Environmental filtering: A case of bacterial community assembly in soil

Soil has a strong effect on the assembly of bacterial communities, as revealed by studies in which sterilized soil is inoculated with dilution series of bacterial suspensions from the same soil. However, the impact of soil on the assembly of bacterial communities after inoculation with suspensions from different soils is not clear. Here, we explored environmental filtering of bacterial community assembly. Diluted suspensions from different soils harboring different bacterial diversities were used to cross-inoculate three pre-sterilized soils. The main differences in the abiotic factors of the soils were organic matter, ammonium, nitrate, and phosphorus content, pH and the C:N ratio. We used 16S rRNA gene amplicon sequencing to determine the bacterial community structure of the suspensions and the soils. When the different diluted suspensions were used to inoculate their native soils, the regrown soil bacterial communities clustered together; by contrast, the communities were separated when the same suspensions were used to inoculate soils other than their native soils. The diversity indices of the suspensions decreased significantly upon dilution. The strength of selection of bacterial communities by soil was stronger for the 10(-1) diluted soil samples than for the 10(-9) diluted soil samples. Thus, differences in abiotic factors shape and explain the variation in bacterial community assemblage among these soils.