Highly efficient production of hyaluronic acid by Streptococcus zooepidemicus R42 derived from heterologous expression of bacterial haemoglobin and mutant selection.

UNLABELLED: During Streptococcus zooepidemicus fermentation, most carbon sources are used to synthesize lactic acid, which can inhibit strain growth and hyaluronic acid production. Here, we expressed bacterial haemoglobin (Vhb) in Strep. zooepidemicus. Due to highly efficient oxygen use, only 15·26 g l(-1) lactic acid was produced, which is 0·73 times the quantity produced by the control strain. Compared with the control strain (1·61 g l(-1) ), hyaluronic acid (HA) production in this strain did not substantially increase, only to 2·16 g l(-1) . Next, we used a series of N-methyl-N'-nitro-N-nitroso-guanidine (NTG) treatments and selection programmes. Finally, we generated a hyaluronidase-negative and rifampin-resistant mutant strain that produces high levels of HA. The optimum carbon concentration for maximum hyaluronic acid production is only 30 g l(-1) of sucrose, which is lower than the control strain (60 g l(-1) ). The oxygen transfer rate coefficient KL a increased significantly to 372 ± 53 h(-1) from 18 ± 4 h(-1) of the control. The optimum carbon source for this strain is 21 g l(-1) of sucrose, 9 g l(-1) of maltose and 5 g l(-1) of glutamic acid. Hyaluronic acid accumulated at 6·7 g l(-1) in the culture broth. However, the molecular weight of HA decreased from 1835 KDa (Control) to 429 kDa. The prepared low-molecular weight HA could function as potential antiangiogenic substances, antiviral and antitumour agents to possibly be used as functional food ingredients. SIGNIFICANCE AND IMPACT OF THE STUDY: Hyaluronic acid (HA) has been used for a wide range of applications in health, cosmetic and clinical fields. During fermentation of Streptococcus to produce HA, 80-85% of the carbon source is used to produce lactic acid and acetic acid, and only approx. 5 and 10% of the carbon source is used to produce HA and biomass respectively. Here, we expressed bacteria haemoglobin (Vhb) in Streptococcus zooepidemicus, which can dramatically inhibit lactic acid production. After NTG treatments and selection programmes, we identified a mutant strain with highly efficient hyaluronic acid production (6·7 g l(-1) ) under economic fermentation conditions.