Comparative study on the community structure of epiphytic bacteria in sporophyte and gametophyte stages of kelp Saccharina japonica

Abstract:

To explore the community structure of epiphytic bacteria on the sporophytes and gametophytes of kelp Saccharina japonica, sequences of 16S rRNA of epiphytic bacteria found on the mature leafy sporophytes (S1), filamentous gametophytes (S2), sporelings (S3), and big leafy sporophytes (S4) were analyzed using Illumina sequencing technology. The results showed that 23 phyla, 156 genera, and 244 kinds of OTUs (Operational Taxonomic Units) were identified in these samples. At the phylum level, Proteobacteria showed higher abundance, with relative abundances of 53.0%, 94.3%, 77.2%, and 36.7% in S1, S2, S3, and S4 samples, respectively. Cyanobacteria showed higher abundance of 43.8% in S4 samples only. At the genus level, the relative abundances of Pseudoalteromonas in S2, S3, and S4 were 65.00%, 44.88%, and 25.57%, respectively, but only 0.18% in S1. The community structure of epiphytic bacteria varied greatly among samples. S1 and S4 samples were clustered together, but S2 and S3 samples were clustered in another branch. The species of the bacteria in S2 samples were single and unevenly distributed. S1, S3, and S4 samples were rich in bacteria, while the relative abundance between different bacteria in S4 samples varied greatly compared to that in other samples. This study revealed that there was an increasing trend in the abundance of alginic acid-degrading bacteria during the breeding stage of S. japonica (S2, and S3), and there was a high abundance of symbiotic Cyanobacteria in the big leafy sporophyte stage (S4).