Artificial Spores - Cell Surface Engineering: Fabrication of Functional Nanoshells - page 149

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Figure 8.3 Passive control of cell division via a non-LbL approach. (a) Individual

yeast cells were nanoencapsulated with polydopamine shells, and their
division was controlled by the shell thickness. (b) Silica shells were
formed on the yeast cell surfaces by bioinspired silicification, which
prolonged the lag phase to some extent compared with the native yeast.
Reproduced with permission from the American Chemical Society
(Copyright 2011) 14 and Wiley (Copyright 2009). 15

An alternative method for delaying cell division is to use inorganic ma-
terials in the encapsulation process. The formation of hierarchically organ-
ized inorganic structures occurs in Nature, where catalytic peptides/proteins
harmonize with inorganic precursors under physiological conditions. The
bioinspired approach, which utilizes the mechanistic chemical principles of
biomineralization processes, is more attractive than conventional chemical
methods for preserving the original viability of living cells, because bioin-
spired mineralization occurs under physiologically mild conditions.
The siliceous cell walls of diatoms offer one chemical approach for the
construction of artificial spores that is cytocompatible and generates the
robust shells that can control the cell division. 23 Individual living yeast cells
were encapsulated within silica shells, inspired by the silicification of
diatoms. 15 The encapsulation process was achieved in two sequential bio-
compatible steps: LbL self-assembly and bioinspired silicification. Because
quaternary amine groups are reported to be a catalytic template for bioin-
spired silicification, 24 poly(diallyldimethylammonium chloride) was chosen
as one of the PEM components. After bioinspired silicification, 50-nm thick
silica shells were formed on the yeast-cell surfaces. The resultant cell-in-
nanoshell structures persisted in their ''dormant'' state and did not divide
for 20 h (Figure 8.3b).
Although the examples cited emulate the basic features of natural endo-
spores, their processes are predominantly passive, simply delaying or re-
tarding cell division relative to that of native cells. However, natural
endospores always sense their surrounding environments and degrade their
shells when conditions are appropriate for their reproduction. Therefore, the
advanced features of artificial spores exert temporal control over cell division
in response to external signals.

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