Bacterial lipopolysaccharide induces settlement and metamorphosis in a marine larva

Marine Delivery Vehicles: Molecular Components and Applications of Bacterial Extracellular Vesicles

In marine ecosystems, communication among microorganisms is crucial since the distance is significant if considered on a microbial scale. One of the ways to reduce this gap is through the production of extracellular vesicles, which can transport molecules to guarantee nutrients to the cells. Marine bacteria release extracellular vesicles (EVs), small membrane-bound structures of 40 nm to 1 µm diameter, into their surrounding environment. The vesicles contain various cellular compounds, including lipids, proteins, nucleic acids, and glycans. EVs may contribute to dissolved organic carbon, thus facilitating heterotroph growth. This review will focus on marine bacterial EVs, analyzing their structure, composition, functions, and applications.

Outer membrane vesicles from commensal microbes contribute to the sponge Tedania sp. development by regulating the expression level of apoptosis-inducing factor (AIF)

The transition from the swimming larval stage to the settlement stage represents a significant node in the marine sponge developmental process. Previous research has shown that the outer membrane vesicles (OMVs) from the bacterial species Tenacibaculum mesophilum associated with the sponge Tedania sp. influence larval settlement: low concentrations of OMVs increase the attachment rate, whereas high concentrations decrease the attachment rate. Here, by comparing the transcriptomes of sponge larvae in filtered seawater (FSW group) and in FSW supplemented with OMVs (FSW-OMV group), the results indicated that bacterial OMVs affected larval settlement by modulating the expression levels of apoptosis-inducing factor (AIF) in the host. Subsequently, quantitative real-time PCR revealed a decrease in aif expression near the time of settlement (SE) compared to that in the control group. RNA interference (RNAi) was used to target the aif gene, and the rate of larval settlement was significantly reduced, confirming the inhibitory effect of high concentrations of OMVs. Moreover, small RNA (sRNA) sequencing of OMVs revealed the existence of abundant AIF-sRNAs of 30 nt, further suggesting that one pathway for the involvement of sponge-associated bacteria in host development is the transport of OMVs and the direct function of cargo loading.

Bacterial envelope polysaccharide cues settlement and metamorphosis in the biofouling tubeworm Hydroides elegans

Metamorphosis for many marine invertebrates is triggered by external cues, commonly produced by bacteria. For larvae of Hydroides elegans, lipopolysaccharide (LPS) from the biofilm-dwelling bacterium Cellulophaga lytica induces metamorphosis. To determine whether bacterial LPS is a common metamorphosis-inducing factor for this species, we compare larval responses to LPS from 3 additional inductive Gram-negative marine biofilm bacteria with commercially available LPS from 3 bacteria not known to induce metamorphosis. LPS from all the inductive bacteria trigger metamorphosis, while LPS from non-inductive isolated marine bacteria do not. We then ask, which part of the LPS is the inductive element, the lipid (Lipid-A) or the polysaccharide (O-antigen), and find it is the latter for all four inductive bacteria. Finally, we examine the LPS subunits from two strains of the same bacterial species, one inductive and the other not, and find the LPS and O-antigen to be inductive from only the inductive bacterial strain.

Inter-kingdom communication and the sympoietic way of life

Organisms are now seen as holobionts, consortia of several species that interact metabolically such that they sustain and scaffold each other's existence and propagation. Sympoiesis, the development of the symbiotic relationships that form holobionts, is critical for our understanding the origins and maintenance of biodiversity. Rather than being the read-out of a single genome, development has been found to be sympoietic, based on multigenomic interactions between zygote-derived cells and symbiotic microbes. These symbiotic and sympoietic interactions are predicated on the ability of cells from different kingdoms of life (e.g., bacteria and animals) to communicate with one another and to have their chemical signals interpreted in a manner that facilitates development. Sympoiesis, the creation of an entity by the interactions of other entities, is commonly seen in embryogenesis (e.g., the creation of lenses and retinas through the interaction of brain and epidermal compartments). In holobiont sympoiesis, interactions between partners of different domains of life interact to form organs and biofilms, wherein each of these domains acts as the environment for the other. If evolution is forged by changes in development, and if symbionts are routinely involved in our development, then changes in sympoiesis can constitute an important factor in evolution.

Bacterial c-di-GMP triggers metamorphosis of mussel larvae through a STING receptor

Bacteria induced metamorphosis observed in nearly all marine invertebrates. However, the mechanism of bacteria regulating the larvae-juvenile metamorphosis remains unknown. Here, we test the hypothesis that c-di-GMP, a ubiquitous bacterial second-messenger molecule, directly triggers the mollusc Mytilus coruscus larval metamorphosis via the stimulator of interferon genes (STING) receptor. We determined that the deletion of c-di-GMP synthesis genes resulted in reduced c-di-GMP levels and biofilm-inducing activity on larval metamorphosis, accompanied by alterations in extracellular polymeric substances. Additionally, c-di-GMP extracted from tested varying marine bacteria all exhibited inducing activity on larval metamorphosis. Simultaneously, through pharmacological and molecular experiments, we demonstrated that M. coruscus STING (McSTING) participates in larval metamorphosis by binding with c-di-GMP. Our findings reveal that new role of bacterial c-di-GMP that triggers mussel larval metamorphosis transition, and extend knowledge in the interaction of bacteria and host development in marine ecosystems.

Bacterial c-di-GMP signaling gene affects mussel larval metamorphosis through outer membrane vesicles and lipopolysaccharides

Biofilms serve as crucial cues for settlement and metamorphosis in marine invertebrates. Within bacterial systems, c-di-GMP functions as a pivotal signaling molecule regulating both biofilm formation and dispersion. However, the molecular mechanism of how c-di-GMP modulates biofilm-induced larval metamorphosis remains elusive. Our study reveals that the deletion of a c-di-GMP related gene in Pseudoalteromonas marina led to an increase in the level of bacterial c-di-GMP by knockout technique, and the mutant strain had an enhanced ability to produce more outer membrane vesicles (OMVs) and lipopolysaccharides (LPS). The mutant biofilms had higher induction activity for larval metamorphosis in mussels Mytilus coruscus, and OMVs play a major role in the induction activity. We further explored the function of LPS in OMVs. Extracted LPS induced high larval metamorphosis rate, and LPS content were subject to c-di-GMP and LPS-biosynthesis gene. Thus, we postulate that the impact of c-di-GMP on biofilm-induced metamorphosis is mediated through OMVs and LPS.

Ecological benefits of artificial light at night (ALAN): Accelerating the development and metamorphosis of marine shellfish larvae

Urbanization has led to increasing use of artificial light at night (ALAN), which has rapidly become an important source of pollution in many cities. To identify the ALAN effects on the embryonic development of the Pacific abalone Haliotis discus hannai, we first exposed larvae to natural light with a light period of 12 L:12D (control, Group CTR). We then exposed larvae to three different light regimes. Larvae in Group NL were exposed to full spectrum artificial light from 18:00 to 00:00 to simulate the lighting condition at night, whereas Groups BL and YL were illuminated at the same time interval with 450 nm of short-wavelength blue light and 560 nm of long-wavelength orange light, respectively, to simulate billboard lighting at night. There were significantly higher hatching success and metamorphosis rates of larvae in Group BL than in Group YL or CTR (P < 0.05). The larvae in Group YL had the highest abnormality rate and took the longest time to complete metamorphosis. Transcriptomic studies revealed significantly higher expression levels of genes related to RNA transport, DNA replication, and protein processing in endoplasmic reticulum pathways in Group BL compared to the other groups. In the metabolomic analysis, we identified prostaglandin B1, tyramine, d-fructose 6-phosphate, L-adrenaline, leukotriene C4, and arachidonic acid as differential metabolic markers, as they play a vital part in helping larvae adapt to different ALAN conditions. Multi-omics correlation analysis of pairwise comparisons between all of the groups suggested that the biosynthesis of unsaturated fatty acids (FAs) and arachidonic acid metabolism pathways were significantly enriched (P < 0.05). Further quantitative analysis of the fatty acid (FA) contents revealed that 42 out of 50 FAs were down-regulated in Group BL and up-regulated in Group YL, which suggested that the synthesis, catabolism, and metabolism of FAs are crucial for the larval response to different spectral components of ALAN. For the first time, we report positive rather than negative effects of artificial blue light at night on the embryonic development of a benthic marine species. These results are significant for unbiased and full-scale assessment of the ecological effects of ALAN and for understanding the structural stability of the marine benthic community.

Crude Oil and Its Burnt Residues Induce Metamorphosis in Marine Invertebrates

Metamorphosis is a critical process in the life cycle of most marine benthic invertebrates, determining their transition from plankton to benthos. It affects dispersal and settlement and therefore decisively influences the dynamics of marine invertebrate populations. An extended period of metamorphic competence is an adaptive feature of numerous invertebrate species that increases the likelihood of finding a habitat suitable for settlement and survival. We found that crude oil and residues of burnt oil rapidly induce metamorphosis in two different marine invertebrate larvae, a previously unknown sublethal effect of oil pollution. When exposed to environmentally realistic oil concentrations, up to 84% of tested echinoderm larvae responded by undergoing metamorphosis. Similarly, up to 87% of gastropod larvae metamorphosed in response to burnt oil residues. This study demonstrates that crude oil and its burned residues can act as metamorphic inducers in marine planktonic larvae, short-circuiting adaptive metamorphic delay. Future studies on molecular pathways and oil-bacteria-metamorphosis interactions are needed to fully understand the direct or indirect mechanisms of oil-induced metamorphosis in marine invertebrates. With 90% of chronic oiling occurring in coastal areas, this previously undescribed impact of crude oil on planktonic larvae may have global implications for marine invertebrate populations and biodiversity.

Future research directions of the model marine tubeworm Hydroides elegans and synthesis of developmental staging of the complete life cycle

BACKGROUND

The biofouling marine tube worm, Hydroides elegans, is an indirect developing polychaete with significance as a model organism for questions in developmental biology and the evolution of host-microbe interactions. However, a complete description of the life cycle from fertilization through sexual maturity remains scattered in the literature, and lacks standardization.

RESULTS AND DISCUSSION

Here, we present a unified staging scheme synthesizing the major morphological changes that occur during the entire life cycle of the animal. These data represent a complete record of the life cycle, and serve as a foundation for connecting molecular changes with morphology.

CONCLUSIONS

The present synthesis and associated staging scheme are especially timely as this system gains traction within research communities. Characterizing the Hydroides life cycle is essential for investigating the molecular mechanisms that drive major developmental transitions, like metamorphosis, in response to bacteria.

Coral larval settlement induction using tissue-associated and exuded coralline algae metabolites and the identification of putative chemical cues

Reef-building crustose coralline algae (CCA) are known to facilitate the settlement and metamorphosis of scleractinian coral larvae. In recent decades, CCA coverage has fallen globally and degrading environmental conditions continue to reduce coral survivorship, spurring new restoration interventions to rebuild coral reef health. In this study, naturally produced chemical compounds (metabolites) were collected from two pantropical CCA genera to isolate and classify those that induce coral settlement. In experiments using four ecologically important Caribbean coral species, we demonstrate the applicability of extracted, CCA-derived metabolites to improve larval settlement success in coral breeding and restoration efforts. Tissue-associated CCA metabolites induced settlement of one coral species, Orbicella faveolata, while metabolites exuded by CCA (exometabolites) induced settlement of three species: Acropora palmata, Colpophyllia natans and Orbicella faveolata. In a follow-up experiment, CCA exometabolites fractionated and preserved using two different extraction resins induced the same level of larval settlement as the unfractionated positive control exometabolites. The fractionated CCA exometabolite pools were characterized using liquid chromatography tandem mass spectrometry, yielding 145 distinct molecular subnetworks that were statistically defined as CCA-derived and could be classified into 10 broad chemical classes. Identifying these compounds can reveal their natural prevalence in coral reef habitats and facilitate the development of new applications to enhance larval settlement and the survival of coral juveniles.

Induction of larval settlement in crown-of-thorns starfish is not mediated by conspecific cues

Population irruptions of crown-of-thorns starfish (COTS; Acanthaster spp.) remain a major cause of coral reef degradation throughout the Pacific and Indian Oceans and are inherently modulated by larval settlement and recruitment success. Gregarious larval settlement, as exhibited by many other ecologically important marine invertebrates, can catalyse population growth and replenishment. However, whether conspecific cues induce or influence the settlement of COTS larvae remains a critical information gap. This experimental study examined the induction of COTS settlement in response to a range of conspecific cues associated with early- and late-stage herbivorous juveniles, corallivorous juveniles and adults. Competent COTS larvae were generally not induced to settle by the presence of conspecifics or cues associated with conspecifics, while the settlement success of COTS in the presence of coralline algae was not inhibited or enhanced by adding conspecific conditioned seawater. Rather than being reinforced by gregarious settlement, the recruitment of COTS populations appears dependent on associative settlement cues (i.e., coralline algae and/or associated microbial communities) signalling suitable benthic habitat.

Chemically mediated rheotaxis of endangered tri-spine horseshoe crab: potential dispersing mechanism to vegetated nursery habitats along the coast

Background

An enhanced understanding of larval ecology is fundamental to improve the management of locally depleted horseshoe crab populations in Asia. Recent studies in the northern Beibu Gulf, China demonstrated that nesting sites of Asian horseshoe crabs are typically close to their nursery beaches with high-density juveniles distributed around mangrove, seagrass and other structured habitats.

Methods

A laboratory Y-maze chamber was used to test whether the dispersal of early-stage juvenile tri-spine horseshoe crab Tachypleus tridentatus is facilitated by chemical cues to approach suitable nursery habitats. The juvenile orientation to either side of the chamber containing controlled seawater or another with various vegetation cues, as well as their movement time, the largest distance and displacement were recorded.

Results

The juveniles preferred to orient toward seagrass Halophila beccarii cues when the concentration reached 0.5 g l^-1, but ceased at 2 g l^-1. The results can be interpreted as a shelter-seeking process to get closer to the preferred settlement habitats. However, the juveniles exhibited avoidance behaviors in the presence of mangrove Avicennia marina and invasive saltmarsh cordgrass Spartina alterniflora at 2 g l^-1. The juveniles also spent less time moving in the presence of the A. marina cue, as well as reduced displacement in water containing the S. alterniflora cue at 1 and 2 g l^-1. These results may explain the absence of juvenile T. tridentatus within densely vegetated areas, which have generally higher organic matter and hydrogen sulfide.

Conclusion

Early-stage juvenile T. tridentatus are capable of detecting and responding to habitat chemical cues, which can help guide them to high-quality settlement habitats. Preserving and restoring seagrass beds in the intertidal areas should be prioritized when formulating habitat conservation and management initiatives for the declining horseshoe crab populations.

Bacterial biofilm colonization and succession in tropical marine waters are similar across different types of stone materials used in seawall construction

Seawalls are important in protecting coastlines from currents, erosion, sea-level rise, and flooding. They are, however, associated with reduced biodiversity, due to their steep orientation, lack of microhabitats, and the materials used in their construction. Hence, there is considerable interest in modifying seawalls to enhance the settlement and diversity of marine organisms, as microbial biofilms play a critical role facilitating algal and invertebrate colonization. We assessed how different stone materials, ranging from aluminosilicates to limestone and concrete, affect biofilm formation. Metagenomic assessment of marine microbial communities indicated no significant impact of material on microbial diversity, irrespective of the diverse surface chemistry and topography. Based on KEGG pathway analysis, surface properties appeared to influence the community composition and function during the initial stages of biofilm development, but this effect disappeared by Day 31. We conclude that marine biofilms converged over time to a generic marine biofilm, rather than the underlying stone substrata type playing a significant role in driving community composition.

Signalling molecules inducing metamorphosis in marine organisms

Covering: findings from early 1980s until early 2022Microbial-derived cues of marine biofilms induce settlement and metamorphosis of marine organisms, a process responsible for the emergence of diverse flora and fauna in marine habitats. Although this phenomenon is known for more than 80 years, the research field has only recently gained much momentum. Here, we summarize the currently existing biochemical and microbial knowledge about microbial signalling molecules, con-specific signals, and synthetic compounds that induce or prevent recruitment, settlement, and metamorphosis in invertebrate larvae. We discuss the possible modes of action and conclude with perspectives for future research directions in the field of marine chemical ecology.

Symbiosis of disciplines: how can developmental biologists join conservationists in sustaining and restoring earth's biodiversity?

What can developmental biology contribute toward mitigating the consequences of anthropogenic assaults on the environment and climate change? In this Spotlight article, we advocate a developmental biology that takes seriously Lynn Margulis' claim that 'the environment is part of the body'. We believe this to be a pre-condition for developmental biology playing important roles in conservation and environmental restoration. We need to forge a developmental biology of the holobiont - the multi-genomic physiologically integrated organism that is also a functional biome. To this end, we highlight how developmental biology needs to explore more deeply the interactions between developing organisms, and their chemical, physical and biotic environments.