102
G. Grasso et al.
variable fragment against the explosive TNT. This approach could be interesting for
the development of future multi-functional sensing platforms (Ford et al. 2016).
4.2.3 Nanocellulose
The genetic engineering tool set has recently offered new perspectives also for the
production of modified bacterial nanocellulose with improved features. Jacek et al.
(2019b) have described the impact of motA, motB genes overexpression both on
bacterial nanocellulose structure and production yield in K. hansenii ATCC 23769.
More specifically, the analysis of two mutant phenotype motA+ and motB+ overexpressing motA, motB genes has revealed changes in cellular elongation, a threefold
increase in speeding motility of mutant colonies and a 6% and 20% higher production
yield, respectively, compared to the wild type K. hansenii ATCC 23769. Moreover,
motA+ and motB+ overexpressing mutants have produced bacterial nanocellulose
membranes with pores almost nine times larger and about two time thicker fibers.
Although other studies will be required, these results suggested that the controlling of K. hansenii motility and cell size might tune the production of well-defined
three-dimensional bacterial nanocellulose scaffolds (Jacek et al. 2019b).
Through repeated static cultures, Taweecheep et al. (2019) have obtained four
bacterial nanocellulose-producing revertant strains from a bcsC loss-of-function
mutant Komagataeibacter oboediens MSKU 3 E3. The revertant strains produced
bacterial nanocellulose with different production yield and dimension. In particular, the R30-3 revertant strain produced the highest amount of bacterial nanocellulose (2.15 g dry weight l
−1 ) and the R37-9 revertant strain produced a bacterial
nanocellulose with an exceptionally small average diameter of 34.58 nm and relatively homogeneous fine fibrils with a narrower range of width distribution (about 20
to 60 nm). The genome analysis of R37-9 revertant strain has revealed a one amino
acid substitution in the bcsCI gene, the N713D mutation (Taweecheep et al. 2019).
4.2.4 Nanowires
Genetic engineering has proved to be useful also for functional and structural modification in bacteria nanowires. Tan et al. (2016) reported genetically engineered model
microorganism G. sulfurreducens a 2000-fold increase in electrical conductivity and
diameter of nanowires filaments has been reduced by half to 1.5 nm. In this case,
genetic modification effected the modification of aminoacidic composition of the
carboxyl end of PilA protein, the structural component of bacterial nanowires (Tan
et al. 2016). In a later paper, Tan et al. (2017) performed the heterologous expression
of the pilA gene of G. metallireducens GS15 in G. sulfurreducens MP. The individual
pili prepared at physiologically relevant pH 7 showed a conductivity 5000-fold higher
than the conductivity of G. sulfurreducens pili at pH 7 and nearly 1 million-fold
higher than the conductivity of G. uraniireducens pili at the same pH. The functionalization of electrically conductive protein nanowires in G. sulfurreducens strain
G. Grasso et al.
variable fragment against the explosive TNT. This approach could be interesting for
the development of future multi-functional sensing platforms (Ford et al. 2016).
4.2.3 Nanocellulose
The genetic engineering tool set has recently offered new perspectives also for the
production of modified bacterial nanocellulose with improved features. Jacek et al.
(2019b) have described the impact of motA, motB genes overexpression both on
bacterial nanocellulose structure and production yield in K. hansenii ATCC 23769.
More specifically, the analysis of two mutant phenotype motA+ and motB+ overexpressing motA, motB genes has revealed changes in cellular elongation, a threefold
increase in speeding motility of mutant colonies and a 6% and 20% higher production
yield, respectively, compared to the wild type K. hansenii ATCC 23769. Moreover,
motA+ and motB+ overexpressing mutants have produced bacterial nanocellulose
membranes with pores almost nine times larger and about two time thicker fibers.
Although other studies will be required, these results suggested that the controlling of K. hansenii motility and cell size might tune the production of well-defined
three-dimensional bacterial nanocellulose scaffolds (Jacek et al. 2019b).
Through repeated static cultures, Taweecheep et al. (2019) have obtained four
bacterial nanocellulose-producing revertant strains from a bcsC loss-of-function
mutant Komagataeibacter oboediens MSKU 3 E3. The revertant strains produced
bacterial nanocellulose with different production yield and dimension. In particular, the R30-3 revertant strain produced the highest amount of bacterial nanocellulose (2.15 g dry weight l
−1 ) and the R37-9 revertant strain produced a bacterial
nanocellulose with an exceptionally small average diameter of 34.58 nm and relatively homogeneous fine fibrils with a narrower range of width distribution (about 20
to 60 nm). The genome analysis of R37-9 revertant strain has revealed a one amino
acid substitution in the bcsCI gene, the N713D mutation (Taweecheep et al. 2019).
4.2.4 Nanowires
Genetic engineering has proved to be useful also for functional and structural modification in bacteria nanowires. Tan et al. (2016) reported genetically engineered model
microorganism G. sulfurreducens a 2000-fold increase in electrical conductivity and
diameter of nanowires filaments has been reduced by half to 1.5 nm. In this case,
genetic modification effected the modification of aminoacidic composition of the
carboxyl end of PilA protein, the structural component of bacterial nanowires (Tan
et al. 2016). In a later paper, Tan et al. (2017) performed the heterologous expression
of the pilA gene of G. metallireducens GS15 in G. sulfurreducens MP. The individual
pili prepared at physiologically relevant pH 7 showed a conductivity 5000-fold higher
than the conductivity of G. sulfurreducens pili at pH 7 and nearly 1 million-fold
higher than the conductivity of G. uraniireducens pili at the same pH. The functionalization of electrically conductive protein nanowires in G. sulfurreducens strain