Effects of microflora source and liquid volume on corn stover degradation
The results showed that the degradation rate of corn stover was significantly affected by liquid volume but not microflora source (Fig. 1D-F). The degradation rate of 200 mL liquid volume (L2) was significantly higher than that of 100 mL (L1) (Fig. 1F). The degradation rate of L2 was increased by 49% compared with L1, reaching 67.41% (Fig. 1F). The best degradation treatment was Y3, for which the degradation rate was 71.59% (Fig. 1D).
Effects of microflora source and liquid volume on cellulase activities
Endo-glucanase activity was significantly affected by liquid volume but not microflora source (Fig. 1G-I). The endo-glucanase of L2 was significantly increased by 2-fold compared with L1, reaching 3.98 U/ml (Fig. 1I). Pearson correlation results showed that there was a significant correlation between degradation rate and endo-glucanase activity (Table 2).
Table 2
Pearson correlations of degradation ratio with cellulose activity and microbial diversity
|
|
Endoglucanase activity
|
Bacterial alpha diversity
|
Fungal alpha diversity
|
Degradation rata
|
Pearson correlations
|
0.676
|
0.136
|
-0.422
|
Significant
|
0.046
|
0.728
|
0.258
|
Effects of microflora source and liquid volume on microbial diversity
Across all samples, we obtained high-quality bacterial (60,162–69,939 sequences per sample, total = 590,998, mean = 65,666) and fungal sequences (53,598–69,121 sequences per sample, total = 564,656, mean = 62,740). After rarefied to 49,000 sequences per sample, microbial diversity and abundance were calculated. The α-diversity of bacteria and fungi was significantly affected by different microflora sources (Fig. 2). The bacterial Shannon index of Q and Y was significantly higher than that of M. The fungal Shannon index of M was significantly lower than that of Q. Liquid volume had no significant effect on microbial α-diversity. Pearson correlation results showed that there was no significant correlation between degradation rate and microbial α-diversity (Table 2). The results of PCoA and PERMAVONA showed that there were significant differences in bacterial and fungal communities of different microflora sources (Fig. 3A and Fig. 3C). The bacterial and fungal communities were not significantly affected by different liquid volumes (Fig. 3B and Fig. 3D).
Effects of microflora source and liquid volume on microbial composition
Firmicutes and Proteobacteria were the dominant bacterial phyla across all treatments (Fig. 4A). The top 5 bacterial species in M were Brevibacillus borstelensis, uncultured_Clostridia_WSC-8, uncultured_Ruminiclostridium_1, uncultured_ Paenibacillus, and uncultured_o_MBA03. The top 5 bacterial species in Q were uncultured_o_MBA03, uncultured_Hydrogenispora, uncultured_Limnochordaceae, uncultured_Methylococcaceae, and uncultured_Ruminococcaceae_UCG-012. The top 5 species genera in Y were uncultured_o_MBA03, uncultured_Chelativorans, uncultured_Methylococcaceae, uncultured_Hydrogenispora, and uncultured_Haloplasma (Fig. 4B). Unclassified, Ascomycota, Basidiomycota, and Mortierellomycota were the dominant fungal phyla across all treatments (Fig. 4C). The top 5 fungal species in M were Unclassified, Alternaria alternata, Fusarium solani, Mortierella alpine, and Malassezia restricta. The top 5 fungal species in Q were Unclassified, Mortierella elongata, Mortierella alpina, Alternaria alternata, and Hyphoderma setigerum. The top 5 fungal species in Y were Unclassified, Alternaria alternata, Nigrospora oryzae, Epicoccum nigrum, and Zopfiella marina (Fig. 4D).
Effects of microflora source and liquid volume on microbial taxa
LEfSe analysis showed that different microflora sources had significant effects on bacterial taxa (Fig. 5A). M enriched some bacterial taxa from Paenibacillus, Clostridiaceae_1, Ruminiclostridium_1, and M55_D21. Q enriched some bacterial taxa from Deinococcales, Sinibacillus, Heliobacteriaceae, Thermoanaerobacterales, Limnochordales, and uncultured_bacterium_p_Firmicutes. Y enriched some bacterial taxa from Dysgonomonadaceae, Thermobacillus, Caldicoprobacteraceae, Christensenellaceae, Clostridium_sensu_stricto_10, Family_XI, Ruminococcaceae_UCG_010, Ruminococcaceae_UCG_013, D8A_2, uncultured_S0134, Rhizobiales, uncultured_Alphaproteobacteria, Myxococcales, CCD24, and Izimaplasmatales. There were a few differences in bacterial taxa between different liquid volumes (Fig. 5B). L1 enriched 15 bacterial species from Gemella, XI, Granulicateriaceae, Streptococcaceae, Lactobacillales, Massilia, and Neisseriaceae. Different microflora sources had an effect on fungal taxa (Fig. 5C). Q enriched 44 fungal taxa from Botryosphaeriales, Periconiaceae, Phaeosphaeriaceae, Alternaria chlamydosporigena, Chaetothyriales, Gymnoascaceae, Helotiaceae, Pseudaleuria, Saccharomycetes, Fusarium brachygibbosum, Chaetomium iranianum, Microdochium trichocladiopsis, Ceratobasidium, Clavulinaceae, Geastrales, Polyporales, Russulales, Thelephorales, Chytridiomycota, Mortierella amoeboidea, and Mortierella hyalina. There was no significant difference in fungal taxa between different liquid volumes (Fig. 5D)