Composition of Epiphytic Microbial Communities in Gametophytes and Sporophytes of Undaria pinnatifida

Undaria pinnatifida is a brown alga with high economic value. Its annual production is second only to Saccharina japonica among economically important brown algae in China. Due to climate change and increased cultivation density, the occurrence of diseases in cultivated seaweeds has become more frequent and serious in recent years. Most diseases are directly or indirectly related to the interactions between the seaweed host and the epiphytic microorganisms such as bacteria. There is a close relationship between algae and epiphytic microorganisms. When the phycosphere niche maintains a dynamic balance, the two rely positively on each other growing and developing together. When the balance is disturbed, the structure of the epiphytic microbial community may change, possibly resulting in algal diseases. The absence of certain microbes may also lead to the failure of key biological processes such as the morphogenesis of the host algae. Therefore, understanding the composition of the epiphytic microbial community is of great significance for the study of the interaction between U. pinnatifida and epiphytic microorganisms and the better control of U. pinnatifida diseases. In addition, stock resources of U. pinnatifida are usually conserved in the form of gametophytes, which can persist for a long time under controlled conditions. Hence, understanding the composition of the epiphytic microbial community will also facilitate the development of efficient conservation methods and help remove microbial contaminations when axenic cultures need to be established. The life history of U. pinnatifida consists of the alternation between heteromorphic macroscopic sporophytes and microscopic gametophytes. The stark morphological and physiological differences between these two phases suggest that the composition of epiphytic microbial communities between them is likely different. However, studies on the composition of epiphytic microbial communities, especially comparison studies between sporophytes and gametophytes in U. pinnatifida are limited. The advent of high-throughput sequencing provides robust and efficient tools for studying the composition and relative abundance of the microbial community associated with the algae. In the present study, sporophytes and gametophytes (each with three biological replicates) of U. pinnatifida derived from the cultivated population in Dalian China were selected as the study objects. After DNA extraction and PCR amplification of the v3–v4 region of 16S rRNA gene and the v4 region of 18S rRNA gene, Illumina HiSeq 2500 high-throughput sequencing platform was used to sequence these specific regions. We identified and classified the composition of epiphytic microbial communities of the gametophytes and sporophytes of U. pinnatifida based on the sequencing results. A total of 446 932 effective reads were obtained through 16S rRNA gene sequencing. The raw reads have been submitted to the GenBank database (https://www.ncbi.nlm.nih.gov/) with the accession number PRJNA823903. The bacterial community composition of gametophyte and sporophyte was revealed to be significantly different, and the diversity of the bacterial community in gametophyte samples was higher than that in sporophyte samples. In gametophytes, Proteobacteria (66.67%) was the most dominant phylum, followed by Bacteroidetes (13.48%) and Cyanobacteria (11.13%). At the class level, Alphaproteobacteria (34.58%) was the most abundant, followed by Gammaproteobacteria (31.01%), Bacteroidia (13.16%), and Oxyphotobacteria (11.13%). Cyanobacteria (95.67%) was predominantly detected in sporophytes, followed by Actinobacteria (1.65%) and Firmicutes (1.48%). The distribution of Oxyphotobacteria, Alphaproteobacteria, Bacteroidia, Gammaproteobacteria, Negativicutes, OM190, Acidimicrobiia, Erysipelotrichia, Planctomycetacia, and Verrucomicrobiae were found to be different between gametophyte and sporophyte samples, among which OM190, Acidimicrobiia and Planctomycetacia were unique to gametophytes. The genus-level bacterial groups detected in gametophyte samples were Lewinella (10.06%), Leucothrix (5.99%), Sulfitobacter (4.06%), Bifidobacterium (0.02%), while Bifidobacterium accounted for 1.41% of the bacterial genus of sporophyte samples. There were 57.37% and 95.68% uncultured bacterium in gametophytes and sporophytes, respectively. We obtained a total of 473 770 effective reads through 18S rRNA gene sequencing. A major share (97.22%) of microeukaryotes in gametophytes were unclassified, while in sporophytes, the number was 94.95%. Streptophyta, Intramacronucleata, Basidiomycota, Apicomplexa, Arthropoda, Bacillariophyta, Chordata, Gastrotricha, Ascomycota, and Mucoromycota were detected both in the gametophytes and sporophytes. Among them, Basidiomycota, Ascomycota, and Mucoromycota belong to fungi. The community abundance of sporophyte samples was higher than that of gametophytes. In gametophyte samples, except for Phaeophyceae (88.77%) to which U. pinnatifida belongs, Copepoda of Arthropoda, Mediophyceae of Bacillariophyta, Mammalia of Chordata, Prostomatea of Intramacronucleata, and Liliopsida were dominant, with a proportion of 0.62%, 0.50%, 0.25%, 0.23%, and 0.23%, respectively. In addition to Phaeophyceae (94.49%), Conoidasida of Protozoa, Agaricomycetes of Basidiomycota, Spirotrichea of Intramacronucleata and Mammalia of Chordata were predominant in sporophytes, accounting for 0.91%, 0.83%, 0.51% and 0.24% of OTUs, respectively. Chytridiomycetes, Nassophorea, Colpodea, Tremellomycetes, Sordariomycetes, Conoidasida, Agaricomycetes, Arachnida, and Chromadorea were only detected in the sporophytes, and there was a significant difference in Spirotrichea abundance between gametophytes and sporophytes. In conclusion, the composition of epiphytic microbial communities and the relative abundance of different bacteria and microeukaryotes in the sporophytes and gametophytes of U. pinnatifida were determined through high-throughput sequencing of the amplicons of the v3–v4 region of 16S rRNA gene and the v4 region of 18S rRNA gene. Remarkable differences were revealed between the two life stages, indicating that their growth and development are associated with different microbial communities. The results of this study provide valuable information for sustainable cultivation and stock culture conservation of this important kelp species

Revealing the Hemispherical Shielding Effect of SiO2@Ag Composite Nanospheres to Improve the Surface Enhanced Raman Scattering Performance

Many studies widely used SiO2@Ag composite nanospheres for surface enhanced Raman scattering (SERS), which mainly contributes to electromagnetic enhancement. In addition to experiments, previous simulations mostly adopted a two-dimensional model in SERS research, resulting in the three-dimensional information being folded and masked. In this paper, we adopted the three-dimensional model to simulate the electric field distribution of SiO2@Ag composite nanospheres. It is found that when the Ag nanoparticles are distributed densely on the surface of SiO2 nanospheres, light cannot pass through the upper hemisphere due to the local surface plasmon resonance (LSPR) of the Ag nanoparticles, resulting in the upper hemisphere shielding effect; and if there are no Ag nanoparticles distributed densely on the surface of SiO2 nanospheres, the strong LSPR cannot be formed, so the incident light will be guided downward through the whispering gallery mode of the spherical structure. At the same time, we designed relevant experiments to synthesize SiO2@Ag composite nanosphere as SERS substrate and used Rhodamine 6G as a probe molecule to study its SERS performance. This design achieved a significant SERS effect, and is very consistent with our simulation results

Additional file 1: of Construction of a high-density genetic map and mapping of a sex-linked locus for the brown alga Undaria pinnatifida (Phaeophyceae) based on large scale marker development by specific length amplified fragment (SLAF) sequencing

Sequences of the mapped SLAF markers and genotype of the mapping samples. (PDF 9946 kb

Genetic Analysis of a recently established Undaria Pinnatifida (Laminariales: Alariaceae) population in the northern Wadden Sea reveals close proximity between drifting Thalli and the attached population

© 2019, © 2019 British Phycological Society. Undaria pinnatifida, a kelp species native to East Asia, has become cosmopolitan and drawn increasing attention due to its worldwide spread in recent decades. Floating fragments of this alga were found washed ashore on Sylt in 2016, the first record of this species in Germany. Thalli attached to local oyster reefs were detected in 2017. The genetic relationship between the floating and attached thalli on Sylt, as well as their relevance to the populations from northern Europe and native regions, was hitherto unknown. Here, 10 microsatellite markers were used to assess relationships between the recently established population on Sylt and five other northern European populations in France (Brittany, West English Channel), the Netherlands and England (Plymouth, West English Channel) plus three natural populations in China. Almost no genetic differentiation was detected between the floating and attached populations on Sylt, but they were genetically distinct from all the other studied northern European populations. The very low genetic diversity revealed in the new founder populations of Sylt suggests that they came from genetically similar parents. The marked reduction in both the number of alleles and heterozygosity in the northern European populations, as compared with the Chinese ones, is typical of founder effects in recently populated regions. Prominent genetic divergence was found between most of the northern European populations except those within Brittany and Sylt. Further studies will focus on identifying the putative source populations that might be found on shellfish farms, in local marinas or the benthic habitats around Sylt Island