CUI Wen-ming, LIU Lu, ZHANG Shu-wen, PANG Xiao-yang, LI Hong-juan, LV Jia-ping
The optimal conditions for Lactobacillus delbrueckii subsp.bulgaricus LJJ autolysis and the effect of lysozyme on autolysis were determined through analyzing the influence of various factors such as temperature,pH of TE buffer,incubation time,cell growth phase,SDS and Triton X-100 concentration.Autolysis was performed on Lactobacillus delbrueckii subsp.bulgaricus LJJ from different growth stages and detecting the autolysis rate and lysozyme activity variation under various levels of SDS and Triton X-100 concentration.The morphological differences of the normal LJJ cells,the autolysis cells in TE buffer after 24h incubation at 37℃ and in TE buffer with 0.50 g / L SDS were observed by Scanning Electron Microscope(SEM).The results showed that LJJ had the optimum autolysis temperature of 50℃ and the optimum autolysis pH value in the range of 6.0 ~ 8.0.Furthermore,with the extension of incubation time,autolysis rate of LJJ was increasing gradually and the rate increase slowed down significantly after 24h incubation.LJJ cells of the exponential phase showed the maximum autolysis rate,while LJJ cells of the steady growth period gave the minimum autolysis rate.The presence of SDS significantly inhibited the autolysis of LJJ and lysozyme activity.Autolysis of LJJ and lysozyme activity was inhibited by 99.6% and 97.4% with adding 0.50 g / L SDS respectively.In contrast,the use of 1.00 g / L Triton X-100 improved the activity of lysozyme by 20.7% and 39.5% respectively.The results of SEM observation revealed that the autolysis cells in TE buffer after 24h incubation at 37℃ compared to the normal cells had holes appearing in the cell wall,cell integrity was destroyed,and intracellular content dissolved out,while the autolysis cells in TE buffer with 0.50 g / L SDS just became atrophic and the cell surface was crude,but cell wall still kept its integrity.Environmental temperature,pH value,incubation time,cell growth phase,SDS concentration and Triton X-100 concentration can affect the autolysis of LJJ significantly and be used for the regulation of the autolysis of LJJ through controlling the influence factors of autolysins under certain conditions.
