Inhibited growth of Clostridium butyricum in efficient H2-producing co-culture with Rhodobacter sphaeroides

Abstract

Cell number of Clostridium butyricum and Rhodobacter sphaeroides in co-culture was measured using q-PCR approach. During efficient H photoproduction from starch (6.2 mol H/mol glucose), Clostridia growth and starch-hydrolyzing activity was partly suppressed. Apparently, the effect of R. sphaeroides towards C. butyricum was not attributed to altered E or pH values in the presence of purple bacteria. Further, disk-diffusion test proved that R. sphaeroides was capable of producing inhibitors against another purple bacterium, Rhodospirillum rubrum, but not against C. butyricum. We suggested that at initial cell number ratio C. butyricum:R. sphaeroides 1:1 purple bacteria outcompeted C. butyricum for yeast extract at its low concentration (80 mg/L). Under these conditions, the H yield was rather high (5.7 mol/mol). When the yeast extract concentration increased to 320 mg/L, this process was replaced by the low-yield H production (1.8 mol/mol) characteristic of Clostridia. However, increased percentage of purple bacteria in inoculum under these conditions prevented this shift. The outcome of competition depended on both the yeast extract concentration and cell number ratio. Apparently, the competition for yeast extract helped to maintain balance between fast-growing C. butyricum and slower-growing R. sphaeroides for efficient H photoproduction.

Dynamic immobilization of bacterial cells on biofilm in a polyester nonwoven chemostat

“…The PCR mixture included 10 μL SYBR Premix Ex Taq ™ (Takara Bio Inc., Dalian, China), 0.4 μL ROX Reference Dye II, 0.8 μL (0.4 μM) forward primer and reverse primer, and 6 μL ddH 2 O. The amplification conditions comprised the following steps: at 95 ℃ for 30 s, 40 cycles at 95 ℃ for 5 s, and 60 ℃ for 30 s. The primers used for qPCR amplification are shown in Table 1 (Sun et al 2010 ; Laurinavichene et al 2010 ; Larsen et al 2013 ). Using the Student’s t -test, statistically significant differences between groups were assessed.…”