can even assemble the necessary genetic circuits which not only perform
real-time scrutiny of the exogenous toxin but can also trim down its level. These
synthetic genetic circuits can be assembled using a two-component regulatory
system (TCRS) in bacteria (Casino et al. 2010). TCRSs identifying organic
compounds (benzene, toluene, ethylbenzene, biphenyl, styrene, fumarate and
malate) also regulate the gene expression of catabolic enzymes for these compounds
and subsequently the breakdown product can be a carbon resource for microorganism (Tropel and Van Der Meer 2004). However, Ravikumar et al. (2017) advised
that the engineered bacterial system should modulate bacterial genes only in the
presence of the target in the environment. In today’s era, numerous genetic switches
(assembled using transcriptional repressors or activators) are accessible to turn on
gene expression once an exogenous toxin has reached its activation threshold. Few
switches developed to control the cellular responses are (1) inverter switches producing a reciprocal output (Yokobayashi et al. 2002); (2) biphasic switches using
both negative and positive regulation and responding to even minimal inputs (Isaacs
et al. 2003); (3) toggle switches using two repressors that cross-regulate each other’s
promoters (Gardner et al. 2000); and (4) riboswitches regulating gene expression by
inhibiting protein synthesis (Mandal and Breaker 2004). Similarly, many logic gate
types have been developed for biological circuits, including ‘NAND’, ‘NOT IF’ and
‘NOR’ (Guet et al. 2002). The incorporation of nanomaterials (gold particles,
magnetic beads and carbon nanotubes) and electron mediators in electrochemical
biosensors can improve the detection range of numerous water contaminants
(Lagarde and Jaffrezic-Renault 2011). For example, the arrest of electroactive
Pseudomonas putida cells on electrodes using carbon nanotubes resulted in an
80-fold augment in sensing accuracy and 2.8-fold rise in reaction time to trichloroethylene (Hnaien et al. 2011). Cyanobacteria strains have been engineered as in situ
bioindicators of ecotoxicity, N, P and metal(oid)s concentration using luciferase in a
15 Plant Synthetic Biology: A Paradigm Shift Targeting Stress Mitigation,. . .
455