Microbial communities associated with the mature sporophytes and sporelings of the commercially cultivated seaweed Saccharina japonica in Southern China

Epimicrobiota associated with seaweeds are crucial for the health and development of their hosts due to their ability to produce antibiotics, phytohormones and vitamins, etc. However, there is limited knowledge related to the microbiota of commercially cultivated seaweed Saccharina japonica. In this study, we investigated the dynamics of microbiota associated with S. japonica from mature sporophytes to sporelings (usually from September to November) using Illumina sequencing of the V3-V4 hypervariable region of 16S rRNA gene. The composition and structure of epimicrobiota showed significant differences from mature sporophytes to 6-week-old sporelings (pairwise comparison: p < 0.05) and were relatively stable from 7-week-old sporelings to 8-week-old sporelings (pairwise comparison: p > 0.05). Blastopirellula and Pseudoalteromonas were the dominant genera of the community of mature sporophytes and 6-week-old sporelings, respectively. Rubritalea was the most dominant genus for both 7 and 8-week-old sporelings. These three genera were also part of the core microbiota, suggesting that they may play an essential function within the S. japonica holobiont. In addition, members of the Planctomicrobium and Roseibacillus were identified as both drivers (driving the dynamics of adjacent bacterial communities) and keystone taxa (critical for the stability and function of bacterial communities), which might be responsible for the epimicrobiota shifts from 7-week-old sporelings to 8-week-old sporelings and were fundamental for the newly assembled epimicrobiota. This study not only enriches the baseline data related to the microbiota of the commercially farmed S. japonica, but also helps nursery farms to develop techniques for disease control by monitoring the shifts of dominant taxa, core species, indicator species or keystone taxa.