Dimethyl sulfide mediates microbial predator-prey interactions between zooplankton and algae in the ocean

Plastic Litter Emits the Foraging Infochemical Dimethyl Sulfide after Submersion in Freshwater Rivers

Plastic pollution is widespread throughout aquatic environments globally, with many organisms known to interact with and ingest plastic. In marine environments, microbial biofilms that form on plastic surfaces can produce the odorous compound dimethyl sulfide (DMS), which is a known foraging cue. This has been shown to increase the ingestion of plastic by some invertebrates and therefore act as a biological factor which influences the risks of plastic to marine ecosystems. In freshwater however, the production of DMS has been largely overlooked, despite the known sensitivity of some freshwater species to this compound. To address this gap, the present study analyzed the production of DMS by biofilms which formed on low-density polyethylene and polylactic acid films after 3 and 6 weeks of submersion in either a rural or an urban United Kingdom river. Using gas chromatography-mass spectrometry, the production of DMS by these biofilms was consistently identified. The amount of DMS produced varied significantly across river locations and materials, with surfaces in the urban river generally producing a stronger signal and plastics producing up to seven times more DMS than glass control surfaces. Analysis of biofilm weight and photosynthetic pigment content indicated differences in biofilm composition across conditions and suggested that DMS production was largely driven by nonphotosynthetic taxa. For the first time this work has documented the production of DMS by plastic litter after submersion in freshwater rivers. Further work is now needed to determine if, as seen in marine systems, this production of DMS can encourage the interaction of freshwater organisms with plastic litter and therefore operate as a biological risk factor in the impacts of plastic on freshwater environments. Environ Toxicol Chem 2024;43:1485-1496. © 2024 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

The micro-ecological feature of colonies is a potential strategy for Phaeocystis globosa bloom formation

Phaeocystis globosa is among the dominant microalgae associated with harmful algal blooms. P. globosa has a polymorphic life cycle and its ecological success has been attributed to algal colony formation, however, few studies have assessed differences in microbial communities and their functional profiles between intra- and extra-colonies during P. globosa blooms. To address this, environmental and metagenomics tools were used to conduct a time-series analysis of the bacterial composition and metabolic characteristics of intra- and extra-colonies during a natural P. globosa bloom. The results show that bacterial composition, biodiversity, and network interactions differed significantly between intra- and extra-colonies. Dominant extra-colonial bacteria were Bacteroidia and Saccharimonadis, while dominant intra-colonial bacteria included Alphaproteobacteria and Gammaproteobacteria. Despite the lower richness and diversity observed in the intra-colonial bacterial community, relative to extra-colonies, the complexity and interconnectedness of the intra-colonial networks were higher. Regarding bacterial function, more functional genes were enriched in substance metabolism (polysaccharides, iron element and dimethylsulfoniopropionate) and signal communication (quorum sensing, indoleacetic acid-IAA) pathways in intra- than in extra-colonies. Conceptual model construction showed that microbial cooperative synthesis of ammonium, vitamin B12, IAA, and siderophores were strongly related to the P. globosa bloom, particularly in the intra-colonial environment. Overall, our data highlight the differences in bacterial structure and functions within and outside the colony during P. globosa blooms. These findings represent fundamental information indicating that phenotypic heterogeneity is a selective strategy that improves microbial population competitiveness and environmental adaptation, benefiting P. globosa bloom formation and persistence.

A red algal polysaccharide influences the multicellular development of the choanoflagellate Salpingoeca rosetta

We uncovered an interaction between a choanoflagellate and alga, in which porphyran, a polysaccharide produced by the red alga Porphyra umbilicalis, induces multicellular development in the choanoflagellate Salpingoeca rosetta. We first noticed this possible interaction when we tested the growth of S. rosetta in media that was steeped with P. umbilicalis as a nutritional source. Under those conditions, S. rosetta formed multicellular rosette colonies even in the absence of any bacterial species that can induce rosette development. In biochemical purifications, we identified porphyran, a extracellular polysaccharide produced by red algae, as the rosette inducing factor The response of S. rosetta to porphyran provides a biochemical insight for associations between choanoflagellates and algae that have been observed since the earliest descriptions of choanoflagellates. Moreover, this work provides complementary evidence to ecological and geochemical studies that show the profound impact algae have exerted on eukaryotes and their evolution, including a rise in algal productivity that coincided with the origin of animals, the closest living relatives of choanoflagellates.

Influence of the community assemblage on sulfur distributions in the South China sea

Marine distribution of dimethylsulfoniopropionate (DMSP) and its cleavage product dimethyl sulfide (DMS) is greatly affected by the community structures of bacteria, phytoplankton, and zooplankton. Spatial distributions of dissolved and particulate DMSP (DMSPd,p), and DMS were measured and their relationships with DMSP lyase activity (DLA), abundance of DMSP-consuming bacteria (DCB), and the community structures of phytoplankton, zooplankton, and bacteria were determined during summer in the South China Sea (SCS). The depth distributions of DMSPd,p exhibited a similar trend with Chl a, reaching their maxima in the mixing layer. The DMS concentration was positively correlated with DCB abundance and DLA, indicating that DCB and DMSP lyase had a significant effect on DMS production. High DMS concentrations in the horizontal distribution coincided with high DCB abundance and DLA and may be due to the rapid growth of phytoplankton resulting from the high dissolved inorganic nitrogen concentration brought by the cold vortices. Moreover, the highest copepod abundance at station G3 coincided with the highest DMS concentrations there among stations B4, F2, and G3. These results suggest that copepod may play an important role in DMS production. The bacterial SAR11 clade was positively correlated with DLA, indicating its significant contribution to DMSP degradation in the SCS. These findings contribute to the understanding of the effect of the community assemblage on DMSP/DMS distributions in the SCS dominated by mesoscale vortices.

Facilitating Interskin Communication in Artificial Polymer Systems through Liquid Transfer

Chemical communication is a ubiquitous process in nature, and it has sparked interest in the development of electric-sense-based robotic perception systems with chemical components. Here, a novel liquid crystal polymer is introduced that combines the transferring, receiving, and sensing of chemical signals, providing a new principle to achieve chemical communication in robotic systems. This approach allows for the transfer of cargo between two polymer coatings, and the transfer can be monitored through an electrical signal. Additionally, cascade transfer can be achieved through this approach, as the transfer of cargo is not limited to only two coatings, but can continue from the second to a third coating. Furthermore, the two coatings can be infused with different reagents, and upon exchange, a reaction takes place to generate the desired species. The novel method of chemical communication that is developed presents a notable improvement in embodied perception. This advancement facilitates human-robot and robot-robot interactions and enhances the ability of robots to efficiently and accurately perform complex tasks in their environment.

Prostaglandin pathway activation in the diatom Skeletonema marinoi under grazer pressure

Prostaglandins (Pgs) are eicosanoid lipid mediators detected in all vertebrates, in some marine invertebrates, macroalgae and in diatoms, a class of eukaryotic microalgae composing the phytoplankton. The enzymes involved in the Pgs pathway were found to be differentially expressed in two strains of the diatom Skeletonema marinoi, named FE7 and FE60, already known to produce different levels of oxylipins, a class of secondary metabolites involved in the defence of diatoms against copepod predation, with FE7 being higher producer than FE60. In the present study we investigated the response of genes involved in the production of oxylipins and Pgs, evaluating their expression after the exposure to the copepod Temora stylifera. Our results highlighted a grazer feeding preference for FE60, the strain having low oxylipins content and reduced expression of Pgs enzymes, and an impact on the gene expression of the enzymes involved in oxylipins (i.e. lipoxygenase) and Pgs (i.e. cyclooxygenase) biosynthesis, especially in FE7. A time course evaluation of the gene expression over 24 h showed an upregulation of the essential enzyme in the Pgs pathway, the cyclooxygenase, in FE60 after 6 h of exposure to the grazer, differently from FE7 where no upregulation of gene expression in the presence of copepods was revealed. These results provide preliminary indications regarding the existence of a complex involvement of the Pgs pathway in the prey-predator interaction that requires further investigations.

Algal blooms in the ocean: hot spots for chemically mediated microbial interactions

The cycling of major nutrients in the ocean is affected by large-scale phytoplankton blooms, which are hot spots of microbial life. Diverse microbial interactions regulate bloom dynamics. At the single-cell level, interactions between microorganisms are mediated by small molecules in the chemical crosstalk that determines the type of interaction, ranging from mutualism to pathogenicity. Algae interact with viruses, bacteria, parasites, grazers and other algae to modulate algal cell fate, and these interactions are dependent on the environmental context. Recent advances in mass spectrometry and single-cell technologies have led to the discovery of a growing number of infochemicals - metabolites that convey information - revealing the ability of algal cells to govern biotic interactions in the ocean. The diversity of infochemicals seems to account for the specificity in cellular response during microbial communication. Given the immense impact of algal blooms on biogeochemical cycles and climate regulation, a major challenge is to elucidate how microscale interactions control the fate of carbon and the recycling of major elements in the ocean. In this Review, we discuss microbial interactions and the role of infochemicals in algal blooms. We further explore factors that can impact microbial interactions and the available tools to decipher them in the natural environment.

Herbicide leakage into seawater impacts primary productivity and zooplankton globally

Predicting the magnitude of herbicide impacts on marine primary productivity remains challenging because the extent of worldwide herbicide pollution in coastal waters and the concentration-response relationships of phytoplankton communities to multiple herbicides are unclear. By analyzing the spatiotemporal distribution of herbicides at 661 bay and gulf stations worldwide from 1990 to 2022, we determined median, third quartile and maximum concentrations of 12 triazine herbicides of 0.18 nmol L-1, 1.27 nmol L-1 and 29.50 nmol L-1 (95%Confidence Interval: CI 1.06, 1.47), respectively. Under current herbicide stress, phytoplankton primary productivity was inhibited by more than 5% at 25% of the sites and by more than 10% at 10% of the sites (95%CI 3.67, 4.34), due to the inhibition of highly abundant sensitive species, community structure/particle size succession (from Bacillariophyta to Dinophyceae and from nano-phytoplankton to micro-phytoplankton), and resulting growth rate reduction. Concurrently, due to food chain cascade effects, the dominant micro-zooplankton population shifted from larger copepod larvae to smaller unicellular ciliates, which might prolong the transmission process in marine food chain and reduce the primary productivity transmission efficiency. As herbicide application rates on farmlands worldwide are correlated with residues in their adjacent seas, a continued future increase in herbicide input may seriously affect the stability of coastal waters.

Aerobic methane production by phytoplankton as an important methane source of aquatic ecosystems: Reconsidering the global methane budget

Biological methane, a major source of global methane budget, is traditionally thought to be produced in anaerobic environments. However, the recent reports about methane supersaturation occurring in oxygenated water layer, termed as "methane paradox", have challenged this prevailing paradigm. Significantly, growing evidence has indicated that phytoplankton including prokaryotic cyanobacteria and eukaryotic algae are capable of generating methane under aerobic conditions. In this regard, a systematic review of aerobic methane production by phytoplankton is expected to arouse the public attention, contributing to the understanding of methane paradox. Here, we comprehensively summarize the widespread phenomena of methane supersaturation in oxic layers. The remarkable correlation relationships between methane concentration and several key indicators (depth, chlorophyll a level and organic sulfide concentration) indicate the significance of phytoplankton in in-situ methane accumulation. Subsequently, four mechanisms of aerobic methane production by phytoplankton are illustrated in detail, including photosynthesis-driven metabolism, reactive oxygen species (ROS)-driven demethylation of methyl donors, methanogenesis catalyzed by nitrogenase and demethylation of phosphonates catalyzed by CP lyase. The first two pathways occur in various phytoplankton, while the latter two have been specially discovered in cyanobacteria. Additionally, the effects of four crucial factors on aerobic methane production by phytoplankton are also discussed, including phytoplankton species, light, temperature and crucial nutrients. Finally, the measures to control global methane emissions from phytoplankton, the precise intracellular mechanisms of methane production and a more complete global methane budget model are definitely required in the future research on methane production by phytoplankton. This review would provide guidance for future studies of aerobic methane production by phytoplankton and emphasize the potential contribution of aquatic ecosystems to global methane budget.

Progress and challenges in exploring aquatic microbial communities using non-targeted metabolomics

Advances in bioanalytical technologies are constantly expanding our insights into complex ecosystems. Here, we highlight strategies and applications that make use of non-targeted metabolomics methods in aquatic chemical ecology research and discuss opportunities and remaining challenges of mass spectrometry-based methods to broaden our understanding of environmental systems.

Identification and Photochemistry of the Mercaptomethyl Radical

The mercaptomethyl radical (·CH2SH) is a higher-energy isomer of the methylthio radical (CH3S·) that has been proposed as an important intermediate in atmospheric and interstellar sulfur chemistry. Herein, we report the spectroscopic identification of ·CH2SH during the UV (365 nm) photolysis of CH3S· in a solid Ar-matrix at 10 K. Upon subsequent irradiation at 266 nm, the dehydrogenation of ·CH2SH to yield CS via the intermediacy of the elusive thioformyl radical (HCS·) has also been observed. The characterization of ·CH2SH and HCS· with matrix-isolation IR and UV-vis spectroscopy is supported by 13C-isotope labeling and quantum chemical calculations at the CCSD(T)-F12a/cc-pVTZ-F12 level using configuration-selective vibrational configuration interaction theory (VCI). The disclosed photochemistry of ·CH2SH provides new insight into understanding the chemical evolution of organosulfur molecules in the interstellar medium (ISM).

SAR92 clade bacteria are potentially important DMSP degraders and sources of climate-active gases in marine environments

Dimethylsulfoniopropionate (DMSP) is one of Earth's most abundant organosulfur molecules, which can be catabolized by marine bacteria to release climate-active gases through the cleavage and/or demethylation pathways. The marine SAR92 clade is an abundant oligotrophic group of Gammaproteobacteria in coastal seawater, but their ability to catabolize DMSP is untested. Three SAR92 clade strains isolated from coastal seawater in this study and the SAR92 representative strain HTCC2207 were all shown to catabolize DMSP as a carbon source. All the SAR92 clade strains exhibited DMSP lyase activity producing dimethylsulfide (DMS) and their genomes encoded a ratified DddD DMSP lyase. In contrast, only HTCC2207 and two isolated strains contained the DMSP demethylase dmdA gene and potentially simultaneously demethylated and cleaved DMSP to produce methanethiol (MeSH) and DMS. In SAR92 clade strains with dddD and dmdA, transcription of these genes was inducible by DMSP substrate. Bioinformatic analysis indicated that SAR92 clade bacteria containing and transcribing DddD and DmdA were widely distributed in global oceans, especially in polar regions. This study highlights the SAR92 clade of oligotrophic bacteria as potentially important catabolizers of DMSP and sources of the climate-active gases MeSH and DMS in marine environments, particularly in polar regions.IMPORTANCECatabolism of dimethylsulfoniopropionate (DMSP) by marine bacteria has important impacts on the global sulfur cycle and climate. However, whether and how members of most oligotrophic bacterial groups participate in DMSP metabolism in marine environments remains largely unknown. In this study, by characterizing culturable strains, we have revealed that bacteria of the SAR92 clade, an abundant oligotrophic group of Gammaproteobacteria in coastal seawater, can catabolize DMSP through the DMSP lyase DddD-mediated cleavage pathway and/or the DMSP demethylase DmdA-mediated demethylation pathway to produce climate-active gases dimethylsulfide and methanethiol. Additionally, we found that SAR92 clade bacteria capable of catabolizing DMSP are widely distributed in global oceans. These results indicate that SAR92 clade bacteria are potentially important DMSP degraders and sources of climate-active gases in marine environments that have been overlooked, contributing to a better understanding of the roles and mechanisms of the oligotrophic bacteria in oceanic DMSP degradation.

The role of microbe-microplastic associations in marine Nematode feeding behaviors

Fauna across many taxa and trophic levels have been shown to consume microplastics (MPs) in experiments, providing evidence that supports field-based gut content assessments. Multiple explanations exist regarding why fauna consume MPs, one of which posits that microbial growth on MPs may facilitate faunal ingestion. However, laboratory assessments on the reasons why MPs are consumed remain limited. Here, we assessed if the presence of microbes on MPs altered marine nematode feeding behaviors across current and potential future concentrations of MPs in a local system. We used a microcosm experiment in which field-collected sediment was spiked with bacterially treated or untreated fluorescent plastic microbeads (1.0-5.0 μm) in concentrations of 102, 104, and 106 per microcosm, representing local and potential future concentrations of MPs. Ingestion by the dominant interstitial fauna was investigated after 0, 3, and 7 days using bright field microscopy. Nematodes were the only fauna across microcosms that consumed MPs, but this consumption was variable and there were no apparent trends across exposure time, bacterial treatment, or MP concentration. There were also no genera- or feeding-type-specific trends in the number of MPs consumed, though four of the top five nematode genera that consumed MPs were pollution-tolerant genera. Our study demonstrates that microbe-MP associations do not drive marine nematodes to eat MPs, especially at local field concentrations. While there were no trends across any of the nematode genera in our study, we recognize that unrealistic MP concentrations in other studies may provide alternative explanations for nematode consumption of MPs.

Dimethylsulfoniopropionate and its catabolites are important chemical signals mediating marine microbial interactions

Dimethylsulfoniopropionate (DMSP) is a ubiquitous organosulfur compound with key ecological roles in marine environments. This paper offers a brief insight into the mechanisms, environmental diversity, and importance of DMSP-mediated marine microbial interactions, including algae-microzooplankton interactions, bacteria-microzooplankton interactions, and algae-bacteria interactions. We also highlight current challenges that warrant further investigation.

Phylogeny and biogeography of the algal DMS-releasing enzyme in the global ocean

Phytoplankton produce the volatile dimethyl sulfide (DMS), an important infochemical mediating microbial interactions, which is also emitted to the atmosphere and affecting the global climate. Albeit the enzymatic source for DMS in eukaryotes was elucidated, namely a DMSP lyase (DL) called Alma1, we still lack basic knowledge regarding its taxonomic distribution. We defined unique sequence motifs which enable the identification of DL homologs (DLHs) in model systems and environmental populations. We used these motifs to predict DLHs in diverse algae by analyzing hundreds of genomic and transcriptomic sequences from model systems under stress conditions and from environmental samples. Our findings show that the DL enzyme is more taxonomically widespread than previously thought, as it is encoded by known algal taxa as haptophytes and dinoflagellates, but also by chlorophytes, pelagophytes and diatoms, which were conventionally considered to lack the DL enzyme. By exploring the Tara Oceans database, we showed that DLHs are widespread across the oceans and are predominantly expressed by dinoflagellates. Certain dinoflagellate DLHs were differentially expressed between the euphotic and mesopelagic zones, suggesting a functional specialization and an involvement in the metabolic plasticity of mixotrophic dinoflagellates. In specific regions as the Southern Ocean, DLH expression by haptophytes and diatoms was correlated with environmental drivers such as nutrient availability. The expanded repertoire of putative DL enzymes from diverse microbial origins and geographic niches suggests new potential players in the marine sulfur cycle and provides a foundation to study the cellular function of the DL enzyme in marine microbes.

Molecular discoveries in microbial DMSP synthesis

Dimethylsulfoniopropionate (DMSP) is one of the Earth's most abundant organosulfur compounds because many marine algae, bacteria, corals and some plants produce it to high mM intracellular concentrations. In these organisms, DMSP acts an anti-stress molecule with purported roles to protect against salinity, temperature, oxidative stress and hydrostatic pressure, amongst many other reported functions. However, DMSP is best known for being a major precursor of the climate-active gases and signalling molecules dimethylsulfide (DMS), methanethiol (MeSH) and, potentially, methane, through microbial DMSP catabolism. DMSP catabolism has been extensively studied and the microbes, pathways and enzymes involved have largely been elucidated through the application of molecular research over the last 17 years. In contrast, the molecular biology of DMSP synthesis is a much newer field, with the first DMSP synthesis enzymes only being identified in the last 5 years. In this review, we discuss how the elucidation of key DMSP synthesis enzymes has greatly expanded our knowledge of the diversity of DMSP-producing organisms, the pathways used, and what environmental factors regulate production, as well as to inform on the physiological roles of DMSP. Importantly, the identification of key DMSP synthesis enzymes in the major groups of DMSP producers has allowed scientists to study the distribution and predict the importance of different DMSP-producing organisms to global DMSP production in diverse marine and sediment environments. Finally, we highlight key challenges for future molecular research into DMSP synthesis that need addressing to better understand the cycling of this important marine organosulfur compound, and its magnitude in the environment.

Aerobic methylation of hydrogen sulfide to dimethylsulfide in diverse microorganisms and environments

Dimethylsulfide (DMS) is the major biosulfur source emitted to the atmosphere with key roles in global sulfur cycling and potentially climate regulation. The main precursor of DMS is thought to be dimethylsulfoniopropionate. However, hydrogen sulfide (H₂S), a widely distributed and abundant volatile in natural environments, can be methylated to DMS. The microorganisms and the enzymes that convert H₂S to DMS, and their importance in global sulfur cycling were unknown. Here we demonstrate that the bacterial MddA enzyme, previously known as a methanethiol S-methyltransferase, could methylate inorganic H₂S to DMS. We determine key residues involved in MddA catalysis and propose the mechanism for H₂S S-methylation. These results enabled subsequent identification of functional MddA enzymes in abundant haloarchaea and a diverse range of algae, thus expanding the significance of MddA mediated H₂S methylation to other domains of life. Furthermore, we provide evidence for H₂S S-methylation being a detoxification strategy in microorganisms. The mddA gene was abundant in diverse environments including marine sediments, lake sediments, hydrothermal vents and soils. Thus, the significance of MddA-driven methylation of inorganic H₂S to global DMS production and sulfur cycling has likely been considerably underestimated.

Airborne dimethyl sulfide (DMS) cues dimethylsulfoniopropionate (DMSP) increases in the intertidal green alga Ulva fenestrata

Although the use of airborne molecules as infochemicals is common in terrestrial plants, it has not been shown to occur in an ecologically relevant context in marine seaweeds. Like terrestrial plants, intertidal plants spend part of their lives emersed at low tide and release volatile organic compounds (VOCs) into the air when they are grazed or physiologically stressed. We hypothesized seaweeds could use airborne VOCs as infochemicals and respond to them by upregulating a keystone defensive metabolite, dimethylsulfoniopropionate (DMSP). We conducted laboratory and field experiments in which Ulva fenestrata was exposed to airborne dimethyl sulfide (DMS), a volatile antiherbivore and antioxidant metabolite released when the seaweed is grazed or physiologically stressed. In the laboratory, U. fenestrata exposed to DMS had 43-48% higher DMSP concentrations, relative to controls, 6-9 days after exposure. In the field, U. fenestrata 1 m downwind of DMS emitters had 19% higher DMSP concentrations than upwind seaweeds after 11 days. To our knowledge, this is the first demonstration of a marine plant using an airborne molecule released when damaged to elicit defensive responses. Our study suggests that the ability to detect airborne compounds has evolved multiple times or before the divergence of terrestrial plants and green algae.

A new dimethylsulfoniopropionate lyase of the cupin superfamily in marine bacteria

Dimethylsulfoniopropionate (DMSP) is a marine organosulfur compound with important roles in stress protection, marine biogeochemical cycling, chemical signalling and atmospheric chemistry. Diverse marine microorganisms catabolize DMSP via DMSP lyases to generate the climate-cooling gas and info-chemical dimethyl sulphide. Abundant marine heterotrophs of the Roseobacter group (MRG) are well known for their ability to catabolize DMSP via diverse DMSP lyases. Here, a new DMSP lyase DddU within the MRG strain Amylibacter cionae H-12 and other related bacteria was identified. DddU is a cupin superfamily DMSP lyase like DddL, DddQ, DddW, DddK and DddY, but shares <15% amino acid sequence identity with these enzymes. Moreover, DddU proteins forms a distinct clade from these other cupin-containing DMSP lyases. Structural prediction and mutational analyses suggested that a conserved tyrosine residue is the key catalytic amino acid residue in DddU. Bioinformatic analysis indicated that the dddU gene, mainly from Alphaproteobacteria, is widely distributed in the Atlantic, Pacific, Indian and polar oceans. For reference, dddU is less abundant than dddP, dddQ and dddK, but much more frequent than dddW, dddY and dddL in marine environments. This study broadens our knowledge on the diversity of DMSP lyases, and enhances our understanding of marine DMSP biotransformation.

Bacterial lifestyle switch in response to algal metabolites

Unicellular algae, termed phytoplankton, greatly impact the marine environment by serving as the basis of marine food webs and by playing central roles in the biogeochemical cycling of elements. The interactions between phytoplankton and heterotrophic bacteria affect the fitness of both partners. It is becoming increasingly recognized that metabolic exchange determines the nature of such interactions, but the underlying molecular mechanisms remain underexplored. Here, we investigated the molecular and metabolic basis for the bacterial lifestyle switch, from coexistence to pathogenicity, in Sulfitobacter D7 during its interaction with Emiliania huxleyi, a cosmopolitan bloom-forming phytoplankter. To unravel the bacterial lifestyle switch, we analyzed bacterial transcriptomes in response to exudates derived from algae in exponential growth and stationary phase, which supported the Sulfitobacter D7 coexistence and pathogenicity lifestyles, respectively. In pathogenic mode, Sulfitobacter D7 upregulated flagellar motility and diverse transport systems, presumably to maximize assimilation of E. huxleyi-derived metabolites released by algal cells upon cell death. Algal dimethylsulfoniopropionate (DMSP) was a pivotal signaling molecule that mediated the transition between the lifestyles, supporting our previous findings. However, the coexisting and pathogenic lifestyles were evident only in the presence of additional algal metabolites. Specifically, we discovered that algae-produced benzoate promoted the growth of Sulfitobacter D7 and hindered the DMSP-induced lifestyle switch to pathogenicity, demonstrating that benzoate is important for maintaining the coexistence of algae and bacteria. We propose that bacteria can sense the physiological state of the algal host through changes in the metabolic composition, which will determine the bacterial lifestyle during interaction.

The Co-Evolution Aspects of the Biogeochemical Role of Phytoplankton in Aquatic Ecosystems: A Review

In freshwater and marine ecosystems, the phytoplankton community is based on microalgae and cyanobacteria, which include phylogenetically very diverse groups of oxygenic photoautotrophs. In the process of evolution, they developed a wide range of bio(geo)chemical adaptations that allow them to effectively use solar radiation, CO₂, and nutrients, as well as major and trace elements, to form O₂ and organic compounds with a high chemical bond energy. The inclusion of chemical elements in the key processes of energy and plastic metabolism in the cell is determined by redox conditions and the abundance and metabolic availability of elements in the paleoenvironment. Geochemical evolution, which proceeded simultaneously with the evolution of biosystems, contributed to an increase in the number of metals and trace elements acting as cofactors of enzymes involved in metabolism and maintaining homeostasis in the first photoautotrophs. The diversity of metal-containing enzymes and the adaptive ability to replace one element with another without losing the functional properties of enzymes ensured the high ecological plasticity of species and allowed microalgae and cyanobacteria to successfully colonize a wide variety of habitats. In this review, we consider the main aspects of the modern concepts of the biogeochemical evolution of aquatic ecosystems and the role of some metals in the main bioenergetic processes in photosynthetic prokaryotes and eukaryotes. We present generalized data on the efficiency of the assimilation of key nutrients by phytoplankton and their importance in the cycle of carbon, silicon, nitrogen, phosphorus, sulfur, and iron. This article presents modern views on the evolutionary prerequisites for the formation of elemental signatures in different systematic groups of microalgae, as well as the possibility of using the stoichiometric ratio in the study of biological and geochemical processes in aquatic ecosystems.

Functional modulation of chemical mediators in microbial communities

Interactions between microorganisms are often mediated by specialized metabolites. Although the structures and biosynthesis of these compounds may have been elucidated, microbes exist within complex microbiomes and chemical signals can thus also be subject to community-dependent modifications. Increasingly powerful chemical and biological tools allow to shed light on this poorly understood aspect of chemical ecology. We provide an overview of loss-of-function and gain-of-function chemical mediator (CM) modifications within microbial multipartner relationships. Although loss-of-function modifications are abundant in the literature, few gain-of-function modifications have been described despite their important role in microbial interactions. Research in this field holds great potential for our understanding of microbial interactions and may also provide novel tools for targeted interference with microbial signaling.

Microbial community composition and metabolic potential during a succession of algal blooms from Skeletonema sp. to Phaeocystis sp

Elucidating the interactions between algal and microbial communities is essential for understanding the dynamic mechanisms regulating algal blooms in the marine environment. Shifts in bacterial communities when a single species dominates algal blooms have been extensively investigated. However, bacterioplankton community dynamics during bloom succession when one algal species shift to another is still poorly understood. In this study, we used metagenomic analysis to investigate the bacterial community composition and function during algal bloom succession from Skeletonema sp. to Phaeocystis sp. The results revealed that bacterial community structure and function shifted with bloom succession. The dominant group in the Skeletonema bloom was Alphaproteobacteria, while Bacteroidia and Gammaproteobacteria dominated the Phaeocystis bloom. The most noticeable feature during the successions was the change from Rhodobacteraceae to Flavobacteriaceae in the bacterial communities. The Shannon diversity indices were significantly higher in the transitional phase of the two blooms. Metabolic reconstruction of the metagenome-assembled genomes (MAGs) showed that dominant bacteria exhibited some environmental adaptability in both blooms, capable of metabolizing the main organic compounds, and possibly providing inorganic sulfur to the host algae. Moreover, we identified specific metabolic capabilities of cofactor biosynthesis (e.g., B vitamins) in MAGs in the two algal blooms. In the Skeletonema bloom, Rhodobacteraceae family members might participate in synthesizing vitamin B₁ and B₁₂ to the host, whereas in the Phaeocystis bloom, Flavobacteriaceae was the potential contributor for synthesizing vitamin B₇ to the host. In addition, signal communication (quorum sensing and indole-3-acetic acid molecules) might have also participated in the bacterial response to bloom succession. Bloom-associated microorganisms showed a noticeable response in composition and function to algal succession. The changes in bacterial community structure and function might be an internal driving factor for the bloom succession.

Spatio-Temporal Variations of Zooplankton and Correlations with Environmental Parameters around Tiaowei Island, Fujian, China

The present study illustrates zooplankton dynamics in relation to environmental factors from the surrounding area of Tiaowei Island based on ten seasonal sampling cruises over three years. A total of 116 species of zooplankton were collected with a predominance of Copepoda (mainly consisting of Centropagidae, Oithonidae, Acartia, Labidocera and Paracalanus), accounting for 31.6 % of the total number of species. The diversity indices indicated a relatively high richness, abundance and evenness of zooplankton ranging from 2.794 to 4.012 on the Shannon-Wiener index for each cruise. More than 20 species of Cnidaria medusae are found as gelatinous organisms, which not only compete with fish but also potentially cause disasters. Significant seasonal variations were detected in both the zooplankton structure and environmental variables. NMDS illustrated a highly overlapping community structure in spring, autumn and winter, while the zooplankton composition in the summer was different from that of the other three seasons with a higher diversity index. Meanwhile, out of thirteen environmental parameters, eight varied significantly among seasons but there were no significant variations among stations. The biota-environmental relationship following a redundancy analysis revealed that water temperature, pH, salinity, dissolved oxygen and suspended particulate composition were the main environmental parameters, seasonally impacting the zooplankton communities. Planktonic larvae (such as nauplius larvae and branchyura zoea) and some zooplankton (including Corophium sinensis and Oithonasimilis) were significantly vulnerable to the dynamics of suspended particulate composition and water temperature.

Programmed cell death process in freshwater Microcystis aeruginosa and marine Phaeocystis globosa induced by a plant derived allelochemical

Harmful algal blooms (HAB) are a serious problem worldwide. Allelochemicals from natural plants were recently thought to be promising anti-algaecide in controlling harmful algae. However, the programmed cell death (PCD) process of algae under allelopathic pressure induced by 5,4'-dihydroxyflavone (5,4'-DHF) was poorly understood. In this study, two common and worldwide distributed microalgae, Microcystis aeruginosa and Phaeocystis globosa were selected as target algae, and the PCD processes induced by 5,4'-DHF were cross-compared between the two species. Both algae species were inhibited significantly by 5,4'-DHF with the relative sensitivity of 0.11. To uncover the PCD progress systematically, signals for PCD triggering, antioxidant enzyme activity, photosynthetic ability variation, caspase-like activities and typical indicators were investigated. In both species, typical indicators of PCD - phosphatidylserine externalization and chromatin condensation - were detected. The intracellular reactive oxygen species (ROS), nitric oxide (NO) and H₂O₂ were the potential signal molecules to stimulate PCD, and caspase-like activities were activated with an elevation of cytochrome c indicating the initiation of PCD in both species. However, P. globosa responded to 5,4'-DHF immediately after 3 h with the elevation of ROS and not in M. aeruginosa. Antioxidant enzyme activities of superoxide dismutase (SOD) and catalase (CAT) in M. aeruginosa and P. globosa also showed different patterns on day 3. Specifically, SOD activity in M. aeruginosa increased significantly while it decreased significantly in P. globosa, CAT activity in M. aeruginosa decreased significantly while it increased significantly in P. globosa (p < 0.05). Malondialdehyde (MDA) content in P. globosa increased significantly (p < 0.001) while it showed no variation in M. aeruginosa. Overall, this study is one of the earliest studies to explore the inhibition and action mechanism of plant derived flavonoids on harmful algae from the perspective of PCD, and provide new insights into the antialgal mechanism of allelochemicals.

Droplets in underlying chemical communication recreate cell interaction behaviors

The sensory-motor interaction is a hallmark of living systems. However, developing inanimate systems with “recognize and attack” abilities remains challenging. On the other hand, controlling the inter-droplet dynamics on surfaces is key in microengineering and biomedical applications. We show here that a pair of droplets can become intelligently interactive (chemospecific stimulus-response inter-droplet autonomous operation) when placed on a nanoporous thin film surface. We find an attacker-victim-like non-reciprocal interaction between spatially separated droplets leading to an only-in-one shape instability that triggers a drop projection to selectively couple, resembling cellular phenomenologies such as pseudopod emission and phagocytic-like functions. The nanopore-driven underlying communication and associated chemical activity are the main physical ingredients behind the observed behavior. Our results reveal that basic features found in many living cell types can emerge from a simple two-droplet framework. This work is a promising step towards the design of microfluidic smart robotics and for origin-of-life protocell models.

While a hallmark of living systems, developing sensory-motor interactions in inanimate systems remains challenging. Here, authors show that nanoporous surfaces can be used to create stimuli-responsive droplet interplay with shape transformation and complex behaviours reminiscent of living cell actions.