An experimental test of the influence of microbial manipulation on sugar kelp (Saccharina latissima) supports the core influences host function hypothesis

Background

The ability to grow food and resources has become imperative for our expanding population. The cultivation of sugar kelp (Saccharina latissimi) has gained popularity in the Northern Hemisphere as a potential source for biofuels, livestock feed, and as a component of integrated multi-trophic aquaculture. Like most other forms of cultivation, kelp growers experience challenges when it comes to increasing growth and yield, which appear to be linked to microbial communities.

In kelp aquaculture, it is standard practice to remove microbes and reduce microbial growth to limit disease and biofouling pressure. However, these processes also remove beneficial microbes. Recent research highlights the importance of symbiotic bacteria for host development, survival, and overall fitness. With this knowledge, growers have an opportunity to manipulate the microbial environment of kelp during cultivation to potentially increase production while still limiting disease and fouling pressure.

While the microbial community can be quite diverse, it is generally assumed that microbes more consistently associated with sugar kelp, referred to as core bacteria, will have more influence on its functioning. Thus, identifying and manipulating these core bacteria during the cultivation process may be most impactful.

Park et al., (2025) investigated this in the study highlighted here. They began by sampling the sugar kelp microbiome across space and time, and then compared it to the surrounding environment to identify the core microbes. Once identified, these core microbes were isolated and co-cultured with sugar kelp to assess their influence on kelp development. Lastly, the kelp was outplanted at several ocean farms, where development was tracked over a six-month period.

Key Findings

1) The microbiome of wild sugar kelp is different to that of its surrounding environment and cultivated (hatchery and out planted) kelp.

The microbiome composition of wild sugar kelp was significantly different to the microbiome of the surrounding water and rocks. Additionally, the microbiome of wild, nursery, and outplanted cultivated sugar kelp were all significantly different from one another (Fig. 1). However, the core bacteria found on wild kelp were also observed on the outplanted cultivated kelp after 12 months, suggesting that core bacteria can be recruited onto cultivated kelp over time (Fig. 1).

 

2) Culturing sugar kelp with microbes from wild sugar kelp increased development most of the time.

Across all trials, 87% of the bacterial isolates had a significant positive impact on gametophyte coverage and 85% of bacterial isolates had a positive impact on sporophyte number (Fig. 2).

 

3) Bacterial genera more strongly associated with sugar kelp are more likely to increase development.

There was a significantly positive relationship between the strength of association between bacteria with sugar kelp and the number of sporophytes produced as well as gametophyte coverage (Fig. 3).

Why I highlight this preprint

This preprint is well written and reports unique findings that can be implemented to benefit kelp growers. Additionally, the focus on the microbiome I found particularly compelling. While microbiomes are commonly discussed in the context of human health, typically regarding the importance of a balanced gut ecosystem, it is intriguing to see this concept extended to marine organisms like kelp. This broader application highlights the fundamental role microbiomes play across diverse biological systems.

Questions for the authors

1) Was there a consistent relationship between the bacteria isolates that had a negative impact on gametophyte coverage and sporophyte number, and can these be removed for future experimentation?

2) How do the increased sporophyte numbers and gametophyte coverage seen with added microbes in the hatchery compare to those found in wild kelp?

Tags: bacterial isolation, kelp cultivation, microbial ecology, microbial manipulation, saccharina latissima

doi: https://doi.org/10.1242/prelights.40201

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