The effects of the fermentation conditions on both the biomass yield and the organic selenium yield of Thelephora ganbajun zang were studied. The components most suitable for the submerged fermentation medium were examined using the orthogonal array method; they comprised sucrose at 30 g L(-1) , carbamide 1 g L(-1) , corn steep liquor 8 g L(-1) , MgSO4 ·7H2 O 0.3 g L(-1) , KH2 PO4 0.5 g L(-1) , and NaCl 5 g L(-1) . The optimum cultivation conditions that resulted in maximal biomass yield were obtained using the response surface methodology (RSM). The conditions were as follows: initial pH, 5.84; temperature, 26.16 °C; and rotation speed, 170 rpm. Feeding sucrose led to a higher biomass yield, with a maximum of 21.20 g L(-1) . The biomass yield and the organic Se yield of T. ganbajun could reach 10.8 g L(-1) and 3256.07 mg kg(-1) , respectively, in a culture medium supplemented with 200 mg L(-1) sodium selenite (Na2 SeO3 ), which was added to the medium at 36 h after inoculation. Application of the orthogonal array method and RSM gave rise to a significant enhancement in the biomass yield of T. ganbajun. The results of these experiments indicate that T. ganbajun is a promising microorganism for selenium enrichment.

Abstract. Compared with cereal production, vegetable production usually requires a greater degree of management and larger input of nutrients and irrigation, but these systems are not sustainable in the long term. This study aimed to what extent lettuce determine the bacterial community composition in the soil, during lettuce cultivation, pesticides and fertilizers were not apply to soil. Soil samples were collected from depths of 0-20cm and 20-40cm. A highthroughput sequencing approach was employed to investigate bacterial communities in lettuce -cultivated soil samples in a timedependent manner. The dominant bacteria in the lettuce soil samples were mainly Proteobacteria, Actinobacteria, Chloroflexi, Nitrospirae, Firmicutes, Acidobacteria, Bacteroidetes, Verrucomicrobia, Planctomycetes, Gemmatimo nadetes, Cyanobacteria. Proteobacteria was the most abundant phylum in the 6 soil samples. The relative abundance of Acidobacteria, Firmicutes, Bacteroidetes, Verrucomicrobia and Cyanobacteria decreased through time of lettuce cultivation, but the relative abundance of Proteobacteria, Actinobacteria, Gemmatimonadetes, Chloroflexi, Planctomycetes and Nitrospirae increased over time. In the 0-20cm depth group and the 20-40cm depth soil, a similar pattern was observed that the percentage number of only shared OTUs between the early and late stage was lower than that between the early and middle stage soil, the result showed that lettuce growth can affect structure of soil bacterial communities.

The variation of bacterial community in lettuce continuous cropping was determined by high throughput sequencing. During the continuous planting of lettuce, the richness and diversity of bacterial communities in the soil increased, and the ACE index and Chao index increased by 40.21 % and 36.91 %, respectively. The proportion of Actinobacteria, Chloroflexi, Firmicutes and Nitrospirae in the soil increased, while the abundance of Acidobacteria, Bacteroidetes, Gemmatimonadetes, Planctomycetes and Proteobacteria gradually declined. And the abundance in the soil accounting for 1 % of the dominant bacterial genera increased to 11, among them, Anaerolinea, Bacillus, Nitrosomonas, and Xanthomonas etc became the dominant bacterium genus in the soil after lettuce continuous cropping. After the lettuce had been planted 8 times, the yield decreased by 21.20 % compared to the first harvest. Lettuce continuous cropping had an effect on bacterial community and lettuce yield to some extent.

About 108 retail and 101 field‐grown lettuce samples from across Beijing were examined. These samples were analyzed for their aerobic plate counts, coliform counts, fecal flora counts, and presence of pathogenic bacteria. Samples included retail leaf (n = 56), retail head (n = 52), field‐grown leaf (n = 54), and field‐grown head lettuce (n = 47). The number of aerobic colonies of retail leaf lettuce was significantly higher than that of retail head lettuce throughout the year, with the exception of December. The means of retail leaf lettuce aerobic plate counts varied from 4.87 to 7.03 log10 cfu/g. For retail head lettuce, the mean count of aerobic microbiological populations varied from 4.33 to 6.33 log10 cfu/g. The aerobic microbiological populations of field‐grown lettuce were lower than those of retail lettuce in the same month. The mean count of field‐grown head lettuce was 5.53 log10 cfu/g. The mean count of retail head lettuce was 5.92 log10 cfu/g. The mean of the coliform counts ranged from <0.47 to 2.85 log10cfu/g. Leaf and retail lettuce had significantly higher coliform, fecal flora, and Escherichia coli counts than head and field‐grown lettuce. The detection rate of E. coli was directly proportional to that of fecal flora. No E. coli O157:H7 or Salmonella spp. were detected in these lettuce samples.Practical applicationsIt is generally agreed that microbial contamination of lettuce will arise if there is improper operation in the process of its storage, transportation, and shelves sale. As lettuce is usually eaten raw, microbes can cause people to suffer from illnesses. Therefore, it is of critical importance to monitor the presence of microbes closely. In this study, the number of aerobic plate count in lettuce from different sources was examined. It was found that freshly picked lettuce had fewer microorganisms than retail lettuce had; lettuce harvested in low‐temperature seasons has fewer microorganisms than that in hot seasons. The suggestion is that cold chain transport is the best way for lettuce transportation, especially in summer and aseptic packaging is helpful to reduce contact pollution.