4.2 Effects of different dietary protein levels on intestinal microflora structure and KEGG functional predictions
Analyzing the structural composition of animal intestinal microbes can reflect growth environments and diet to a certain extent [25]. In one study, Zhou et al. [26] found that low-protein diets can regulate microbial composition and metabolites in pig hindguts without influencing growth performance although the potential effects of this regulation on health remains unknown. Here, microbes in the jejunum and cecum of Bamei pig were mainly shown to comprise representatives of phyla Firmicutes and Bacteroidetes, although significant differences were seen between groups at different protein levels. Representatives of phylum Firmicutes in jejunum test group II samples occurred at significantly higher proportions than those in test group I samples (P = 0.020). Similarly, representatives of phylum Firmicutes in caecum test group II samples also occurred at significantly higher levels than in test group I (P = 0.034) while representatives of phylum Bacteroidetes in test group I samples also occurred at significantly higher levels than in test group II samples (P = 0.011). These outcomes show that reducing the protein level can have an effect on the structure of the main flora of the phylum level. Indeed, Firmicutes is also the dominant intestinal phylum present in the low protein group, consistent with previous studies [13,27]. Dai et al [28] showed that, at the genus level, bacteria in the jejunum of Bamei pigs mainly comprise unidentified Clostridiales ,Terrisporobacter , and Turicibacter , while those in the cecum mainly include unidentified Clostridiales ,Terrisporobacter , Turicibacter , and Streptococcus . The main role of Streptococcus appears to be to utilize AA in the intestine to synthesize bacterial proteins. In another earlier study, Fan et al. [20] showed that as dietary protein levels decrease, the abundance of Clostridium sensu stricto 1 in ileum samples from pigs decreased significantly. The reason for the analysis is that a decrease in dietary protein level causes a reduction in nitrogen source as a fermentation substrate. The relative abundances ofTerrisporobacter in the diet group with a normal protein level were also significantly higher than in the group fed a low protein level; this genus is an emerging anaerobic pathogen but the few cases published so far usually report it as a component of a multi-microbial infection [29]. Similarly, Romboutsia occurred at a higher level in the normal diet protein group than the low protein group. The results of this study show that as dietary protein levels decrease, the proportion of Lactobacillus in jejunum and cecum of microbial floras also gradually increased. Dietary protein levels therefore exert a certain influence on the composition of Bamei pig intestinal floras. As dietary protein levels decrease, no significant differences in abundance either the jejunum or caecum were seen although this change can improve microbial composition. The outcomes of this study have also enabled us to predict the KEGG functions of genes present in microbial floras at different dietary protein levels. These results show that genes extracted from jejunum and cecum microbes at different dietary protein levels were mainly enriched in the ‘metabolism pathway’, followed by ‘genetic-information-processing’, and ‘environmental-information-processing’ channels. In contrast, at Level2, the main enrichment pathways are ‘membrane-transport’ and ‘carbohydrate-metabolism’. Enrichment pathways in jejunum and cecum genes are significantly different in terms of the presence of ‘metabolism’ and ‘environmental-information-processing’; these results indicate that an appropriate reduction in dietary protein can have a beneficial effect on the metabolic function of microorganisms in the intestine. A reduction can assist metabolic activities, consistent with previous work [30–31].