Chinese traditional vinegars generally use qu as a starter for vinegar fermentation.Among them,daqu is a famous starter.Qu is a starter culture which is added to the raw material to produce traditional fermentation food,such as vinegar,by accelerating and steering its fermentation process.Different from pure species starter,qu is a mixed starter contained many bacteria,moulds and yeasts which are used to saccharize and ferment rice and cereals.There are several kinds of Qu in China,daqu (with a red core),hongqu (red yeast rice),xiaoqu (made of rice and rice chaff in an egg-shaped form),fuqu (made of wheat bran by inoculating a pure culture of Aspergillus spp.) and maiqu (made with wheat in brick-shaped form).Daqu is also used in Tianjin duliu mature vinegar.Same as other traditional vinegars,the fermentation of Tianjijn duliu mature vinegar includes three steps,starch saccharification,alcohol fermentation and oxidation of ethanol to acetic acid.Tianjin duliu mature vinegar is produced in Tianjin,locates in north of China,and there is still little studies on microbial community of daqu in Tianjin Duliu mature vinegar (duliu-daqu).The duliu-daqu is prepared in special environment with spontaneous growth of microorganisms including moulds,yeasts and bacteria.The flavor substances in vinegar mainly come from the metabolites of microbial community.It is helpful to study the relationship of bacterial community with the flavor,which could elucidate the flavor formation mechanism of traditional vinegar.The preparation of duliudaqu is fermented spontaneously and controlled empirically,and the microorganisms in duliu-daqu construct a community.So far,the microbial composition of duliu-daqu is still unknown,and it is currently impossible to make a rational approach to control the microbial community and to improve the flavor.The composition of microbial community could be investigated by using culture-dependent and culture-independent methods.However,culture-based approaches have known limitations in terms of reproducibility and challenges in the culturability of some microorganisms.Thus the true composition of microbial community may still not be reflected by the cultured isolates.Over the past decades,many biological methods have been developed for analysis of microbial community structure.Analysis of 16S/18S rDNA clone library,denaturing gradient gel electrophoresis (DGGE) and temperature gradient gel electrophoresis (TGGE) are effective methods for community structural analysis.In the present study,DGGE fingerprinting was applied to study the bacterial community in duliu-daqu.The results showed that bacterial community in duliu-daqu was composed with genus of Weissella,Lactobacillus,Lactococcus,Streptomyces and uncultured bacteria.There were a high level of species diversity of Streptomyces,including Streptomyces rangoonensis,Streptomyces cacaoi subsp.cacaoi,Streptomyces cacaoi,Streptomyces gibsonii,Streptomyces radiopugnans,Streptomyces albus subsp.albus and Streptomyces albus,which were all first reported in duliu-daqu.