# Effects of the tidal dehydration stress on epiphytic bacterial community of the intertidal macroalga Sargassum thunbergii

## TL;DR

This study explores how tidal dehydration affects the bacterial community living on a type of seaweed, revealing changes in diversity and function.

## Contribution

The study reveals how dehydration stress alters both structure and function of epiphytic bacterial communities on intertidal macroalgae.

## Key findings

- Tidal dehydration significantly alters community diversity and abundance of dominant bacterial taxa.
- Dehydration stress induces metabolic reprogramming in energy, nitrogen, and sulfur cycling pathways.
- Stress-tolerant bacterial taxa are selectively enriched under dehydration stress.

## Abstract

Intertidal macroalgae and their epiphytic bacteria experience periodic dehydration-rehydration cycles due to tidal fluctuations. The influence of tidal dehydration on algal epiphytic bacteria remains poorly understood. This study investigated the effect of tidal dehydration on epiphytic bacterial communities of macroalga Sargassum thunbergii. While tidal dehydration had a small impact on the composition of the epiphytic bacterial community of S. thunbergii, it significantly influenced community diversity, abundance of dominant taxa, and some predicted functional genes. Specifically, the abundance of Proteobacteria and Granulosicoccus increased markedly, whereas that of Cyanobacteria, Litoreibacter, and Sva0996_marine_group decreased significantly. The abundance of Marinomonas exhibited a trend of initial decrease, followed by subsequent increase. Predictive functional analysis suggested that the bacterial community adapted to dehydration stress by regulating genes involved in energy, nitrogen, and sulfur metabolism. The shifts in the bacterial community following dehydration stress may result from the inherent differential stress tolerance among bacterial taxa and host-mediated facilitation through algal metabolic adjustments that selectively favored specific groups. This study revealed the structural and functional response of the epiphytic bacterial community of macroalgae in intertidal zones to dehydration stress.

The adaptive mechanisms of the intertidal macroalgal-epiphytic bacterial symbiotic system to periodic tidal dehydration stress play a crucial role in maintaining coastal ecosystem stability. Although numerous studies have investigated the effects of tidal dehydration on intertidal macroalgae, the impact of dehydration on the epiphytic bacteria has received much less attention. Our investigation revealed that tidal dehydration stress significantly alters both the community structure and metabolic functions of the epiphytic bacteria on Sargassum thunbergii. Notably, dehydration stress selectively enriched stress-tolerant bacterial taxa and induced metabolic reprogramming, particularly in energy, nitrogen, and sulfur cycling pathways. These microbial responses demonstrate not only bacterial stress adaptation strategies but also suggest potential host-mediated regulation within the algal-bacterial symbiotic system. These findings provide novel insights into the ecological adaptability mechanisms of intertidal ecosystems under environmental stress.