Photoheterotrophic growth of purple non-sulfur bacteria on Tris Acetate Phosphate Yeast extract (TAPY) medium and its hydrogen productivity in light under nitrogen deprivation

Abstract

In this study, an active photoheterotrophic growth of purple non-sulfur bacteria (PNSB) on Tris Acetate Phosphate Yeast extract (TAPY) medium is reported. TAPY medium is a modified TAP medium supplemented with filter sterilized yeast extract (0.3 g L−1) and vitamin B12. Heterotrophic growth of PNSB on nitrogen replete TAPY medium in dark could be obtained but much slower than that in light where cells could grow but without formation of pigments. The medium showed high potency for hydrogen production under nitrogen deprivation in light by Rhodobacter sphaeroides DSM 5864. Through using TAPY medium, 1 mole of acetate provided as glacial acetic acid produced 0.819 mole of hydrogen gas by R. sphaeroides on nitrogen deprived TAPY medium (initial pH 7 adjusted by HCl) with a maximum H2 production rate of (0.669 mmol H2 h−1 L−1) obtained at 42 h after start of fermentation. Repeated-batch hydrogen production could be achieved with high efficiency for three cycles by supplementing the nitrogen deprived culture with filter sterilized sodium acetate at the end of the log hydrogen production phase of each cycle. The medium was also applicable for photoheterotrophic growth in light and heterotrophic growth in dark of other PNSB namely Rhodobacter capsulatus JCM-21090 and Rhodospirillum rubrum DSM 467. Although R. rubrum could actively grow on TAPY medium under nitrogen deprivation in light, it was the lowest in hydrogen production compared to R. sphaeroides and R. capsulatus. The active growth of R. rubrum on nitrogen deprived TAPY medium suggests its possible use for producing biodegradable plastic polymers better than hydrogen. The results suggest that it's possible to use TAPY medium for growth and producing variable bioproducts by PNSB in future studies and applications. The repeated-batch hydrogen production by R. sphaeroides on nitrogen deprived TAPY medium is promising for large-scale applications of hydrogen production industry by only sequential supply with sodium acetate to the culture for three rounds of batch fermentation. This is the first report in using TAPY medium for growth and hydrogen production by PNSB.