Characterization and comparison of bacterial communities of an invasive and two native Caribbean seagrass species sheds light on the possible influence of the microbiome on invasive mechanisms

Invasive plants, including marine macrophytes, are one of the most important threats to biodiversity by displacing native species and organisms depending on them. Invasion success is dependent on interactions among living organisms, but their study has been mostly limited to negative interactions while positive interactions are mostly underlooked. Recent studies suggested that microorganisms associated with eukaryotic hosts may play a determinant role in the invasion process. Along with the knowledge of their structure, taxonomic composition, and potential functional profile, understanding how bacterial communities are associated with the invasive species and the threatened natives (species-specific/environmentally shaped/tissue-specific) can give us a holistic insight into the invasion mechanisms. Here, we aimed to compare the bacterial communities associated with leaves and roots of two native Caribbean seagrasses (Halodule wrightii and Thalassia testudinum) with those of the successful invader Halophila stipulacea, in the Caribbean island Curaçao, using 16S rRNA gene amplicon sequencing and functional prediction. Invasive seagrass microbiomes were more diverse and included three times more species-specific core OTUs than the natives. Associated bacterial communities were seagrass-specific, with higher similarities between natives than between invasive and native seagrasses for both communities associated with leaves and roots, despite their strong tissue differentiation. However, with a higher number of OTUs in common, the core community (i.e., OTUs occurring in at least 80% of the samples) of the native H. wrightii was more similar to that of the invader H. stipulacea than T. testudinum, which could reflect more similar essential needs (e.g., nutritional, adaptive, and physiological) between native and invasive, in contrast to the two natives that might share more environment-related OTUs. Relative to native seagrass species, the invasive H. stipulacea was enriched in halotolerant bacterial genera with plant growth-promoting properties (like Halomonas sp. and Lysinibacillus sp.) and other potential beneficial effects for hosts (e.g., heavy metal detoxifiers and quorum sensing inhibitors). Predicted functional profiles also revealed some advantageous traits on the invasive species such as detoxification pathways, protection against pathogens, and stress tolerance. Despite the predictive nature of our findings concerning the functional potential of the bacteria, this investigation provides novel and important insights into native vs. invasive seagrasses microbiome. We demonstrated that the bacterial community associated with the invasive seagrass H. stipulacea is different from native seagrasses, including some potentially beneficial bacteria, suggesting the importance of considering the microbiome dynamics as a possible and important influencing factor in the colonization of non-indigenous species. We suggest further comparison of H. stipulacea microbiome from its native range with that from both the Mediterranean and Caribbean habitats where this species has a contrasting invasion success. Also, our new findings open doors to a more in-depth investigation combining meta-omics with bacterial manipulation experiments in order to confirm any functional advantage in the microbiome of this invasive seagrass.CEECINST/00114/2018info:eu-repo/semantics/publishedVersio

High diversity of benthic cyanobacterial mats on coral reefs of Koh Tao, Gulf of Thailand

Benthic cyanobacterial mats are increasingly reported to cover major coral reef areas. Although suggestions have been made that cyanobacterial mats impair coral reef health in multiple ways, information is lacking regarding the distribution, morphotypical variation and bacterial species composition of these microbial mats. As such, this study aimed to (1) Reveal the bacterial community diversity and composition of different mat morphotypes, (2) Identify the most abundant community members and closely related organisms, (3) Assess to what extent, morphotype, colonized substrate (coral or abiotic substrate), depth, and site were significant predictors of bacterial composition. Data were collected on reefs surrounding the island of Koh Tao (Gulf of Thailand). A total of 201 mats from 16 different locations around the island were classified into eight distinct morphotypes. Of these, the bacterial communities of 44 mats, representing colour groups from multiple sites, were characterized using 16S rRNA gene high-throughput sequencing. Our data revealed that Proteobacteria, Cyanobacteria, Bacteriodetes and Planctomycetes were the four most abundant phyla and occurred in all samples. Abundant cyanobacterial zero-radius operational taxonomic units (ZOTUs) were closely related to prokaryotic sequences found in previous studies of coastal mats (98–100%) and were assigned to genera in the order Oscillatoriales, e.g. Hormoscilla, Okeania, and Oscillatoria. Abundant proteobacterial ZOTUs were assigned to orders in the classes Alpha- and Gammaproteobacteria, e.g. Rhodobacterales, Rhizobiales and Alteromonadales. Abundant Bacteriodetes ZOTUs were mainly assigned to the class Bacteroidia and order Cytophagales. Our results showed that mats consist of a diverse and variable bacterial consortium, with mat colour (morphotype), substrate type and geographic location only explaining a small part of the total variation in composition

High diversity of benthic cyanobacterial mats on coral reefs of Koh Tao, Gulf of Thailand

Benthic cyanobacterial mats are increasingly reported to cover major coral reef areas. Although suggestions have been made that cyanobacterial mats impair coral reef health in multiple ways, information is lacking regarding the distribution, morphotypical variation and bacterial species composition of these microbial mats. As such, this study aimed to (1) Reveal the bacterial community diversity and composition of different mat morphotypes, (2) Identify the most abundant community members and closely related organisms, (3) Assess to what extent, morphotype, colonized substrate (coral or abiotic substrate), depth, and site were significant predictors of bacterial composition. Data were collected on reefs surrounding the island of Koh Tao (Gulf of Thailand). A total of 201 mats from 16 different locations around the island were classified into eight distinct morphotypes. Of these, the bacterial communities of 44 mats, representing colour groups from multiple sites, were characterized using 16S rRNA gene high-throughput sequencing. Our data revealed that Proteobacteria, Cyanobacteria, Bacteriodetes and Planctomycetes were the four most abundant phyla and occurred in all samples. Abundant cyanobacterial zero-radius operational taxonomic units (ZOTUs) were closely related to prokaryotic sequences found in previous studies of coastal mats (98–100%) and were assigned to genera in the order Oscillatoriales, e.g. Hormoscilla, Okeania, and Oscillatoria. Abundant proteobacterial ZOTUs were assigned to orders in the classes Alpha- and Gammaproteobacteria, e.g. Rhodobacterales, Rhizobiales and Alteromonadales. Abundant Bacteriodetes ZOTUs were mainly assigned to the class Bacteroidia and order Cytophagales. Our results showed that mats consist of a diverse and variable bacterial consortium, with mat colour (morphotype), substrate type and geographic location only explaining a small part of the total variation in composition