Host differentially expressed genes during association with its defensive endosymbiont

Long-read sequencing reveals the shell microbiome of apparently healthy American lobsters Homarus americanus from Atlantic Canada

The shell microbial community of lobsters-a key factor in the development of epizootic shell disease (ESD)-is still insufficiently researched in Atlantic Canada and many knowledge gaps remain. This study aimed to establish a baseline description and analysis of the shell microbiome of apparently healthy lobsters from four locations in the region. More than 180 lobster shell swab samples were collected from New Brunswick, Nova Scotia and Prince Edward Island (PEI). PacBio long-read 16S rDNA sequencing and bioinformatic analyses in QIIME2 identified the shell-associated bacteria. The shell microbiome of healthy lobsters consisted mainly of the bacterial classes Gammaproteobacteria, Saprospiria, Verrucomicrobiae, Alphaproteobacteria, Flavobacteriia, Acidimicrobiia and Planctomycetia. The microbial composition differed regionally and seasonally, with some classes showing decreased or increased relative abundances in the PEI samples as well as in the winter and spring samples in Nova Scotia. The core shell microbiome included potentially pathogenic as well as beneficial bacterial taxa, of which some were present only in certain regions. Bacterial taxa that have previously been associated with ESD were present on healthy lobsters in Atlantic Canada, but their frequency differed by location, sampling time, and moult stage. This study indicated that geographical and seasonal factors influenced the shell microbiome of apparently healthy lobsters more than host factors such as sex, size, and moult stage. Our results provide valuable reference microbial data from lobsters in a disease-free state.

Impact of Marine Chemical Ecology Research on the Discovery and Development of New Pharmaceuticals

Diverse ecologically important metabolites, such as allelochemicals, infochemicals and volatile organic chemicals, are involved in marine organismal interactions. Chemically mediated interactions between intra- and interspecific organisms can have a significant impact on community organization, population structure and ecosystem functioning. Advances in analytical techniques, microscopy and genomics are providing insights on the chemistry and functional roles of the metabolites involved in such interactions. This review highlights the targeted translational value of several marine chemical ecology-driven research studies and their impact on the sustainable discovery of novel therapeutic agents. These chemical ecology-based approaches include activated defense, allelochemicals arising from organismal interactions, spatio-temporal variations of allelochemicals and phylogeny-based approaches. In addition, innovative analytical techniques used in the mapping of surface metabolites as well as in metabolite translocation within marine holobionts are summarized. Chemical information related to the maintenance of the marine symbioses and biosyntheses of specialized compounds can be harnessed for biomedical applications, particularly in microbial fermentation and compound production. Furthermore, the impact of climate change on the chemical ecology of marine organisms-especially on the production, functionality and perception of allelochemicals-and its implications on drug discovery efforts will be presented.

Differential Gene Expression Between Polymorphic Zooids of the Marine Bryozoan Bugulina stolonifera

Bryozoans are a diverse phylum of marine and freshwater colonial invertebrates containing approximately 6,300 described living species. Bryozoans grow by budding new physiologically connected colony members (zooids) from a founding individual that forms from a metamorphosed larva. In some species these zooids come in different shapes and sizes and are specialized to serve different tasks within the colony. A complex interaction of genotype, environment, and developmental pathway shapes zooid fate, however, the specific mechanisms underlying the establishment of this division of labor remain unknown. Here, the first characterization of differential gene expression between polymorphic zooids of a bryozoan colony is presented. The development of different zooid types of lab-cultured Bugulina stolonifera colonies including feeding autozooids, avicularia (derived non-feeding zooids that are homologous to feeding autozooids but shaped like a bird's beak), and rhizoids (a branching network of non-feeding anchoring zooids) was explored using RNA sequencing, de novo transcriptome assembly, and differential gene expression analyses. High throughput sequencing of cDNA libraries yielded an average of 14.9 ± 1.3 (SE) million high-quality paired-end reads per sample. Data for the first de novo transcriptome assemblies of B. stolonifera and the first characterization of genes involved in the formation and maintenance of zooid types within a bryozoan colony are presented. In a comparison between autozooid and avicularium tissues, 1,097 significant differentially expressed genes were uncovered. This work provides a much-needed foundation for understanding the mechanisms involved in the development of polymorphic zooids and the establishment of division of labor in bryozoans.

Diversity and Dynamics of "Candidatus Endobugula" and Other Symbiotic Bacteria in Chinese Populations of the Bryozoan, Bugula neritina

Bugula neritina is a common invasive cosmopolitan bryozoan that harbors (like many sessile marine invertebrates) a symbiotic bacterial (SB) community. Among the SB of B. neritina, "Candidatus Endobugula sertula" continues to receive the greatest attention, because it is the source of bryostatins. The bryostatins are potent bioactive polyketides, which have been investigated for their therapeutic potential to treat various cancers, Alzheimer's disease, and AIDS. In this study, we compare the metagenomics sequences for the 16S ribosomal RNA gene of the SB communities from different geographic and life cycle samples of Chinese B. neritina. Using a variety of approaches for estimating alpha/beta diversity and taxonomic abundance, we find that the SB communities vary geographically with invertebrate and fish mariculture and with latitude and environmental temperature. During the B. neritina life cycle, we find that the diversity and taxonomic abundances of the SB communities change with the onset of host metamorphosis, filter feeding, colony formation, reproduction, and increased bryostatin production. "Ca. Endobugula sertula" is confirmed as the symbiont of the Chinese "Ca. Endobugula"/B. neritina symbiosis. Our study extends our knowledge about B. neritina symbiosis from the New to the Old World and offers new insights into the environmental and life cycle factors that can influence its SB communities, "Ca. Endobugula," and bryostatins more globally.

An interdomain network: the endobacterium of a mycorrhizal fungus promotes antioxidative responses in both fungal and plant hosts

Arbuscular mycorrhizal fungi (AMF) are obligate plant biotrophs that may contain endobacteria in their cytoplasm. Genome sequencing of Candidatus Glomeribacter gigasporarum revealed a reduced genome and dependence on the fungal host. RNA-seq analysis of the AMF Gigaspora margarita in the presence and absence of the endobacterium indicated that endobacteria have an important role in the fungal pre-symbiotic phase by enhancing fungal bioenergetic capacity. To improve the understanding of fungal-endobacterial interactions, iTRAQ (isobaric tags for relative and absolute quantification) quantitative proteomics was used to identify differentially expressed proteins in G. margarita germinating spores with endobacteria (B+), without endobacteria in the cured line (B-) and after application of the synthetic strigolactone GR24. Proteomic, transcriptomic and biochemical data identified several fungal and bacterial proteins involved in interspecies interactions. Endobacteria influenced fungal growth, calcium signalling and metabolism. The greatest effects were on fungal primary metabolism and respiration, which was 50% higher in B+ than in B-. A shift towards pentose phosphate metabolism was detected in B-. Quantification of carbonylated proteins indicated that the B- line had higher oxidative stress levels, which were also observed in two host plants. This study shows that endobacteria generate a complex interdomain network that affects AMF and fungal-plant interactions.

Latitudinal variation of a defensive symbiosis in the Bugula neritina (Bryozoa) sibling species complex

Mutualistic relationships are beneficial for both partners and are often studied within a single environment. However, when the range of the partners is large, geographical differences in selective pressure may shift the relationship outcome from positive to negative. The marine bryozoan Bugula neritina is a colonial invertebrate common in temperate waters worldwide. It is the source of bioactive polyketide metabolites, the bryostatins. Evidence suggests that an uncultured vertically transmitted symbiont, "Candidatus Endobugula sertula", hosted by B. neritina produces the bryostatins, which protect the vulnerable larvae from predation. Studies of B. neritina along the North American Atlantic coast revealed a complex of two morphologically similar sibling species separated by an apparent biogeographic barrier: the Type S sibling species was found below Cape Hatteras, North Carolina, while Type N was found above. Interestingly, the Type N colonies lack "Ca. Endobugula sertula" and, subsequently, defensive bryostatins; their documented northern distribution was consistent with traditional biogeographical paradigms of latitudinal variation in predation pressure. Upon further sampling of B. neritina populations, we found that both host types occur in wider distribution, with Type N colonies living south of Cape Hatteras, and Type S to the north. Distribution of the symbiont, however, was not restricted to Type S hosts. Genetic and microscopic evidence demonstrates the presence of the symbiont in some Type N colonies, and larvae from these colonies are endowed with defensive bryostatins and contain "Ca. Endobugula sertula". Molecular analysis of the symbiont from Type N colonies suggests an evolutionarily recent acquisition, which is remarkable for a symbiont thought to be transmitted only vertically. Furthermore, most Type S colonies found at higher latitudes lack the symbiont, suggesting that this host-symbiont relationship is more flexible than previously thought. Our data suggest that the symbiont, but not the host, is restricted by biogeographical boundaries.