Diversity and composition of microbiota during fermentation of traditional Nuodeng ham.

The microbial community is one of the most important factors in shaping the characteristics of fermented food. Nuodeng ham, traditionally produced and subjected to 1-4 years of fermentation, is a dry fermented food product with cultural and economic significance to locals in southwestern China. In this study, we aimed to characterize the microbiota and physicochemical profiles of Nuodeng ham across different stages of fermentation. Ham samples from each of the four years were analyzed by sequencing bacterial 16S rRNA gene and fungal internal transcribed spacer sequence, in order to characterize the diversity and composition of their microflora. A total of 2,679,483 bacterial and 2,983,234 fungal sequences of high quality were obtained and assigned to 514 and 57 genera, respectively. Among these microbes, Staphylococcus and Candida were the most abundant genera observed in the ham samples, though samples from different years showed differences in their microbial abundance. Results of physicochemical properties (pH, water, amino acid, NaCl, nitrate and nitrite contents, and the composition of volatile compounds) revealed differences among the ham samples in the composition of volatile compounds, especially in the third year samples, in which no nitrite was detected. These results suggest that the structure and diversity of microbial communities significantly differed across different stages of fermentation. Moreover, the third year hams exhibits a unique and balanced microbial community, which might contribute to the special flavor in the green and safe food products. Thus, our study lends insights into the production of high quality Nuodeng ham.

Phylogeographic structures of the host insects of Ophiocordyceps sinensis.

A fungus-insect complex, known as DongChong XiaCao, is formed from the infection of the hepialid larvae by the fungus Ophiocordyceps sinensis, which is endemic to the Qinghai-Tibetan Plateau (QTP). Due to previously limited sample collection size, the data about the diversity and structure of the host insect was insufficient and lacked details. The purpose of this study was aimed to discuss the diversity and phylogeography of the host insects of O. sinensis with a large-scale sampling. The mitochondrial cytochrome oxidase I gene (cox1) was sequenced and analyzed among 710 samples representing 88 geographic locations. 205 haplotypes of cox1 were identified from all the 710 samples and 4 phylogenetic clades with 12 subclades were identified. Instead of the single latitude-based divergence suggested previously, three distribution patterns were deduced to correspond to the phylogeographic structures, including but not limited to the co-existence of a wide and specific local phylogeographic distribution structures. Two separate genetic diversity and differentiation centers, namely the northwestern Yunnan and the southeastern Tibet were identified. Dating analyses from three calibrations supported that the divergence of the 4 clades occurred in the Oligocene-Miocene period (30.54-13.66 million years ago) (Ma), which were connected with the second and third geological movements of the QTP (17-25, 8-13 Ma). Our results provide a more detailed understanding of the divergence and distribution patterns of the host insects of O. sinensis.