Exploiting Photosynthesis for Biofuel Production - Biophotonics - page 27

centre II- and thus reduce sensitivity) is explained by the observation that
antenna proteins (named Lhc) are not only involved in light harvesting but
also have a major role in photoprotection [16]. As a consequence, the deletion
of all antenna proteins reduces the capacity for photoprotection to a level
making insignificant the advantage obtained in terms of light distribution.
However, among Lhc polypeptides, individual members proteins are spe-
cialized in light harvesting, while others in photoprotection [17]. Thus, to
obtain mutants optimized to bioreactor conditions, the first step consists in
identifying members of Chlamydomonas Lhc protein family essential for pho-
toprotection vs. those that can be deleted to lower the optical density.
To this aim, we apply two different approaches: in vivo approach consists
in the creation of a library of Chlamydomonas insertional mutants. In these
mutants genes are randomly knocked out by the insertion of a resistance
cassette. These mutants are screened for a smaller antenna size, by analyzing
their fluorescence yield properties and Chl a/b ratio. Strains with a reduced
antenna content, in fact, would have lower cell fluorescence yield and higher
Chl a/b ratio, as Chl b is specifically bound to Lhc proteins.
An in vitro approach is complementary: individual members of Lhc fam-
ily are studied one by one. Each Lhc protein identified in the genome [18]
is characterized by expressing in bacteria the corresponding polypeptides
and refolded in vitro to obtain the native pigment protein complex. By this
method, each protein will be characterized individually for its capacity of light
harvesting and photoprotection.
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