Corals, like other cnidarians, are venomous animals that rely on stinging cells (nematocytes) and their toxins to catch prey and defend themselves against predators. However, little is known about ...the chemical arsenal employed by stony corals, despite their ecological importance. Here, we show large differences in the density of nematocysts and whole-body hemolytic activity between different species of reef-building corals. In the branched coral Stylophora pistillata, the tips of the branches exhibited a greater hemolytic activity than the bases. Hemolytic activity and nematocyst density were significantly lower in Stylophora that were maintained for close to a year in captivity compared to corals collected from the wild. A cysteine-containing actinoporin was identified in Stylophora following partial purification and tandem mass spectrometry. This toxin, named Δ-Pocilopotoxin-Spi1 (Δ-PCTX-Spi1) is the first hemolytic toxin to be partially isolated and characterized in true reef-building corals. Loss of hemolytic activity during chromatography suggests that this actinoporin is only one of potentially several hemolytic molecules. These results suggest that the capacity to employ offensive and defensive chemicals by corals is a dynamic trait within and between coral species, and provide a first step towards identifying the molecular components of the coral chemical armament.
Coral reefs are among the most diverse, complex and densely populated marine ecosystems. To survive, morphologically simple and sessile cnidarians have developed mechanisms to catch prey, deter ...predators and compete with adjacent corals for space, yet the mechanisms underlying these functions are largely unknown. Here, we characterize the histology, toxic activity and gene expression patterns in two different types of tentacles from the scleractinian coral Galaxea fascilcularis - catch tentacles (CTs), used to catch prey and deter predators, and sweeper tentacles (STs), specialized tentacles used for territorial aggression.
STs exhibit more mucocytes and higher expression of mucin genes than CTs, and lack the ectodermal cilia used to deliver food to the mouth and remove debris. STs and CTs also express different sensory rhodopsin-like g-protein coupled receptors, suggesting they may employ different sensory pathways. Each tentacle type has a different complement of stinging cells (nematocytes), and the expression in the two tentacles of genes encoding structural nematocyte proteins suggests the stinging cells develop within the tentacles. CTs have higher neurotoxicity to blowfly larvae and hemolytic activity compared to the STs, consistent with a role in prey capture. In contrast, STs have higher phospholipase A2 activity, which we speculate may have a role in inducing tissue damage during territorial aggression. The expression of genes encoding cytolytic toxins (actinoporins) and phospholipases also differs between the tentacle types.
These results show that the same organism utilizes two distinct tentacle types, each equipped with a different venom apparatus and toxin composition, for prey capture and defense and for territorial aggression.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Ecosystem dynamics in monomictic lakes are characterized by seasonal thermal mixing and stratification. These physical processes bring about seasonal variations in nutrients and organic matter ...fluxes, affecting the biogeochemical processes that occur in the water column. Physical and chemical dynamics are generally reflected in seasonal structural changes in the phytoplankton and bacterio-plankton community. In this study, we analyzed, using 16S rRNA amplicon sequencing, the structure of the bacterial community associated with large particles (>20 μm) in Lake Kinneret (Sea of Galilee, Israel), and its associations to phytoplankton populations. The study was carried out during late winter and early spring, a highly dynamic period in terms of thermal mixing, nutrient availability, and shifts in phytoplankton composition. Structural changes in the bacterioplankton population corresponded with limnological variations in the lake. In terms of the entire heterotrophic community, the structural patterns of particle-associated bacteria were mainly correlated with abiotic factors such as pH, ammonia, water temperature and nitrate. However, analysis of microbial taxon-specific correlations with phytoplankton species revealed a strong potential link between specific bacterial populations and the presence of different phytoplankton species, such as the cyanobacterium Microcystis, as well as the dinoflagellates Peridinium and Peridiniopsis. We found that Brevundimonas, a common freshwater genus, and Bdellovibrio, a well-known Gram-negative bacteria predator, were positively associated to Microcystis, suggesting a potentially important role of these three taxa in the microbial ecology of the lake. Our results show that the dynamics of environmental abiotic conditions, rather than specific phytoplankton assemblages, are the main factors positively correlated with changes in the community structure as a whole. Nevertheless, some specific bacteria may interact and be linked with specific phytoplankton, which may potentially control the dynamic patterns of the microbial community.
Our understanding of secondary metabolite production in bacteria has been shaped primarily by studies of attached varieties such as symbionts, pathogens, and soil bacteria. Here we show that a strain ...of the single-celled, planktonic marine cyanobacterium PROCHLOROCOCCUS:which conducts a sizable fraction of photosynthesis in the oceans--produces many cyclic, lanthionine-containing peptides (lantipeptides). Remarkably, in Prochlorococcus MIT9313 a single promiscuous enzyme transforms up to 29 different linear ribosomally synthesized peptides into a library of polycyclic, conformationally constrained products with highly diverse ring topologies. Genes encoding this system are found in variable abundances across the oceans--with a hot spot in a Galapagos hypersaline lagoon--suggesting they play a habitat- and/or community-specific role. The extraordinarily efficient pathway for generating structural diversity enables these cyanobacteria to produce as many secondary metabolites as model antibiotic-producing bacteria, but with much smaller genomes.
Microbial life in the oceans impacts the entire marine ecosystem, global biogeochemistry and climate. The marine cyanobacterium
, an abundant component of this ecosystem, releases a significant ...fraction of the carbon fixed through photosynthesis, but the amount, timing and molecular composition of released carbon are still poorly understood. These depend on several factors, including nutrient availability, light intensity and glycogen storage. Here we combine multiple computational approaches to provide insight into carbon storage and exudation in
. First, with the aid of a new algorithm for recursive filling of metabolic gaps (ReFill), and through substantial manual curation, we extended an existing genome-scale metabolic model of
MED4. In this revised model (
SO595), we decoupled glycogen biosynthesis/degradation from growth, thus enabling dynamic allocation of carbon storage. In contrast to standard implementations of flux balance modeling, we made use of forced influx of carbon and light into the cell, to recapitulate overflow metabolism due to the decoupling of photosynthesis and carbon fixation from growth during nutrient limitation. By using random sampling in the ensuing flux space, we found that storage of glycogen or exudation of organic acids are favored when the growth is nitrogen limited, while exudation of amino acids becomes more likely when phosphate is the limiting resource. We next used COMETS to simulate day-night cycles and found that the model displays dynamic glycogen allocation and exudation of organic acids. The switch from photosynthesis and glycogen storage to glycogen depletion is associated with a redistribution of fluxes from the Entner-Doudoroff to the Pentose Phosphate pathway. Finally, we show that specific gene knockouts in
SO595 exhibit dynamic anomalies compatible with experimental observations, further demonstrating the value of this model as a tool to probe the metabolic dynamic of
.
Corals make use of different chemical compounds during interactions with prey, predators and aggressors. Hydrogen Peroxide (H2O2) is produced and released by a wide range of organisms as part of ...their defense against grazers or pathogens. In coral reefs, the large fluxes and relatively long half-life of H2O2, make it a potentially important info-chemical or defense molecule. Here we describe a previously unstudied phenomenon of rapid H2O2 release from the reef-building coral Stylophora pistillata during feeding on zooplankton and in response to chemical and physical stimuli. Following stimuli, both symbiotic and bleached corals were found to rapidly release H2O2 to the surrounding water for a short period of time (few minutes). The H2O2 release was restricted to the site of stimulus, and an increase in physical stress and chemical stimuli concentration resulted in elevated H2O2 release. Omission of calcium (a key regulator of exocytotic processes) from the experimental medium inhibited H2O2 release. Hence we suggest that H2O2 is actively released in response to stimuli, rather than leaking passively from the coral tissue. We estimate that at the site of stimulus H2O2 can reach concentrations potentially high enough to deter predators or motile, potentially pathogenic, bacteria.
Lakes and other freshwater bodies are intimately connected to the surrounding land, yet to what extent land-use affects the quality of freshwater and the microbial communities living in various ...freshwater environments is largely unknown. We address this question through an analysis of the land use surrounding 46 inter-connected lakes located within seven different drainage basins in northern Germany, and the microbiomes of these lakes during early summer. Lake microbiome structure was not correlated with the specific drainage basin or by basin size, and bacterial distribution did not seem to be limited by distance. Instead, land use within the drainage basin could predict, to some extent, NO
+ NO
concentrations in the water, which (together with temperature,
and total phosphorus) correlated to some extent with the water microbiome structure. Land use directly surrounding the water bodies, however, had little observable effects on water quality or the microbiome. Several microbial lineages, including Cyanobacteria and Verrucomicrobia, were differentially partitioned between the lakes. Significantly more data, including time-series measurements of land use and water chemical properties, are needed to fully understand the interaction between the environment and the organization of microbial communities.
Cnidarians rely on their nematocysts and the venom injected through these unique weaponry systems to catch prey and protect themselves from predators. The development and physiology of the ...nematocysts of Hydra magnipapillata, a classic model organism, have been intensively studied, yet the composition and biochemical activity of their venom components are mostly unknown. Here, we show that hydra actinoporin-like toxins (HALTs), which have previously been associated with Hydra nematocysts, belong to a multigene family comprising six genes, which have diverged from a single common ancestor. All six genes are expressed in a population of Hydra magnipapillata. When expressed recombinantly, HALT-1 (Δ-HYTX-Hma1a), an actinoporin-like protein found in the stenoteles (the main penetrating nematocysts used in prey capture), reveals hemolytic activity, albeit about two-thirds lower than that of the anemone actinoporin equinatoxin II (EqTII, Δ-AITX-Aeq1a). HALT-1 also differs from EqTII in the size of its pores, and likely does not utilize sphingomyelin as a membrane receptor. We describe features of the HALT-1 sequence which may contribute to this difference in activity, and speculate on the role of this unusual family of pore-forming toxins in the ecology of Hydra.
•The Hydra genome encodes six Hydra actinoporin-like toxin (HALT) genes, all of which are expressed in laboratory populations.•Hydra's HALTs are phylogenetically distinct from anemone actinoporins.•HALT genes differ from hemolytic and lethal anemone toxins in several important sequence features.•We expressed and purified HALT-1, a toxin previously found in the nematocysts used for prey capture (stenoteles).•HALT-1 reveals lower hemolytic activity, a larger pore size and different lipid affinity compared to Equinatoxin II.
Microbial communities, through their metabolism, drive carbon cycling in marine environments. These complex communities are composed of many different microorganisms including heterotrophic bacteria, ...each with its own nutritional needs and metabolic capabilities. Yet, models of ecosystem processes typically treat heterotrophic bacteria as a "black box," which does not resolve metabolic heterogeneity nor address ecologically important processes such as the successive modification of different types of organic matter. Here we directly address the heterogeneity of metabolism by characterizing the carbon source utilization preferences of 63 heterotrophic bacteria representative of several major marine clades. By systematically growing these bacteria on 10 media containing specific subsets of carbon sources found in marine biomass, we obtained a phenotypic fingerprint that we used to explore the relationship between metabolic preferences and phylogenetic or genomic features. At the class level, these bacteria display broadly conserved patterns of preference for different carbon sources. Despite these broad taxonomic trends, growth profiles correlate poorly with phylogenetic distance or genome-wide gene content. However, metabolic preferences are strongly predicted by a handful of key enzymes that preferentially belong to a few enriched metabolic pathways, such as those involved in glyoxylate metabolism and biofilm formation. We find that enriched pathways point to enzymes directly involved in the metabolism of the corresponding carbon source and suggest potential associations between metabolic preferences and other ecologically relevant traits. The availability of systematic phenotypes across multiple synthetic media constitutes a valuable resource for future quantitative modeling efforts and systematic studies of interspecies interactions.
Half of the Earth's annual primary production is carried out by phytoplankton in the surface ocean. However, this metabolic activity is heavily impacted by heterotrophic bacteria, which dominate the transformation of organic matter released from phytoplankton. Here, we characterize the diversity of metabolic preferences across many representative heterotrophs by systematically growing them on different fractions of dissolved organic carbon. Our analysis suggests that different clades of bacteria have substantially distinct preferences for specific carbon sources, in a way that cannot be simply mapped onto phylogeny. These preferences are associated with the presence of specific genes and pathways, reflecting an association between metabolic capabilities and ecological lifestyles. In addition to helping understand the importance of heterotrophs under different conditions, the phenotypic fingerprint we obtained can help build higher resolution quantitative models of global microbial activity and biogeochemical cycles in the oceans.
Prochlorococcus is the numerically dominant phototroph in the oligotrophic subtropical ocean and carries out a significant fraction of marine primary productivity. Although field studies have ...provided evidence for nitrate uptake by Prochlorococcus, little is known about this trait because axenic cultures capable of growth on nitrate have not been available. Additionally, all previously sequenced genomes lacked the genes necessary for nitrate assimilation. Here we introduce three Prochlorococcus strains capable of growth on nitrate and analyze their physiology and genome architecture. We show that the growth of high-light (HL) adapted strains on nitrate is ∼17% slower than their growth on ammonium. By analyzing 41 Prochlorococcus genomes, we find that genes for nitrate assimilation have been gained multiple times during the evolution of this group, and can be found in at least three lineages. In low-light adapted strains, nitrate assimilation genes are located in the same genomic context as in marine Synechococcus. These genes are located elsewhere in HL adapted strains and may often exist as a stable genetic acquisition as suggested by the striking degree of similarity in the order, phylogeny and location of these genes in one HL adapted strain and a consensus assembly of environmental Prochlorococcus metagenome sequences. In another HL adapted strain, nitrate utilization genes may have been independently acquired as indicated by adjacent phage mobility elements; these genes are also duplicated with each copy detected in separate genomic islands. These results provide direct evidence for nitrate utilization by Prochlorococcus and illuminate the complex evolutionary history of this trait.
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