Microbiota-Macroalgal Relationships at a Hawaiian Intertidal Bench Are Influenced by Macroalgal Phyla and Associated Thallus Complexity

Functional prediction based on 16S rRNA metagenome data from bacterial microbiota associated with macroalgae from the Peruvian coast

Macroalgae are vital reservoirs for essential epibiotic microorganisms. Among these are growth-promoting bacteria that support the growth and healthy development of their host macroalgae, and these macroalgae can be utilized in agriculture as biostimulants, offering an alternative to traditional agrochemicals. However, to date, no comparative studies have been conducted on the functional profile and bacterial diversity associated with coastal macroalgae of Peru. In this study, we employed amplicon sequencing of the V3-V4 region of 16S rRNA gene in twelve host macroalgae collected from two rocky shores in central Peru to compare their bacterial communities. The results revealed high bacterial diversity across both sites, but differences in microbial composition were noted. The phyla Bacteroidota and Pseudomonadota were predominant. The functional prediction highlighted 44 significant metabolic pathways associated with the bacterial microbiota when comparing host macroalgae. These active pathways are related to metabolism and genetic and cellular information processing. No direct association was detected between the macroalgal genera and the associated microbiota, suggesting that the bacterial community is largely influenced by their genetic functions than the taxonomic composition of their hosts. Furthermore, some species of Chlorophyta and Rhodophyta were observed to host growth-promoting bacteria, such as Maribacter sp. and Sulfitobacter sp.

Water depth outweighs reef condition in shaping non-geniculate coralline algae-associated microbial communities in coral reefs: A case study from Thailand

Red calcified non-geniculate coralline algae (NGCA) provide habitat structures, stabilize reef structures, and foster coral larval settlement and metamorphosis. Moreover, the microbes associated with NGCA are dependent on the NGCA host species and are affected by environmental factors; however, little is known about the influence of reef conditions and depth gradients on the associated microbial communities and NGCA. In this study, we collected NGCA under different reef conditions and depth gradients and characterized the microbial communities using the V3-V4 hypervariable regions of the 16S rRNA gene. Metagenomic analysis revealed 2 domains, 51 phyla, 123 classes, and 210 genera. The NGCA-associated bacterial communities were dominated by Proteobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, and Acidobacteriota. Gammaproteobacteria and Alphaproteobacteria were the most abundant bacterial classes. Differences in microbial diversity and richness were not apparent between reef conditions and depth gradients. However, there was a significant difference in bacterial evenness among the depth gradients. The bacterial abundance associated with NGCA was greater in deep zones than in shallow zones. The shallow zone exhibited a greater relative abundance of all gene functions than the deep zone, indicating differences in the distribution of gene functions. This study showed that the microbial communities associated with red calcified NGCA are diverse, and that the depth gradient affects their abundance and evenness, highlighting the need for further research to understand the functional roles of these microbial communities in coral reef conservation.

Characterization of macroalgal-associated microbial communities from shallow to mesophotic depths at Manawai, Papahānaumokuākea Marine National Monument, Hawai'i

The Papahānaumokuākea Marine National Monument, Hawai'i, is one of the most isolated and protected archipelagos in the world, making it a natural laboratory to examine macroalgal-microbial diversity because of limited direct anthropogenic impacts. We collected the most abundant macroalgae from nine sites ranging from shallow subtidal (1.5 m) to mesophotic (75 m) depths around Manawai (Pearl and Hermes Atoll). We characterized the macroalgal bacterial communities via high-throughput amplicon sequencing and compared the influence of host phylum, species, site, and depth on these relationships at a single atoll. Ochrophyta species had the lowest bacterial diversity compared to Chlorophyta and Rhodophyta. Site and/or depth may influence the microbial community structure associated with Microdictyon setchellianum, indicating a possible disconnect of these microbial communities among habitats. Chondria tumulosa, a cryptogenic species with invasive traits, differed in associated microbiota compared to the native Laurencia galtsoffii, an alga from the same family collected at the same site and depth. While there was overlap of bacterial communities across sites for some algal species, the majority had minimal macroalgal-microbial community connectivity across Manawai. This mesophotic system, therefore, did not appear to be refugia for shallow water coral reefs at microscopic scales. Additional studies are required to identify other significant influences on microbial community variation.