Comparison of Hydrogen Production Efficiency by Rhodopseudomonas palustris MP3 and Rhodopseudomonas harwoodiae SP6 Using an Iron Complex as an Enhancement Factor

Abstract

In the present study, an iron(II)-nanoscale organic complex (Fe-NO) was used as an enhancement factor by two different Rhodopseudomonas species of purple non-sulphur bacteria (PNSB) to produce hydrogen (H2). The Fe-NO complex was synthesised using FeSO4·7H2O and Eucalyptus viminalis—a native Australian plant leaf extract—in a 1:2 and 2:1 concentration ratio. Besides, FeSO4·7H2O was also used as a source of iron(II) for comparison with the Fe-NO complex. The photo-fermentative bacterial cultures were isolated from a fishpond, and only two strains, MP3 and SP6, were found viable after several attempts of quadrate streaking. After phylogenetic analysis, these strains were designated as R. palustris MP3 and R. harwoodiae SP6. After comparison with the control, the results showed that the PNSBs manifested an approximately 50% higher H2 yield when the 1:2 Fe-NO complex was used in the fermentation broth at 10 mg/L concentration, where 10.7 ± 0.54 and 10.0 ± 0.49 mL H2/L were obtained by R. palustris MP3 and R. harwoodiae SP6, respectively. The study revealed that the 1:2 Fe-NO complex could be an important material for efficient H2 production.