变形链球菌luxS基因在硫代谢中的功能研究

Function of luxS gene in sulfurmetabolism of Streptococcus mutans

目的 采用前期实验已构建成功的luxS基因缺失的变形链球菌突变株,分析luxS基因在口腔变形链球菌的密度感应及硫代谢中的双重作用.方法 在不同硫限定条件培养基（半胱氨酸、蛋氨酸、标准株无菌上清液、S-腺苷高半胱氨酸、S-腺苷甲硫氨酸,空白对照为脑心浸液培养基）中分别对不同培养时间（24、48 h）的变形链球菌标准株和突变株的生长进行吸光度值（A值）的测定与分析,通过激光扫描共聚焦电子显微镜观察测定并比较不同培养条件下两菌株生物膜厚度的差异.结果 在半胱氨酸培养基中培养48 h,突变株生长A值及生物膜厚度均有所增长,分别为（1.301±0.009）和（45.009±0.429）μm,但未及标准株水平（P＜0.05）;在蛋氨酸及S-腺苷高半胱氨酸培养基中培养24 h,突变株的生长A值及生物膜厚度与空白对照相比均有所补充,在蛋氨酸培养基中突变株的生长A值及生物膜厚度分别为（0.448±0.028）和（37.068±2.392）μm,在S-腺苷高半胱氨酸培养基中,突变株的生长A值及生物膜厚度分别为（0.460±0.005）和（27.343±1.107）μm,但均未及标准株水平（P＜0.05）,48 h时达到标准株水平;在标准株上清液培养基中突变株的生长A值及生物膜厚度均明显增高且超过标准株水平;在S-腺苷甲硫氨酸培养基中两菌株的生长A值及生物膜厚度与空白对照相比均有不同程度的降低.结论 luxS基因在变形链球菌中不但具有密度感应功能,在硫代谢方面也发挥着一定作用.

Objective To investigate the function of luxS in sulfurmetabolism of Streptococcus mutans （Sm）. Methods The growth with absorbency（A） of the standards and mutant strains was measured and analyzed in the sulfur-limited defined medium at different periods. The laser scanning confocal microscopy（ LSCM ） was used to observe and compare the biofilm thickness of the two kinds of strains at different culture conditions. Results The significant increases in the thickness of mutant strain biofilm and its growth were observed after the addition of cysteine, but did not reach the standards strain levels （ P ＜0. 05）. The growth and the biofilm thickness of the mutant strains were （ 1. 301 ±0. 009） and （45.009 ±0. 429） μm. When methionine and S-adenosylhomocysteine of certain concentrations were respectively added, the biofilm thickness and the growth of mutant strain were raised but did not reach the level of the standards strain at 24 h（ P ＜0. 05 ）, but at 48 h they did. When the methionine was added in the mutant strains for 24 h, the biofilm thickness and the growth of mutant strain were （0. 448 ± 0. 028 ） and （ 37. 068 ± 2. 392 ） μm, as for the adding of S-adenosylhomocysteine were （0. 460 ± 0. 005 ） and （ 27. 343 ±1. 107 ） μm. When adding the supernatant fluid of standard strains, the biofilm thickness and the growth levels of mutant strain were much higher than those of the standards strain. The biofilm thickness and growth of both kinds of strains decreased after the addition of S-adenosylmethionine. Conclusions luxS gene plays not only a role in quorum sensing but also a role in sulfurmetabolism.