# Photo-Fermentative Bacteria Used for Hydrogen Production
## 2 Photo-Fertanative Bacteria for Hydrogen Production
### Rhodospirillum rubrum  
R. rubrum is a spiral, purple photosynthetic bacterium of the genus _Rhodospirillum_ in the class Alphaproteobacteria. The bacteria are anoxygenic phototrophs that produce extracellular elemental sulfur instead of oxygen while harvesting light with their single complex LH1 _rubrum_ and are found in stagnant freshwater ecosystems [79]. A carotenoid spirilloxanthin is bound to the LH1 complex, which has 16 subunits observed by electron microscopy [78]. These bacteria use similar carbon sources to other purple photosynthetic bacteria, including acetate, malate, glucose, fructose, and sucrose, while producing hydrogen [79]. Different strains of these bacteria were used in the PBRs to produce hydrogen and to determine exergy, which is the useful work potential or the available energy. In a study using _R. rubrum_ (ATCC 10801), acetate was used as the carbon source in a 2 L Biostat (Sartorius, Goettingen, Germany) PBR at 30 \({}^{\circ}\)C, 1 atm, with 0-0.85 mL/min flow rates of liquid media, stirring at 150-500 rpm with a total of 540 h of continuous hydrogen production. Tungsten lamps with an average irradiance of 11.85 W/m\({}^{2}\) were used as the light source, and gas samples were analyzed by gas chromatography. The process exergy efficiency was in the range of 14.71-22.90% under optimal conditions and 14.71-22.84% using conventional and eco-exergy concepts [80]. Another study demonstrating the efficiency of _R. rubrum_ in the batch hydrogen production process was analyzed \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref.** & **Strain** & **Substrate** & **Concentration, mM** & **Conditions** & **PBR** & **Light Source** & **Irradiance** & **Hydrogen** \\  & & **(Concentration, mM)** & & & & & **(W/m\({}^{2}\))** & **Rate (mM/h)** \\ \hline
[69] & O.U.001 & Acetic (4) + btwtric acid (6) & pH 7.0, 32 \({}^{\circ}\)C & Batch mode and fed-batch & Ultra-Vitalux lamps (Osram, Permasetate, Austria) & 192 & 0.89 \\
[70] & S10 & Oil palm + mixture of glucose (36.13), xylose (102.56), acetic acid (48.81) & pH 7.0, 35 \({}^{\circ}\)C & 500 mL serum cylinder reactors, batch & Tungsten lamps & 79 & 1.4 \\
[71] & DSM 158 & (30\%) & pH 7.2, 30 \({}^{\circ}\)C & 120 mL clear glass & Halogen lamp & 126 & 0.74 \\  & Restaurant effluent & pH 7.6, 30 \({}^{\circ}\)C & & & & & \\
[72] & HY01 & Glucose (40) & pH 6.9, 35 \({}^{\circ}\)C & 350 mL & Halogen lamp & 31.6 & 5.6 \\
[73] & CIP 60.6 & Lactate (50) & pH 7.5, 30 \({}^{\circ}\)C & Column reactor & Tungsten lamp & 35.6 & 1.8 \\
[74] & DSM 158 & Lactic acid (40) & pH 7.0, 30 \({}^{\circ}\)C & Single-walled glass vessel, batch & Halogen lamp & 2250 & 8.7 \\  & DSM 158 & Lactic acid (40) & pH 7.0, 30 \({}^{\circ}\)C & & & & \\  & & & & 20 L feed tank, continuous & & & \\
[75] & O.U.001 & DL malic acid (15) & pH 6.8, 33 \({}^{\circ}\)C, & Triple-jacketed vertical glass PBR (1 L) & Humaine & & \\  & & & & & & tubular light (Siamen, China) & & \\
[76] & HY01 & Acetate (25) + btwtrate (34) & pH 7.0–8.2, 30 \({}^{\circ}\)C & 30 mL syringes, batch & Tungsten lamp & 31.6 & 7.0 \\
[77] & DSM 158 & DL malic acid (7.5) & pH 6.5–8.0, 30 \({}^{\circ}\)C & 120 mL glass & & Halogen lamp & 35–185 & 1.9 \\
[78] & O.U.001 & L-malic acid (15) & pH 7.0–7.2, 28 \({}^{\circ}\)C & 25 mL sodium & Mercury-tungsten lamp & 116 & 1.2 \\  & [PERSON] and Pfenning media + 20\% & & & & & & 1.1 \\  & wastewater & & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Hydrogen-producing _R. subaeroides_ strains used in PBRs. using different carbon sources, including formate, acetate, malate, glucose, fructose, and sucrose, to support microbial growth. The process used both conventional exergy and eco-exergy concepts to evaluate the exergy efficiency, simultaneously produced molecular hydrogen and identified acetate as the optimal substrate for hydrogen production. A pH of 7.5, 60 W tungsten lamps with a uniform irradiance of 7.9 W/m\({}^{2}\), a pressure of 1 atm, and a constant speed of 200 rpm were used to produce hydrogen.