Sequencing results and samples diversity
A total of 16 samples(healthy vaginal secretion (HV, N = 4), healthy feces (HF, N = 4), endomentritis vaginal secretion (EV, N = 4), endomentritis feces (EF, N = 4)) were collected from 8 sows in a farm. Samples total DNA were extracted and sequenced on Ion S5 XL platform. After cutting off the barcodes, primers and filtering low-quality reads, chimeras, a total of 1212768 high-quality sequences were acquired from all samples. These high-quality sequences were clustered into 7392 OTUs on the basis of 97% similarity. Each sample contained 75798 reads and 462 OTUs on average (see Additional file 1). In this study, six alpha diversity measures were calculated including observied-species (observied OTUs), Shannon, Simpson, Chao1, ACE and PD-whole-tree (see Additional file 2, Additional file 3,Additional file 4 and Additional file 5).
Analysis of the birth canal microbial community of endometritis sows and healthy sows
Under the condition that the similarity was 97%, a total of 1102 OTUs were observed in samples from HV and EV (Fig. 1A). The microbiota of HV and EV samples shared 219 OTUs, with 874 and 9 OTUs uniquely identified from EV and HV samples, respectively (Fig. 1A). Of which, among the 874 OTUs unique to the EV group include 301 bacterial genera, the 9 OTUs unique to the HV group contain 3 bacterial genera, the 219 OTUs shared by EV and HV contain 98 bacteria genera. Different from the analysis of other microfloras, the diversity of HV microfloras was significantly lower than that of EV. In the PCoA figure, both the unweighted UniFrac distance (Fig. 2A) and the weighted UniFrac distance (Fig. 2B) could distinguish the significantly difference in microbiota communities between EV and HV samples (Fig. 2).
Figure 3 showed the average relative abundance of the top 20 phylum and top 30 genus bacteria in the EV and HV samples. At the level of phylum, five predominant phyla were identified in the bacterial communities of EV and HV samples. On average, the relative abundance of these bacteria is over 1%. Firmicutes (41.26%) was the most predominant phyla in EV samples, followed by Proteobacteria (30.47%), Bacteroidetes (17.78%) and Actinobacteria (5.48%) (Fig. 3A). The most dominant bacteria in HV samples were Firmicutes (74.36%) and Proteobacteria (24.68%) (Fig. 3A). The relative abundance of Firmicutes in HV was significantly higher than that of in EV (P < 0.05).Compared with HV samples,the relative abundance of Bacteroidetes, Actinobacteria and Fusobacteria in EV samples were significantly increased (P < 0.05) (see Additional file 6).
A total of 337 genera were identified in the birth canal bacterial communities of endometritis sows compared to 100 genera in healthy sows. In EV samples, the most dominant bacterial genera included Porphyromonas (9.54%), Clostridium_sensu_stricto_1 (6.66%), Streptococcus (6.26%), Vulcaniibacterium (5.88%), Campylobacter (5.24%), Veillonella (3.98%), Escherichia-Shigella (3.84%), Ezakiella (3.74%), Schlegelella (3.59%) and Fusobacterium (3.13%) (Fig. 3B). Lactobacillus (42.84%), Enterococcus (28.04%), Pseudomonas (21.27%), Psychrobacter (3.02%) and Staphylococcus (2.91%) were the dominant genera in HV samples (Fig. 3B). The relative abundance of Clostridium-sensu-stricto-1, Streptococcus, Ezakiella, Fusobacterium, Actinobacillus, Bacteroides, Prevotella and Anaerococcus were significantly higher in EV samples than that of HV sample (P < 0.05) (see Additional file 6). LEfSe (linear discriminant analysis effect size) analysis method was used to detect bacterial taxa of significant difference between EV and HV. The results showed that three bacterial species (Actinobacillus_rossi, Streptococcus_gallolyticus_subsp_macedonicus, and Porphyromonas_somerae) were the significant higher in EV samples compared with HV samples. Lactobacillus_sakei was the significant higher in HV samples compared with EV samples (Fig. 4A and Additional file 6).
The relationship between the birth canal and intestinal flora of endometritis sows
A total of 1115 OTUs were observed in samples from EV and EF (Fig. 1B). The microbiota of EV and EF samples shared 413 OTUs, with 680 and 22 OTUs uniquely identified from EV and EF samples, respectively (Fig. 1B). On the PCoA plot, the unweighted UniFrac distance (Fig. 2A) could completely separate the EV samples from EF samples. However, the weighted UniFrac distance does not completely separate the EV sample from the EF sample (Fig. 2B). This indicates that, to some extent, there is a certain similarity between the birth canal and intestinal flora of endometritis sows. At the levels of phylum, both Proteobacteria and Firmicutes have high relative abundance in EV and EF samples (see Additional file 7).
At the levels of genus, Psychrobacter (23.29%), Pseudomonas (18.38%), Escherichia-Shigella (15.91%), Lactococcus (4.91%), Brochothrix (3.84%), and Bacteroides (1.57%) were other six dominant genera in EF samples (Fig. 3B). In EV samples, Porphyromonas (9.54%), Clostridium_sensu_stricto_1 (6.66%), Streptococcus (6.26%), Vulcaniibacterium (5.88%), Campylobacter (5.24%), Veillonella (3.98%), Escherichia-Shigella (3.84%), Ezakiella (3.74%), Schlegelella (3.59%) and Fusobacterium (3.13%) were the predominant genera (Fig. 3B). It should be noted that both Escherichia-Shigella and Bacteroides were collaborative genera in EF and EV samples.
Difference of intestinal community of healthy sows and endomentritis sows
In the study, a total of 1069 OTUs were observed in samples from HF and EF (Fig. 1C). The microbiota of HF and EF samples shared 251 OTUs, with 634 and 184 OTUs uniquely identified from HF and EF samples, respectively. The community richness index (Chao1 and ACE) and community diversity index (Shannon) were extremely significant higher in HF samples than those of EF samples (P < 0.01) (see Additional file 4), only the Simpson Index difference is not significant (P < 0.05), indicating that both community richness and community diversity were dramatically higher in HF samples than in EF samples. Next, the unweighted UniFrac distance showed remarkable segregations of microbiota between HF samples and EF samples (Fig. 2A). Similar discrimination was also observed, via weighted UniFrac distances, in the PCoA (Fig. 2B), suggesting that the Beta diversity of HF samples were also obvious higher than EF samples.
A total of 165 genera were identified in the intestines bacterial communities of endometritis sows compared to 211 genera in healthy sows. To identify the significant differences in gut bacteria between HF and EF samples, we compared the relative abundance of gut bacteria in HF and EF samples. The result indicated that the relative abundance of six genera (Lactobacillus, Pseudomonas, Psychrobacter, Escherichia-Shigella, Brochothrix and Bacteroides) exhibited obvious increased in the EF samples, although the difference is not significant(see Additional file 8). LEfSe analysis also revealed that Brochothrix_thermosphacta, Lactococcus_raffinolactis, Psychrobacter_faecalis, Pseudomonas_fragi, and Psychrobacter_maritimus were the significant higher in EF samples compared with HF samples (Fig. 4B ).In brief, compared with HV samples,there were 874(238 + 76 + 394 + 166) unique OTUs in EV samples, of which 242(76 + 166)OTU were shared with EF; while among these 242 OTUs, 166 OTUs were shared with HF, and only 76 OTUs were shared with EF. 76 OTUs were the key to understanding the relationship between the occurrence of sow endometritis and its intestinal flora (Fig. 1D).It was found that there were 5 bacterial phylum, mainly including Firmicutes, Bacteroidetes, Actinobacteria, and 46 bacterial genera in 76 OUTs. These bacterial genera including Bacteroides, Peptoniphilus, Flavobacterium, Anaerococcus, etc, among which Bacteroides was the most abundant genus༎