Optimization of pH and nitrogen for enhanced hydrogen production by Synechocystis sp. PCC 6803 via statistical and machine learning methods

Abstract

The nitrogen (N) concentration and pH of culture media were optimized for increased fermentative hydrogen (H(2)) production from the cyanobacterium, Synechocystis sp. PCC 6803. The optimization was conducted using two procedures, response surface methodology (RSM), which is commonly used, and a memory-based machine learning algorithm, Q2, which has not been used previously in biotechnology applications. Both RSM and Q2 were successful in predicting optimum conditions that yielded higher H(2) than the media reported by Burrows et al., Int J Hydrogen Energy. 2008;33:6092-6099 optimized for N, S, and C (called EHB-1 media hereafter), which itself yielded almost 150 times more H(2) than Synechocystis sp. PCC 6803 grown on sulfur-free BG-11 media. RSM predicted an optimum N concentration of 0.63 mM and pH of 7.77, which yielded 1.70 times more H(2) than EHB-1 media when normalized to chlorophyll concentration (0.68 +/- 0.43 micromol H(2) mg Chl(-1) h(-1)) and 1.35 times more when normalized to optical density (1.62 +/- 0.09 nmol H(2) OD(730) (-1) h(-1)). Q2 predicted an optimum of 0.36 mM N and pH of 7.88, which yielded 1.94 and 1.27 times more H(2) than EHB-1 media when normalized to chlorophyll concentration (0.77 +/- 0.44 micromol H(2) mg Chl(-1) h(-1)) and optical density (1.53 +/- 0.07 nmol H(2) OD(730) (-1) h(-1)), respectively. Both optimization methods have unique benefits and drawbacks that are identified and discussed in this study.

Effects of selected electron transport chain inhibitors on 24-h hydrogen production by Synechocystis sp. PCC 6803

“…Initial screening experiments were conducted using both a colorimetric screening assay (Schrader et al, 2008) and gas chromatograph (GC)-vial experiments, with H 2 and CO 2 accumulations in the headspace of GC vials measured by injections of headspace gas into a GC (Agilent Series 6890N, Agilent Technologies Inc., Santa Clara, CA, USA) as described by Burrows et al (2009). All GC-vial experiments in this study used 4-mL vials.…”

“…PCC 6803 during full light, full dark, and light/dark cycling conditions were investigated. Using Response Surface Methodology (RSM) (Myers and Montgomery, 2002) and the Q2 algorithm (Moore et al, 1998;Burrows et al, 2009) in conjunction, optimal concentrations of inhibitors shown in initial screening experiments to bring about the highest production of H 2 were found. The results suggest that partial knockouts of pathways involved in the electron transport chains could be beneficial for 24-h H 2 production.…”

Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

“…Excess Ni could favor bidirectional hydrogenase synthesis and H 2 production by this enzyme. In addition, culture conditions can be optimized for maximal cyanobacterial H 2 production (40,41).…”

Growth and hydrogen production of outdoor cultures of Synechocystis PCC 6803

“…These differences in performance between laboratory and outdoor culture indicate that there is enough room for improvement in H 2 output. Essential enhancements in hydrogen production by non-nitrogen-fixing cyanobacteria have been achieved through the optimization of cultivation conditions, such as pH control of the medium [9], and nutrient supply [48,49]. These last authors, suggested that instead of completely starving cells of essential nutrients, the highest hydrogen production in Synechocystis cultures occurred with a limitation on ammonia and sulfate to a certain level, and with an additional supply of carbon in the form of bicarbonate anion.…”