Page 56 - Biofuels Refining and Performance

Energy and Its Biological Resources 39

Enzymatic. Glucose dehydrogenase oxidizes glucose into gluconic acid

and NADPH, which helps the reduction of H by hydrogenase. Glucose
dehydrogenase and hydrogenase are purified from Thermoplasma aci-
dophylium and Pyrococcus furiosus (optimal growth at 59 C and 100 C,
respectively) (Woodward).
Based on metabolic patterns, the microbial systems may be of four types:
mediated through NADPH
1. Photosynthetic microbes evolving H 2
(Nicotine Adenine Dinucleotide Phosphate [Coenzyme II-reduced]) by
photoenergy.
2. Cytochrome systems operating in facultative anaerobes that convert
mainly formates to H .
2
3. Cytochrome containing strict anaerobe, Desulfovibrio desulfuricans.
4. Clostridia, micrococci, methanobacteria, and others, without
cytochrome, anaerobic heterotrophs.
Klebsiella oxytocae. ATCC (American Type Culture Collection) 13182
can convert formates to H (100%), but only 2 moles of H for each mole
2
2
of glucose (5%). C. butyricum can convert glycerol to 1,3-propanediol,
butyric acid, 2,3-butanediol, formic acid, and CO and H . Klebsiella
2
2
pneumoniae can convert glycerol into 1,3-propanediol, acetic acid, formic
acid, and CO and H . The presence of acetate enhances the production
2
2
of butyrates and H , and less propanediol.
2
Before discussing cyanobacteria and photosynthetic bacteria, we
should review the basic reactions involved in photosynthesis, i.e., steps
in so-called photophosporylation:
hv
H O NADP PO ADP ⎯→ O NADPH H ATP
2
2
4
hv

CO NADPH H ATP ⎯→ (HCOH) NADP ADP PO 4
n
2
hv
Aerobic: 6CO 6H O ⎯→ C H O 6O 2
6
12
2
2
6
hv
Anaerobic: Isopropanol or H S CO ⎯→ Acetone or S
2
2
(CH O) H O
n
2
2
Cyanobacteria. Popularly known as blue-green algae, and justifiably
so (they consume CO and evolve O ), they are bacteria (absence of
2
2
nuclei, mitochondria, chloroplasts, etc.) as well as algae.
Cyanobacteria are oxygenic photoautotrophs, possessing photo I and
II systems. Cyanobacteria have been well studied, and the details of
their physiology and biochemistry are available in reviews and books.
They are held by many scientists as potential sources of chemicals, bio-
chemicals, food, feed, and fuel. Most of them are molecular nitrogen
production. They are
fixers and possess a nitrogenase system for H 2