Biology Reference
In-Depth Information
nonlytic M13 bacteriophage to express lex A3, a repressor of the SOS response network that
protects bacteria against DNA damage induced by antibiotics. Subsequent exposure of
various resistant bacterial strains to this genetically engineered bacteriophage in the presence
of three major classes of antibiotics (quinolones, ß-lactams, and aminoglycosides) resulted
in up to a 500-fold enhancement in bacterial cell death, compared with treatment by
antibiotics alone.
Another major challenge faced in combating bacterial infections is the formation of
protective biofilms by pathogenic bacteria,
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which shield them from antibiotics and
the host immune system. In another study by Lu et al.,
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the lytic T7 phage was genetically
engineered to express the enzyme dispersin B, which readily degrades the biofilm matrix.
Degradation of the biofilm matrix by dispersin B allowed exposure of unprotected bacterial
cells to infection and subsequent lysis by the genetically engineered T7 phage.
Naturally occurring commensal and symbiotic bacterial species within the human body can
be genetically engineered to prevent and fight infectious pathogens. Of particular interest is
E. coli
, which is probably the most abundant microbe found within the human body. Duan
and March
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genetically engineered
E. coli
to express both cholera autoinducer-1 (CAI-1)
and autoinducer-2 (CAI-2), both of which are naturally utilized by
Vibrio cholerae
for
quorum sensing. When the population density of
Vibrio cholerae
is high, elevated levels of
CAI-1 and CAI-2 secreted by the bacterial cells inhibit the secretion of the cholera toxin.
Hence, in this manner, the genetically engineered
E. coli
that produce CAI-1 and CAI-2 can
mitigate the virulence of
Vibrio cholerae
infections through the inhibition of cholera toxin
production. Rao et al.
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genetically engineered a highly colonizing probiotic strain of
E. coli
(Nissle 1917) to secrete HIV-gp41-hemolysin A hybrid peptides that block HIV fusion and
subsequent entry into target cells. Subsequently, it was demonstrated that the genetically
engineered
E. coli
was capable of colonizing various tissues such as the rectum, vagina, and
small intestine of mice for prolonged durations up to several months, while actively
secreting the HIV fusion inhibitor peptide.
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Besides targeting infectious pathogens per se, it may also be possible to take a synthetic
biology approach to target their insect vectors. Windbichler et al.
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attempted to reduce the
ability of mosquitoes to transmit malaria by disrupting the genes that encode malaria vector
capability within the mosquito genome. This was achieved with a synthetic gene drive
comprised of the homing endonuclease gene I-SceI together with aberrant mosquito
regulatory genes that reduced malaria vector capability. The homing endonuclease induced
double-stranded DNA breaks, which in turn activated the endogenous DNA repair system
within the mosquito cells. The homologous chromosome containing the synthetic gene
drive was utilized as a template for repair, which in turn caused both of the chromosomes
to carry the synthetic gene drive. In this manner, the synthetic gene drive that reduced
malaria vector capability could be transmitted rapidly within mosquito populations.
Vaccine development could also benefit from a synthetic biology approach. Amidi et al.
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were able to encapsulate a reconstituted bacterial transcription and translation network,
together with DNA encoding a model antigen within synthetic liposome vesicles, and utilize
these to provoke a humoral immune response in mice. This can provide a safer alternative
to attenuated live antigens without the potential of becoming virulent.
In another study by Coleman et al.,
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an attenuated poliovirus vaccine was created by
exploiting species-specific codon bias. This is based on the principle that while several
different codon sequences can code for the same amino acid, each individual species
exhibits bias for the adjacent codons that it can translate efficiently into protein. Hence, by
switching synonymous codons that encoded the poliovirus capsid protein, the translation
efficiency was greatly reduced, resulting in an attenuated poliovirus with reduced virulence
that could be utilized as a live vaccine.
