Deciphering the seagrass microbiome for advanced ecosystem restoration

Abstract

Seagrasses are important stores of blue carbon and provide important ecosystem services such supporting commercially important fish populations and reducing effects of pollution and erosion; however, seagrasses are in decline because of anthropogenic activities and climate change. Like terrestrial plants, seagrasses depend on mutualistic relationships with bacteria that are central to their health.The purpose of this study was to investigate the effect of bacteria on seagrass germination with the overall prospect of utilizing them as probiotics for seagrass restoration.Seagrass seeds and sediment samples were collected from a restoration nursery in Carmarthenshire, UK. Bacterial strains were isolated from the seeds and sediment using a combination of marine broth and F/2-based growth media to capture diverse taxa. Representative colonies were restreaked, and identified by 16S rRNA gene sequencing, then preserved as cryostocks for subsequent experiments.A laboratory-based germination assay was established to test the effects of different substrates (sediment, agar, and sterile seawater) on germination success.Of the three media, agar yielded the highest germination at 36.1% (p = 0.3402).Co-cultivation experiments demonstrated that some bacterial isolates reduced seed mortality, accelerated germination, and promoted seedling growth. For example, Variovorax paradoxus treatments resulted in higher cotyledon length (15 mm ± 7 mm) compared to the control (14.3 mm ± 8.7 mm). However, the results of statistical analysis did not yield a significance in these effects.Furthermore, bioinformatic analyses were utilized to identify relevant pathways in the bacterial genomes including secondary metabolites to further understand the relationship they may have with seagrass.The four analyzed bacteria genomes were found to encode for enzymes that break down cell wall components, which are vital for cycling nutrients that are important for seagrass growth. Biosynthetic gene clusters for secondary metabolites were identified in the genomes that have functions in antifouling, and communication (terpenes) that positively influence seagrass health and growth.This study shows the importance of seagrass associated bacteria to health and growth of seedlings and adult plants. Furthermore, it provides evidence that strains such as V. paradoxus can be used in biofertilizers to enhance conservation of the seagrass ecosystem