## 3 Results and Discussion
### Dynamics and Source of Bacteria during SSF of PFPT  
A heat map of major bacteria (>1%) in tea leaves at the genus level is given in Figure 3a. A PCA analysis is shown in Figure 3b. The bacterial community in the raw material (day 0) was different from those in other samples, with dominant bacteria of _Sphingobacterium_ (16.48%) and _Methylobacterium_ (16.39%). After seven days of fermentation, the dominant bacteria had changed to _Pantoea_ (21.32%) and _Pseudomonas_ (18.87%). In the 14 days of SSF, the genera of _Paenibacillus_ and _Bacillus_ were dominant and accounted for 26.21% and 16.73% of total reads, respectively. _Achromobacter_ (17.62%) was dominant at 21 days. In the sample collected on day 28 of SSF, the dominant bacteria were identified as _Staphylococcus_ (20.78%) and no_rank_Dermabacteraceae (16.91%). At the last stage of SSF (day 35), no_rank_Dermabacteraceae (30.82%) were dominant, followed by _Staphylococcus_ (19.62%). At the phylum level, the pyrosequencing analysis indicated that the dominant bacteria were Proteobacteria, Firmicutes and Actinobacteria. By metagenomic analysis, [PERSON] showed that dominant bacteria in one fermented sample of PFPT were Proteobacteria (23.56%), Actinobacteria (23.35%), and Firmicutes (11.37%) [12]. By using a 16S rRNA gene clone library, we also demonstrated that the dominant bacteria during SSF of PFPT were Proteobacteria and Firmicutes [7]. Recently, [PERSON] identified that the most commonly observed bacterial taxa in 31 Pu-erh tea samples belonged to Firmicutes, Actinobacteria, and Proteobacteria [14]. These samples in different reports have similar dominant bacteria, suggesting that Proteobacteria, Firmicutes, and Actinobacteria may be the core bacteria in SSF of PFPT, and they may play crucial roles in the quality formation of the PFPT. However, more samples from different areas and producers should be investigated to validate this hypothesis.  
To investigate the sources of the bacteria, a series of comparisons of major bacteria (>1%) at the genus level were performed (Figure 4). A comparison of raw material and the seven-day fermented sample showed that they shared six bacterial genera, which accounted for 67.79% of the total reads of seven-day fermentation (Figure 4a). This revealed that partial bacteria in initial stages of SSF came from the raw material. Additionally, four genera were newly detected in the seven-day fermented sample. This demonstrated that a portion of the bacteria came from the fermentation environment (room, air, or water). Comparisons of bacterial genera between the samples of day 7 and 14, day 14 and 21, and day 21 and 28 showed that six, six, and five genera, respectively, accounting for 55.49%, 18.61%, and 26.89%, respectively, of each sample's reads were newly detected. A comparison of 35-day-fermented tea leaves and raw material showed that they shared only 18.35% of bacteria (Figure 4f). Together, these comparisons indicated that active bacteria were from the raw material and fermentation environment during the initial stages, and the bacteria in the fermentation environment continued to naturally inoculate into tea mass during the SSF. This primary comparison suggested that environmental bacteria are involved in the fermentation of PFPT; this is possibly the reason for the geographical characteristics of PFPT.  
Figure 3: Heat map of relative abundances of major bacterial genera (>1%) (**a**); principal component analysis (PCA) analysis of bacterial communities in fermented tea leaves during the SSF of PFPT based on the relative abundances of the sample reads at the genus level (**b**).