# Photo-Fermentative Bacteria Used for Hydrogen Production
## 2 Photo-Fertanative Bacteria for Hydrogen Production
### Rhodobacter
#### 2.3.2 Rhodobacter sphaeroides  
_R. sphaeroides_ is a photosynthetic bacterium found in freshwater and marine ecosystems with a metabolism that produces hydrogen under illumination in the presence of an inert, anaerobic atmosphere. The conditions for hydrogen production must be carefully adjusted, but sometimes it is unavoidable and an alternative mode prevails, and the microbe can modify its metabolic pathways due to its versatile metabolism [68].  
These bacteria, like other PNSBs, have bacteriochlorophyll, which absorbs photons and converts them into chemical energy. NiFe hydrogenases, which catalyze the formation of molecular hydrogen, are commonly found in these bacteria. A list of certain conditions for the use of this microbe to produce hydrogen, which have been studied in various research papers, is given in Table 4.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Ref.** & **Strain** & \begin{tabular}{c} **Substrate** \\ **(Concentration, mM)** \\ \end{tabular} & **Conditions** & **PBR** & **Light Source** & \
\begin{tabular}{c} **Irradiance** \\ **(W/m2)** \\ \end{tabular} &
\begin{tabular}{c} **Hydrogen** \\ **Production** \\ **Rate (mM/h)** \\ \end{tabular} \\ \hline
[59] & JP91 & Glucose (56) & pH 6.8, 30 \({}^{\circ}\)C & 350 mL, continuous & Tungsten lamp & Not described & 1.6–2.3 \\
[60] & JP91 & Glucose (35) & pH 6.8, 30 \({}^{\circ}\)C & 100 mL serum bottles, batch & Tungsten lamp & 175 & 2.6 \\
[61] & DSM 1710, YO3 & Acetate (60) & pH 6.7, 30–32 \({}^{\circ}\)C & 1.4 L PMMA reactor, batch & Tungsten lamp & 200 & 0.75–1.3 \\
[62] & DSM 1710 & Acetic acid (40) & pH \(<\) 8, 10–35 \({}^{\circ}\)C & 80 L tubular PBR & Artificial light source & \textgreater{}90 & 0.52 \\
[63] & DSM 1710 & \begin{tabular}{c} Lactic acid \\ (7.5) \\ \end{tabular} & pH 6.4, 27.5 \({}^{\circ}\)C & 55 mL glass bottle & Tungsten lamp & 287 & 0.566 \\  & \
\begin{tabular}{c} Sucrose (5 \\ indoors, 10 \\ outdoors) \\ \end{tabular} & pH 7.5, 30 \({}^{\circ}\)C & 3.64 L PBR of two & Tungsten lamps &
\begin{tabular}{c} \\ (indoors), \\ \end{tabular} & 200 & 0.73 (indoors), 0.87 (outdoors) \\
[65] & Wild type B10 & Lactate (35) & pH 6.9, 30 \({}^{\circ}\)C & 350 mL cylindrical & Na lamps, LEDs & 812, 479 & 0.26–0.46 \\
[66] & DSM 1710 & Acetate (20) & pH \(<\) 8, \textless{}35 \({}^{\circ}\)C & Tubular PBR (90 L), fed-batch & Halogen lamp & 200 & 0.15 \\
[67] & MT1131 & Acetate (20) & pH \(<\) 8, \textless{}30 \({}^{\circ}\)C & Tubular PBR (90 L), fed-batch & Halogen lamp & 200 & 0.20 \\ \hline \hline \end{tabular}
\end{table}
Table 3: Hydrogen-producing _R. capsulatus_ strains used in PBRs.  
R. subaeroides_ has been analyzed in several studies with different carbon sources and has shown great potential as a renewable and environmentally friendly source with the ability to convert organic compounds into hydrogen gas. Further optimization of the environmental conditions for its growth and genetic engineering of its strains helps to enhance its hydrogen production capabilities, making this microbe an efficient candidate for the development of green energy.