# Microbes and Parameters Influencing Dark Fermentation for Hydrogen Production
## 4 Bacteria Used for Hydrogen Production During Dark Fermentation
### Enterobacter
#### 4.2.1 Enterobacter aerogenes  
_E. aerogenes_ is a facultative anaerbe that produces ATP through oxidative phosphorylation. In the presence of O\({}_{2}\), it grows via aerobic respiration, whereas in the absence of O\({}_{2}\), it switches to anaerobic respiration using alternative electron acceptors. These bacteria produce more H\({}_{2}\) when nanoparticles are added. In a study performed by [PERSON] et al. [123], ferric oxide nanoparticles facilitated dark fermentation by Enterobacter aerogenes and increased the H\({}_{2}\) yield from 1.32 to 1.55 mol H\({}_{2}\)/mol glucose when the ferric oxide nanoparticle concentration was increased from 0 to 200 mg/L. Table 5 presents a list of _E. aerogenes_ strains with their H\({}_{2}\) production abilities using different substrates and operational conditions.  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline \multirow{2}{*}{**Strain**} & \multicolumn{2}{c}{**Substrate**} & \multirow{2}{*}{**Conditions**} & \multicolumn{2}{c}{**Operation Mode**} & \multicolumn{2}{c}{**H\({}_{2}\) Yield as Mol**} \\  & & **(Concentration, g/L)** & & & **(Reactor Volume, mL)** & **H\({}_{2}\)/mol Substrate \({}^{*}\)** & **Ref.** \\ \hline \multirow{6}{*}{DSM 1237} & \multirow{6}{*}{Cellulose (25)} & **T** & \multirow{2}{*}{**pH**} & \multirow{2}{*}{**Time (h)**} & \multirow{2}{*}{**More Details**} & \multirow{2}{*}{**Batch (20)**} & \multirow{2}{*}{1.30 (hexose)} & \multirow{2}{*}{[114]} \\  & & **(\({}^{\circ}\)C)** & & & & & \\ \cline{1-1} \cline{5-7}  & & & 7.3- & & & & \\ \cline{1-1} \cline{5-7}  & & & 7.4 & & & Batch (20) & 1.30 (hexose) & [114] \\ DSM 1313 & Cellulose (5) & 60 & 7.0 & & & 60 rpm & Continuous (2000) & 0.76-121 (hexose) & [115] \\
27405 & & Cellulose (5) & 55 & 7.0 & 168 & & Purged with N\({}_{2}\), & Batch (120) & 1.92 (hexose) & [116] \\ KJC315 & & Cellobiose (5) & 60 & 7.0 & 24 & & Purged with N\({}_{2}\), & Batch (130) & 3.26 (hexose) & [177] \\ DSM1313 & & Cellulose (10) & 55 & & 192 & 105 \(\
u\)/\(\
u\) inoculum, & Batch (130) & 1.15 (hexose) & [118] \\  & & & & & 150 rpm & & & \\ ATCC 27405 & & Cellulose (3) & 55 & & 168 & & 20 mM CaCO\({}_{3}\), 10\% & & \\  & & & & & (\(\
u\)/\(\
u\)) inoculum, & Batch (120) & 5.87 (hexose) & [119] \\  & & & & & 150 rpm & & & \\ \hline \hline \end{tabular}  
* In parentheses, the reference substrate for calculation when it differs from the cited one.  
\end{table}
Table 4: Hydrogen production by different _Clostridium thermocellum_ strains.  
Few studies have been performed with _E. aerogenes_, as summarized in Table 5. The bacteria require the addition of nanoparticles to increase H\({}_{2}\) production, which might be one of the reasons why it has not been widely used for dark fermentation H\({}_{2}\) production studies. It has been observed that this microbe grows well on a variety of substrates and can produce H\({}_{2}\) around 37 \({}^{\circ}\)C. All studies show that continuous agitation in the bioreactor is required to increase bacterial interaction with the substrate, thus yielding more H\({}_{2}\). The maximum H\({}_{2}\) yield of 2.6 mol H\({}_{2}\)/mol sugar was observed using fermentable sugar as the substrate, with the addition of ferric oxide nanoparticles, at 37 \({}^{\circ}\)C for 72 h.