for several scientific and industrial applications [1]. Moreover, by reducing the need
for virgin raw materials and waste disposal, they have been the key for sustainable
industrial development along the fields of raw material processing like leather, pulp,
and paper production, up to more complex fields of detergent, textile, cosmetics,
and pharmaceuticals production [8, 9]. For the particular case of enzyme utilization
in environmental applications, this chapter will provide an overview of biological
systems that make use of photosynthetic microorganisms and their unique
enzyme-mediated metabolism for the treatment of wastewater, nutrient recovery,
and wastes valorization. A special focus will be given to the case studies of the
photo-enhanced biological phosphorus removal (photo–EBPR) and the phototrophic purple bacteria pond (PPBPond), which are, respectively, two innovative
technologies for phosphorous recovery and polyhydroxyalkanoates production in
illuminated open systems.
2 Diversity of Phototrophic Organisms: Overview
Phototrophy is a process that consists in converting light energy into a usable form
of chemical energy and it can be used by a great diversity of organisms, both
eukaryotic and prokaryotic. While all chlorophyll and/or bacteriochlorophyll containing phototrophs can synthetize ATP from light, one of the most differentiating
features between them regards their electron source and capability of producing
oxygen [10]. Microalgae and cyanobacteria are able to use water as the electron
source and thus, are capable of performing an oxygenic photosynthesis (i.e., oxygen
is produced) in a process that occurs in two distinct stages. The first stage includes
light-dependent reactions and takes place in specialized structures (chloroplasts)
where light energy is absorbed, driving the synthesis of ATP and NADPH in a
process coupled to the formation of oxygen from water (Fig. 1).
Photosystem II (PS II) produces a very strong oxidant (*+1250 mV) that is
capable of oxidizing water to molecular oxygen (+810 mV) [13]. Then, the electrons proceed via cytochrome bf complex to NADP
+ in photosystem I (PS I)
producing the reductant NADPH [14]. During this linear electron transport, a
proton-motive force is created and used for ATP production. The second stage of
oxygenic photosynthesis includes the dark reactions (independent of light) where
the produced ATP and NADPH are used for CO 2 fixation into carbohydrates
through the Calvin–Benson–Bassham (CBB) cycle [11].
While microalgae and cyanobacteria contain two reaction centers (PS II and PS
I) that operate in series, anoxygenic (non-oxygen evolving) phototrophic bacteria
(APB) contain only one reaction center (Fig. 2).
The reaction center can either be of Type I where light drives the reduction of a
ferredoxin protein or a Type II reaction center (RC II) where the electrons are
donated to quinones [13]. Heliobacteria, Chlorobi, and Chloroacidobacteria employ
Type I reaction centers, while Chloroflexi, Gemmatimonadetes, and phototrophic
members of Proteobacteria employ Type II reaction centers [10, 14]. APB reaction
New Phototrophic Factories for Resource Recovery
415
for virgin raw materials and waste disposal, they have been the key for sustainable
industrial development along the fields of raw material processing like leather, pulp,
and paper production, up to more complex fields of detergent, textile, cosmetics,
and pharmaceuticals production [8, 9]. For the particular case of enzyme utilization
in environmental applications, this chapter will provide an overview of biological
systems that make use of photosynthetic microorganisms and their unique
enzyme-mediated metabolism for the treatment of wastewater, nutrient recovery,
and wastes valorization. A special focus will be given to the case studies of the
photo-enhanced biological phosphorus removal (photo–EBPR) and the phototrophic purple bacteria pond (PPBPond), which are, respectively, two innovative
technologies for phosphorous recovery and polyhydroxyalkanoates production in
illuminated open systems.
2 Diversity of Phototrophic Organisms: Overview
Phototrophy is a process that consists in converting light energy into a usable form
of chemical energy and it can be used by a great diversity of organisms, both
eukaryotic and prokaryotic. While all chlorophyll and/or bacteriochlorophyll containing phototrophs can synthetize ATP from light, one of the most differentiating
features between them regards their electron source and capability of producing
oxygen [10]. Microalgae and cyanobacteria are able to use water as the electron
source and thus, are capable of performing an oxygenic photosynthesis (i.e., oxygen
is produced) in a process that occurs in two distinct stages. The first stage includes
light-dependent reactions and takes place in specialized structures (chloroplasts)
where light energy is absorbed, driving the synthesis of ATP and NADPH in a
process coupled to the formation of oxygen from water (Fig. 1).
Photosystem II (PS II) produces a very strong oxidant (*+1250 mV) that is
capable of oxidizing water to molecular oxygen (+810 mV) [13]. Then, the electrons proceed via cytochrome bf complex to NADP
+ in photosystem I (PS I)
producing the reductant NADPH [14]. During this linear electron transport, a
proton-motive force is created and used for ATP production. The second stage of
oxygenic photosynthesis includes the dark reactions (independent of light) where
the produced ATP and NADPH are used for CO 2 fixation into carbohydrates
through the Calvin–Benson–Bassham (CBB) cycle [11].
While microalgae and cyanobacteria contain two reaction centers (PS II and PS
I) that operate in series, anoxygenic (non-oxygen evolving) phototrophic bacteria
(APB) contain only one reaction center (Fig. 2).
The reaction center can either be of Type I where light drives the reduction of a
ferredoxin protein or a Type II reaction center (RC II) where the electrons are
donated to quinones [13]. Heliobacteria, Chlorobi, and Chloroacidobacteria employ
Type I reaction centers, while Chloroflexi, Gemmatimonadetes, and phototrophic
members of Proteobacteria employ Type II reaction centers [10, 14]. APB reaction
New Phototrophic Factories for Resource Recovery
415