UvrA expression of Lactococcus lactis NZ9000 improve multiple stresses tolerance and fermentation of lactic acid against salt stress

Abstract

Lactococcus lactis is subjected to several stressful conditions during industrial fermentation including oxidation, heating and cooling, acid, high osmolarity/dehydration and starvation. DNA lesion is a major cause of genetic instability in L. lactis that usually occurs at a low frequency, but it is greatly enhanced by environmental stresses. DNA damages produced by these environmental stresses are thought to induce DNA double-strand breaks, leading to illegitimate recombination. Nucleotide excision repair (NER) protein UvrA suppresses multiple stresses-induced illegitimate recombination. UvrA protein can survive a coincident condition of environmental harsh conditions, multiple stress factors supposedly encountered in the host and inducing UvrA in L. lactis. In this study the expression of UvrA and growth performance and viability of control strain L. lactisVector and recombinant strain L. lactisUvrA under multiple stress conditions were determined. The recombinants strain had 30.70 and 52.67% higher growth performances when subjected to acidic and osmotic stresses conditions. In addition, the L. lactisUvrA strain showed 1.85-, 1.65-, and 2.40-fold higher biomass, lactate production, and lactate productivity, compared with the corresponding values for L. lactisVector strain during the osmotic stress. Results demonstrated NER system is involved in adaptation to various stress conditions and suggested that cells with a compromised UvrA as DNA repair system have an enhanced protection behavior in L. lactis NZ9000 against DNA damage.

Keywords: Lactate productivity; Lactococcus lactis NZ9000; Multiple stresses; UvrA expression.

Fig. 1

a Schematic overview of the construction procedure of the expression plasmid pNZ8148/uvrA. b SDS–PAGE analysis of the expression of UvrA using NICE in L. lactisVector and L. lactisUvrA. M: protein standard marker. The positions of the molecular mass markers are shown on the left side of the panel; Lanes 1 and 3 cell extracts of L. lactisVector and L. lactisUvrA at time zero; Lanes 2 and 4 cell extracts of L. lactisVector and L. lactisUvrA induced with nisin. Arrow indicates the corresponding protein

Fig. 2

Growth performance of L. lactisVector (squares) and L. lactisUvrA (circles) during various environmental stresses: a 40 °C; b pH 5.0; c 3% NaCl; d 0.1 mmol/L H₂O₂. Error bars indicate standard deviations (n = 3)

Fig. 3

Survival rates of L. lactisVector (squares) and L. lactisUvrA (circles) under osmotic stress (a), acid stress (b) cold stress (c) and heat stress (d). Cultures were subjected to osmotic stress (15% NaCl), acid stress (pH 4.0), cold stress (−20 °C) and Heat stress (46 °C) for various times and the survival rate was determined

Fig. 4

Lactic acid fermentation curves by L. lactisVector and L. lactisUvrA during osmotic stress. L. lactisVector (open symbols) and L. lactisUvrA (closed symbols) were cultivated at 30 °C in the absence (a) or presence (b) of 3% NaCl. Circles, triangles and squares represent growth, lactate production and glucose utilization, respectively. Error bars indicate standard deviations (n = 3)