Molecular characterization of the bacterial composition in two waste silk refining systems

Spontaneous fermentation is a traditional and ecologically friendly way to purify silk, but the knowledge of the microbial structure in this system is limited. The fermentation liquids (W1 and W2) from two waste silk refining systems were analyzed for their bacterial community and diversity. W1 had higher oil-removing and degumming efficiency than W2, and so was superior for the recovery of waste silk. The bacterial community structures of W1 and W2 were characterized by polymorphisms in the 16S rRNA gene. Two corresponding clone libraries (C1 and C2) were constructed from each system. Using amplified rDNA restriction analysis (ARDRA), 112 randomly selected clones were grouped in 24 operational taxonomic units (OTUs) from C1 and 113 clones were grouped in 20 OTUs from C2. The bacterial diversity of C1 was higher than C2 according to the Shannon-Weaver index. Sequencing and phylogenetic analysis indicated that Firmicutes were the most dominant group in both samples, followed by Bacteroidetes. Clones related to Synergistetes were only found in C1. This investigation expands substantially our knowledge of the bacterial composition and diversity in waste silk refining systems. The results also revealed that the silk-spinning system may harbor a bacterial population structure suitable for metagenomic mining for novel bacterial lipase, esterase, and protease.