Abstract: To study the effect of different pre-filtering pore-size on planktonic bacterial community compositions (BCCs), BCCs collected by three filtering methods (10 μm pre-filtering, 2 μm pre-filtering, and without pre-filtering) were compared through high-throughput sequencing. The result showed that BCCs were similar between 10 μm pre-filtering (PF10) and 2 μm pre-filtering (PF2), while they were significantly different with those without filtering (PF100). The alpha diversity of PF100 samples was the highest among all the treatments. Compared with PF10 and PF2, the relative abundances of Chloroflexi, Planctomycetes, Verrucomicrobia and Cyanobacteria were significantly higher in PF100 samples (P < 0.05), while those of Alphaproteobacteria, GN02 and OD1 were lower. Similarity percentage (SIMPER) analysis indicated that 12 families cumulatively contributed to 63.45% dissimilarity of the BCCs. In conclusion, the different pre-filtering pore-size could induce the bias of planktonic bacterial community structure. The results have an important guiding significance in selecting the planktonic bacteria filtration method.

Key words: pre-filtering, bacterioplankton, community composition, particle-attached bacteria, free-living bacteria