Different biotic and abiotic elicitors influence betalain production in hairy root cultures of Beta vulgaris in shake-flask and bioreactor

The hairy roots of Beta vulgaris grow on a simple medium producing good levels (1.2% or 88.4 mg L−1) of betalains—a red water-soluble food colourant. In an attempt to enhance betalain productivity, the hairy roots were contacted with several biotic elicitors such as purified glycans of microbial origin (200–500 mg L−1), extracts of whole microbial cultures (0.25–1.25%) and the respective culture filtrates (5–25%, v/v). Similarly, abiotic elicitors, particularly metal ions, upto 10-folds of that present in the nutrient (MS) medium, were tested. It was observed that though there was a significant suppression of biomass in almost all the treatments, a significantly high productivity of betalain was observed in Penicillium notatum DCP-treated cultures (158 mg L−1 on 7th day) among biotic elicitors, pullulan-treated cultures (202 mg L−1 on 10th day) among purified glycans and calcium treated cultures (127 mg L−1 on 7th day) among abiotic elicitors, whereas control cultures showed productivities of only 43.3 mg L−1 on 7th day and 88.4 mg L−1 on 10th day. Since most of the elicitors caused early elicitation (on 7th day) and suppressed biomass resulting in reduced overall productivity, a strategy of using elicitor at late exponential growth phase was considered and such a strategy was adoptable to scaled up process using a bubble-column bioreactor, where too the addition of elicitor at late exponential phase resulted in about 47% higher productivity of betalains. The present study is the first report where a large number of elicitors are systematically screened and used for scaled-up production of betalains.