Lactose induced bioproduction by Halomonas grown under open conditions

Abstract

The dynamic regulation of gene circuits using efficient, low-toxicity, and cost-effective inducers has profound implications for the production of a wide range of biological products. Halomonas bluephagenesis, a next generation industrial biotechnology chassis able to grown under open unsterile condition while remains contamination free, was equipped with a synthetic and lactose-induced T7-like induction system against the carbon catabolite repression. This system exhibited comparable efficiency and robustness to the T7-like systems induced by IPTG for the Halomonas with an induction fold change exceeding 350-fold, while offering cost-saving advantages. The lactose-controlled genetic circuit was used to induce heterologous genes for production of acetoin, lysine and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P34HB), forming 2.20 g/L of acetoin, 4.23 g/L of lysine and 5.90 g/L poly(3-hydroxybutyrate-co-9.14 mol% 4-hydroxybutyrate) in shake flasks, respectively, exhibiting an increase of 16 % and 23 % and 26 % for the bioproducts, respectively, compared to the titers achieved under IPTG induction controls. Additionally, lactose induced cell elongation has proven effective for enhanced intracellular polyhydroxyalkanoates (PHA) accumulation, achieving 17 % and 5 % increase in cell dry weight (CDW) and its poly-3-hydroxybutyrate (PHB) content compared to IPTG induction did. Lactose induction in recombinant H. bluephagenesis cultured in a bioreactor resulted in 35 % and 10 % increases in CDW and its PHB content compared to IPTG induction did, respectively. This study demonstrated that the lactose induction system is highly effective combined with cost reduction compared to IPTG for H. bluephagenesis.