Effects of Chlorella and Spirulina on bacterial community composition in a dual-flow continuous culture system

The objective of this study was to evaluate the partial replacement of soybean meal (SBM) with either Chlorella pyrenoidosa or Spirulina platensis in a high producing dairy cow diet on ruminal bacterial communities. A dual-flow continuous culture system was used in a replicated 3 × 3 Latin Square design. A control diet (CRT) with SBM at 17.8% DM; and 50% SBM biomass replacement with either Chlorella pyrenoidosa (CHL); or Spirulina platensis (SPI). All diets were formulated to provide 16.0% CP, 34.9% NDF, 31.0% starch DM basis. Samples were collected from the fluid and solid effluents at 3, 6, and 9 h after feeding; a composite of all time points was made for each fermenter within their respective fractions. Treatment responses for bacterial community structure were analyzed with the PERMANOVA test run with the R Vegan package. Orthogonal contrasts were used to test the effects of 1) partial replacement of SBM with algae (CRT vs. CHL, and SPI); and 2) the comparison of algae sources (CHL vs. SPI). The orthogonal contrasts were used to test the effects of the treatments on phylum, family, and genus differential abundance using the R limma package. The relative abundance of Ruminobacter in liquid fraction was greater for CHL and SPI than CRT, while the relative abundance of Butyrivibrio, and Pseudobutyrivibrio in solid fraction were lower for CHL and SPI compared to CRT, respectively. Moreover, the relative abundance of Ruminobacter in liquid fraction was greater for CHL compared to SPI. Our results demonstrate that Chlorella and Spirulina supplementation enhance the abundance of bacteria associated with propionate production in the rumen.