Identification of proteins in the adhesive trails of the diatom Amphora coffeaeformis

Development of a new kappa-carrageenan hydrogel system to study benthic diatom vertical movements

Benthic diatom vertical movement has been investigated mainly through indirect measurements based on chlorophyll a fluorescence and spectral reflectance signals. The presence of sediment hinders direct imaging and grazers activity renders the work under controlled conditions very difficult. This study provides a tool to study diatoms movement in a 3D hydrogel matrix. Synthetic and natural hydrogels were tested to find the best 3D transparent scaffold where diatoms could grow and freely move in all directions. Polyamidoamines (PAAm) hydrogels were no-cytocompatible and hyaluronic acid (HA) only allowed diatoms to survive for 2-days. Natural hydrogels made of gelatin/Na-alginate, Na-alginate and kappa-carrageenan (KC) were cytocompatible, with KC showing the best properties for diatom growth and movement on a long term (up to 2 months). Comparing Nitzschia spathulata, Gyrosigma limosum and Navicula phyllepta growth in liquid media vs in KC gels, we found that diatoms reached a significantly higher final biomass in the hydrogel condition. Hydrogels were also useful to isolate large size diatom species e.g., Nitzschia elongata, that did not survive in suspension. Finally, we showed three ways to study diatom species-specific movement in KC hydrogels: 1) controlled species mix; 2) natural diatom assemblages with grazers; and 3) natural diatom assemblages without grazers. With our system, single diatoms could be imaged, identified, and counted. In addition, different stimuli, e.g., light intensity and light composition can be applied and their effects on movement and physiology studied without being masked by sediment or impaired by meiofauna.

Declines in ice cover are accompanied by light limitation responses and community change in freshwater diatoms

The rediscovery of diatom blooms embedded within and beneath the Lake Erie ice cover (2007-2012) ignited interest in psychrophilic adaptations and winter limnology. Subsequent studies determined the vital role ice plays in winter diatom ecophysiology as diatoms partition to the underside of ice, thereby fixing their location within the photic zone. Yet, climate change has led to widespread ice decline across the Great Lakes, with Lake Erie presenting a nearly "ice-free" state in several recent winters. It has been hypothesized that the resultant turbid, isothermal water column induces light limitation amongst winter diatoms and thus serves as a competitive disadvantage. To investigate this hypothesis, we conducted a physiochemical and metatranscriptomic survey that spanned spatial, temporal, and climatic gradients of the winter Lake Erie water column (2019-2020). Our results suggest that ice-free conditions decreased planktonic diatom bloom magnitude and altered diatom community composition. Diatoms increased their expression of various photosynthetic genes and iron transporters, which suggests that the diatoms are attempting to increase their quantity of photosystems and light-harvesting components (a well-defined indicator of light limitation). We identified two gene families which serve to increase diatom fitness in the turbid ice-free water column: proton-pumping rhodopsins (a potential second means of light-driven energy acquisition) and fasciclins (a means to "raft" together to increase buoyancy and co-locate to the surface to optimize light acquisition). With large-scale climatic changes already underway, our observations provide insight into how diatoms respond to the dynamic ice conditions of today and shed light on how they will fare in a climatically altered tomorrow.

Diatom adhesive trail proteins acquired by horizontal gene transfer from bacteria serve as primers for marine biofilm formation

Biofilm-forming benthic diatoms are key primary producers in coastal habitats, where they frequently dominate sunlit intertidal substrata. The development of gliding motility in raphid diatoms was a key molecular adaptation that contributed to their evolutionary success. However, the structure-function correlation between diatom adhesives utilized for gliding and their relationship to the extracellular matrix that constitutes the diatom biofilm is unknown. Here, we have used proteomics, immunolocalization, comparative genomics, phylogenetics and structural homology analysis to investigate the evolutionary history and function of diatom adhesive proteins. Our study identified eight proteins from the adhesive trails of Craspedostauros australis, of which four form a new protein family called Trailins that contain an enigmatic Choice-of-Anchor A (CAA) domain, which was acquired through horizontal gene transfer from bacteria. Notably, the CAA-domain shares a striking structural similarity with one of the most widespread domains found in ice-binding proteins (IPR021884). Our work offers new insights into the molecular basis for diatom biofilm formation, shedding light on the function and evolution of diatom adhesive proteins. This discovery suggests that there is a transition in the composition of biomolecules required for initial surface colonization and those utilized for 3D biofilm matrix formation.

Cooperative motility, force generation and mechanosensing in a foraging non-photosynthetic diatom

Diatoms are ancestrally photosynthetic microalgae. However, some underwent a major evolutionary transition, losing photosynthesis to become obligate heterotrophs. The molecular and physiological basis for this transition is unclear. Here, we isolate and characterize new strains of non-photosynthetic diatoms from the coastal waters of Singapore. These diatoms occupy diverse ecological niches and display glucose-mediated catabolite repression, a classical feature of bacterial and fungal heterotrophs. Live-cell imaging reveals deposition of secreted extracellular polymeric substance (EPS). Diatoms moving on pre-existing EPS trails (runners) move faster than those laying new trails (blazers). This leads to cell-to-cell coupling where runners can push blazers to make them move faster. Calibrated micropipettes measure substantial single-cell pushing forces, which are consistent with high-order myosin motor cooperativity. Collisions that impede forward motion induce reversal, revealing navigation-related force sensing. Together, these data identify aspects of metabolism and motility that are likely to promote and underpin diatom heterotrophy.

Biodegradation efficacy of selected marine microalgae against Low-Density Polyethylene (LDPE): An environment friendly green approach

The present study dealt with the five marine microalgae strains viz., Chloroidium saccharophilum, Picochlorum maculatum, Amphora sp., Hymenomonas globosa and Limnospira indica and their effective degradation ability of Low-Density Polyethylene for the period of 45 days. The incubation of LDPE in microalgae culture has resulted in the maximum weight loss (20.16 ± 0.14 %), higher reduction rate (0.005/day) and lower half-life (138.4 days) in the LDPE treated with P. maculatum. The SEM images of all treated LDPE revealed surface erosion and the ATR-FTIR spectra showed functional group peaks along with new peaks at 1369.35 cm^-1, 2332.96 cm^-1 and 500-726 cm^-1. Carbonyl (Keto, Ester), Vinyl and Internal double bond indices increased significantly in all the treated groups. The crystallinity was decreased (64.13 %) in P. maculatum treated LDPE than the control (71.37 %). Thermogravimetric analysis showed the reduction in thermal stability after biodegradation. This efficient microalgal degradation as a bioremediation technique will reduce the plastic pollution.

Marine biofouling and the role of biocidal coatings in balancing environmental impacts

Marine biofouling is a global problem affecting various industries, particularly the shipping industry due to long-distance voyages across various ecosystems. Therein fouled hulls cause increased fuel consumption, greenhouse gas emissions, and the spread of invasive aquatic species. To counteract these issues, biofouling management plans are employed using manual cleaning protocols and protective coatings. This review provides a comprehensive overview of adhesion strategies of marine organisms, and currently available mitigation methods. Further, recent developments and open challenges of antifouling (AF) and fouling release (FR) coatings are discussed with regards to the future regulatory environment. Finally, an overview of the environmental and economic impact of fouling is provided to point out why and when the use of biocidal solutions is beneficial in the overall perspective.

On the role of cell surface associated, mucin-like glycoproteins in the pennate diatom Craspedostauros australis (Bacillariophyceae)

Diatoms are single-celled microalgae with silica-based cell walls (frustules) that are abundantly present in aquatic habitats, and form the basis of the food chain in many ecosystems. Many benthic diatoms have the remarkable ability to glide on all natural or man-made underwater surfaces using a carbohydrate- and protein-based adhesive to generate traction. Previously, three glycoproteins, termed FACs (Frustule Associated Components), have been identified from the common fouling diatom Craspedostauros australis and were implicated in surface adhesion through inhibition studies with a glycan-specific antibody. The polypeptide sequences of FACs remained unknown, and it was unresolved whether the FAC glycoproteins are indeed involved in adhesion, or whether this is achieved by different components sharing the same glycan epitope with FACs. Here we have determined the polypeptide sequences of FACs using peptide mapping by LC-MS/MS. Unexpectedly, FACs share the same polypeptide backbone (termed CaFAP1), which has a domain structure of alternating Cys-rich and Pro-Thr/Ser-rich regions reminiscent of the gel-forming mucins. By developing a genetic transformation system for C. australis, we were able to directly investigate the function of CaFAP1-based glycoproteins in vivo. GFP-tagging of CaFAP1 revealed that it constitutes a coat around all parts of the frustule and is not an integral component of the adhesive. CaFAP1-GFP producing transformants exhibited the same properties as wild type cells regarding surface adhesion and motility speed. Our results demonstrate that FAC glycoproteins are not involved in adhesion and motility, but might rather act as a lubricant to prevent fouling of the diatom surface.

Genome evolution of a nonparasitic secondary heterotroph, the diatom Nitzschia putrida

Secondary loss of photosynthesis is observed across almost all plastid-bearing branches of the eukaryotic tree of life. However, genome-based insights into the transition from a phototroph into a secondary heterotroph have so far only been revealed for parasitic species. Free-living organisms can yield unique insights into the evolutionary consequence of the loss of photosynthesis, as the parasitic lifestyle requires specific adaptations to host environments. Here, we report on the diploid genome of the free-living diatom Nitzschia putrida (35 Mbp), a nonphotosynthetic osmotroph whose photosynthetic relatives contribute ca. 40% of net oceanic primary production. Comparative analyses with photosynthetic diatoms and heterotrophic algae with parasitic lifestyle revealed that a combination of gene loss, the accumulation of genes involved in organic carbon degradation, a unique secretome, and the rapid divergence of conserved gene families involved in cell wall and extracellular metabolism appear to have facilitated the lifestyle of a free-living secondary heterotroph.

Amphiphilic Nitroxide-Bearing Siloxane-Based Block Copolymer Coatings for Enhanced Marine Fouling Release

The buildup of organic matter and organisms on surfaces exposed to marine environments, known as biofouling, is a disruptive and costly process affecting maritime operations. Previous research has identified some of the surface characteristics particularly suited to the creation of antifouling and fouling-release surfaces, but there remains room for improvement against both macrofouling and microfouling organisms. Characterization of their adhesives has shown that many rely on oxidative chemistries. In this work, we explore the incorporation of the stable radical 2,2,6,6-tetramethylpipiderin-1-oxyl (TEMPO) as a component in an amphiphilic block copolymer system to act as an inhibitor for marine cements, disrupting adhesion of macrofouling organisms. Using polystyrene-b-poly(dimethylsiloxane-r-vinylmethysiloxane) block copolymers, pendent vinyl groups were functionalized with TEMPO and poly(ethylene glycol) to construct an amphiphilic material with redox active character. The antifouling and fouling-release performance of these materials was investigated through settlement and removal assays of three model fouling organisms and correlated to surface structure and chemistry. Surfaces showed significant antifouling character and fouling-release performance was increased substantially toward barnacles by the incorporation of stable radicals, indicating their potential for marine antifouling applications.

Cytoskeletal diversification across 1 billion years: What red algae can teach us about the cytoskeleton, and vice versa

The cytoskeleton has a central role in eukaryotic biology, enabling cells to organize internally, polarize, and translocate. Studying cytoskeletal machinery across the tree of life can identify common elements, illuminate fundamental mechanisms, and provide insight into processes specific to less-characterized organisms. Red algae represent an ancient lineage that is diverse, ecologically significant, and biomedically relevant. Recent genomic analysis shows that red algae have a surprising paucity of cytoskeletal elements, particularly molecular motors. Here, we review the genomic and cell biological evidence and propose testable models of how red algal cells might perform processes including cell motility, cytokinesis, intracellular transport, and secretion, given their reduced cytoskeletons. In addition to enhancing understanding of red algae and lineages that evolved from red algal endosymbioses (e.g., apicomplexan parasites), these ideas may also provide insight into cytoskeletal processes in animal cells.

Mating type specific transcriptomic response to sex inducing pheromone in the pennate diatom Seminavis robusta

Sexual reproduction is a fundamental phase in the life cycle of most diatoms. Despite its role as a source of genetic variation, it is rarely reported in natural circumstances and its molecular foundations remain largely unknown. Here, we integrate independent transcriptomic datasets to prioritize genes responding to sex inducing pheromones (SIPs) in the pennate diatom Seminavis robusta. We observe marked gene expression changes associated with SIP treatment in both mating types, including an inhibition of S phase progression, chloroplast division, mitosis, and cell wall formation. Meanwhile, meiotic genes are upregulated in response to SIP, including a sexually induced diatom specific cyclin. Our data further suggest an important role for reactive oxygen species, energy metabolism, and cGMP signaling during the early stages of sexual reproduction. In addition, we identify several genes with a mating type specific response to SIP, and link their expression pattern with physiological specialization, such as the production of the attraction pheromone diproline in mating type - (MT-) and mate-searching behavior in mating type + (MT+). Combined, our results provide a model for early sexual reproduction in pennate diatoms and significantly expand the suite of target genes to detect sexual reproduction events in natural diatom populations.

Recent Developments in Biomimetic Antifouling Materials: A Review

The term 'biomimetic' might be applied to any material or process that in some way reproduces, mimics, or is otherwise inspired by nature. Also variously termed bionic, bioinspired, biological design, or even green design, the idea of adapting or taking inspiration from a natural solution to solve a modern engineering problem has been of scientific interest since it was first proposed in the 1960s. Since then, the concept that natural materials and nature can provide inspiration for incredible breakthroughs and developments in terms of new technologies and entirely new approaches to solving technological problems has become widely accepted. This is very much evident in the fields of materials science, surface science, and coatings. In this review, we survey recent developments (primarily those within the last decade) in biomimetic approaches to antifouling, self-cleaning, or anti-biofilm technologies. We find that this field continues to mature, and emerging novel, biomimetic technologies are present at multiple stages in the development pipeline, with some becoming commercially available. However, we also note that the rate of commercialization of these technologies appears slow compared to the significant research output within the field.

The Seminavis robusta genome provides insights into the evolutionary adaptations of benthic diatoms

Benthic diatoms are the main primary producers in shallow freshwater and coastal environments, fulfilling important ecological functions such as nutrient cycling and sediment stabilization. However, little is known about their evolutionary adaptations to these highly structured but heterogeneous environments. Here, we report a reference genome for the marine biofilm-forming diatom Seminavis robusta, showing that gene family expansions are responsible for a quarter of all 36,254 protein-coding genes. Tandem duplications play a key role in extending the repertoire of specific gene functions, including light and oxygen sensing, which are probably central for its adaptation to benthic habitats. Genes differentially expressed during interactions with bacteria are strongly conserved in other benthic diatoms while many species-specific genes are strongly upregulated during sexual reproduction. Combined with re-sequencing data from 48 strains, our results offer insights into the genetic diversity and gene functions in benthic diatoms.

Molecular insights into the powerful mucus-based adhesion of limpets (Patella vulgata L.)

Limpets (Patella vulgata L.) are renowned for their powerful attachments to rocks on wave-swept seashores. Unlike adult barnacles and mussels, limpets do not adhere permanently; instead, they repeatedly transition between long-term adhesion and locomotive adhesion depending on the tide. Recent studies on the adhesive secretions (bio-adhesives) of marine invertebrates have expanded our knowledge on the composition and function of temporary and permanent bio-adhesives. In comparison, our understanding of the limpets' transitory adhesion remains limited. In this study, we demonstrate that suction is not the primary attachment mechanism in P. vulgata; rather, they secrete specialized pedal mucus for glue-like adhesion. Through combined transcriptomics and proteomics, we identified 171 protein sequences from the pedal mucus. Several of these proteins contain conserved domains found in temporary bio-adhesives from sea stars, sea urchins, marine flatworms and sea anemones. Many of these proteins share homology with fibrous gel-forming glycoproteins, including fibrillin, hemolectin and SCO-spondin. Moreover, proteins with potential protein- and glycan-degrading domains could have an immune defence role or assist degrading adhesive mucus to facilitate the transition from stationary to locomotive states. We also discovered glycosylation patterns unique to the pedal mucus, indicating that specific sugars may be involved in transitory adhesion. Our findings elucidate the mechanisms underlying P. vulgata adhesion and provide opportunities for future studies on bio-adhesives that form strong attachments and resist degradation until necessary for locomotion.