Biosynthesis of the algal pheromone fucoserratene by the freshwater diatom Asterionella formosa (Bacillariophyceae)

Chemical Diversity of Headspace and Volatile Oil Composition of Two Brown Algae (Taonia atomaria and Padina pavonica) from the Adriatic Sea

Two selected brown algae (Taonia atomaria and Padina pavonica from the family Dictyotaceae, order Dictyotales) growing in the same area (island Vis, central Adriatic Sea) were collected at the same time. Their phytochemical composition of the headspace volatile organic compounds (HS-VOCs; first time report) was determined by headspace solid-phase microextraction (HS-SPME). Hydrodistillation was applied for the isolation of their volatile oils (first report on T. atomaria volatile oil). The isolates were analyzed by gas chromatography (GC-FID) and mass spectrometry (GC-MS). The headspace and oil composition of T. atomaria were quite similar (containing germacrene D, epi-bicyclosesquiphellandrene, β-cubebene and gleenol as the major compounds). However, P. pavonica headspace and oil composition differed significantly (dimethyl sulfide, octan-1-ol and octanal dominated in the headspace, while the oil contained mainly higher aliphatic alcohols, trans-phytol and pachydictol A). Performed research contributes to the knowledge of the algae chemical biodiversity and reports an array of different compounds (mainly sesquiterpenes, diterpenes and aliphatic compounds); many of them were identified in both algae for the first time. Identified VOCs with distinctive chemical structures could be useful for taxonomic studies of related algae.

Phytochemical study of the headspace volatile organic compounds of fresh algae and seagrass from the Adriatic Sea (single point collection)

Performed phytochemical study contributes to the knowledge of volatile organic compounds (VOCs) of Halopteris filicina (Grateloup) Kützing, Dictyota dichotoma (Hudson) J. V. Lamouroux, Posidonia oceanica (L.) Delile and Flabellia petiolata (Turra) Nizamuddin from the Adriatic Sea (single point collection). VOCs were investigated by headspace solid-phase microextraction (HS-SPME) and analysed by gas chromatography and mass spectrometry (GC-MS/FID). H. filicina headspace contained dimethyl sulfide (DMS; 12.8%), C8-compounds (e.g. fucoserratene (I; 9.5%)), benzaldehyde (II; 8.7%), alkane C17, dictyopterene D and C (III, IV), tribromomethane (V), 1-iodopentane, others. F. petiolata headspace was characterized by DMS (22.2%), 6-methylhept-5-en-2-one (9.5%), C17 (9.1%), II (6.5%), compounds I-V. DMS (59.3%), C15 (14.5%), C17 (7.2%) and C19 (6.3%) dominated in P. oceanica headspace. Sesquiterpenes were found in D. dichotoma, predominantly germacrene D (28.3%) followed by other cadinenyl (abundant), muurolenyl and amorphenyl structures. Determined VOCs may be significant for chemosystematics and chemical communications in marine ecosystem.

The role of algae and cyanobacteria in the production and release of odorants in water

This review covers literatures pertaining to algal and cyanobacterial odor problems that have been published over the last five decades. Proper evaluation of algal and cyanobacterial odors may help establish removal strategies for hazardous metabolites while enhancing the recyclability of water. A bloom of microalgae is a sign of an anthropogenic disturbance in aquatic systems and can lead to diverse changes in ecosystems along with increased production of odorants. In general, because algal and cyanobacterial odors vary in chemistry and intensity according to blooming pattern, it is necessary to learn more about the related factors and processes (e.g., changes due to differences in taxa). This necessitates systematic and transdisciplinary approaches that require the cooperation of chemists, biologists, engineers, and policy makers.

Intraspecific chemical communication in microalgae

Contents 516 I. 516 II. 518 III. 518 IV. 521 V. 523 VI. 523 VII. 526 526 References 526 SUMMARY: The relevance of infochemicals in the relationships between organisms is emerging as a fundamental aspect of aquatic ecology. Exchanges of chemical cues are likely to occur not only between organisms of different species, but also between conspecific individuals. Especially intriguing is the investigation of chemical communication in microalgae, because of the relevance of these organisms for global primary production and their key role in trophic webs. Intraspecific communication between algae has been investigated mostly in relation to sexuality and mating. The literature also contains information on other types of intraspecific chemical communication that have not always been explicitly tagged as ways to communicate to conspecifics. However, the proposed role of certain compounds as intraspecific infochemicals appears questionable. In this article, we make use of this plethora of information to describe the various instances of intraspecific chemical communication between conspecific microalgae and to identify the common traits and ecological significance of intraspecific communication. We also discuss the evolutionary implications of intraspecific chemical communication and the mechanisms by which it can be inherited. A special focus is the genetic diversity among conspecific algae, including the possibility that genetic diversity is an absolute requirement for intraspecific chemical communication.

Selective growth promotion of bloom-forming raphidophyte Heterosigma akashiwo by a marine bacterial strain

Algal bloom is typically caused by aberrant propagation of a single species, resulting in its predomination in the local population. While environmental factors including temperature and eutrophication are linked to bloom, the precise mechanism of its formation process is still obscure. Here, we isolated a bacterial strain that promotes growth of Heterosigma akashiwo, a Raphidophyceae that causes harmful algal blooms. Based on 16S rRNA gene sequence, the strain was identified as Altererythrobacter ishigakiensis, a member of the class Alphaproteobacteria. When added to culture, this strain facilitated growth of H. akashiwo and increased its cell culture yield significantly. Importantly, this strain did not affect the growth of other raphidophytes, Chattonella ovate and C. antiqua, indicating that it promotes growth of H. akashiwo in a species-specific manner. We also found that, in co-culture, H. akashiwo suppressed the growth of C. ovate. When A. ishigakiensis was added to the mixed culture, H. akashiwo growth was facilitated while C. ovate propagation was markedly suppressed, indicating that the presence of the bacterium enhances the dominance of H. akashiwo over C. ovate. This is the first example of selective growth promotion of H. akashiwo by a marine bacterium, and may exemplify importance of symbiotic bacterium on algal bloom forming process in general.

Quorum sensing is a language of chemical signals and plays an ecological role in algal-bacterial interactions

Algae are ubiquitous in the marine environment, and the ways in which they interact with bacteria are of particular interest in marine ecology field. The interactions between primary producers and bacteria impact the physiology of both partners, alter the chemistry of their environment, and shape microbial diversity. Although algal-bacterial interactions are well known and studied, information regarding the chemical-ecological role of this relationship remains limited, particularly with respect to quorum sensing (QS), which is a system of stimuli and response correlated to population density. In the microbial biosphere, QS is pivotal in driving community structure and regulating behavioral ecology, including biofilm formation, virulence, antibiotic resistance, swarming motility, and secondary metabolite production. Many marine habitats, such as the phycosphere, harbour diverse populations of microorganisms and various signal languages (such as QS-based autoinducers). QS-mediated interactions widely influence algal-bacterial symbiotic relationships, which in turn determine community organization, population structure, and ecosystem functioning. Understanding infochemicals-mediated ecological processes may shed light on the symbiotic interactions between algae host and associated microbes. In this review, we summarize current achievements about how QS modulates microbial behavior, affects symbiotic relationships, and regulates phytoplankton chemical ecological processes. Additionally, we present an overview of QS-modulated co-evolutionary relationships between algae and bacterioplankton, and consider the potential applications and future perspectives of QS.

Low-Molecular-Weight Metabolites from Diatoms: Structures, Biological Roles and Biosynthesis

Diatoms are abundant and important biological components of the marine environment that biosynthesize diverse natural products. These microalgae are rich in various lipids, carotenoids, sterols and isoprenoids, some of them containing toxins and other metabolites. Several groups of diatom natural products have attracted great interest due to their potential practical application as energy sources (biofuel), valuable food constituents, and prospective materials for nanotechnology. In addition, hydrocarbons, which are used in climate reconstruction, polyamines which participate in biomineralization, new apoptotic agents against tumor cells, attractants and deterrents that regulate the biochemical communications between marine species in seawaters have also been isolated from diatoms. However, chemical studies on these microalgae are complicated by difficulties, connected with obtaining their biomass, and the influence of nutrients and contaminators in their environment as well as by seasonal and climatic factors on the biosynthesis of the corresponding natural products. Overall, the number of chemically studied diatoms is lower than that of other algae, but further studies, particularly those connected with improvements in the isolation and structure elucidation technique as well as the genomics of diatoms, promise both to increase the number of studied species with isolated biologically active natural products and to provide a clearer perception of their biosynthesis.

Interactions between diatoms and bacteria

Diatoms and bacteria have cooccurred in common habitats for hundreds of millions of years, thus fostering specific associations and interactions with global biogeochemical consequences. Diatoms are responsible for one-fifth of the photosynthesis on Earth, while bacteria remineralize a large portion of this fixed carbon in the oceans. Through their coexistence, diatoms and bacteria cycle nutrients between oxidized and reduced states, impacting bioavailability and ultimately feeding higher trophic levels. Here we present an overview of how diatoms and bacteria interact and the implications of these interactions. We emphasize that heterotrophic bacteria in the oceans that are consistently associated with diatoms are confined to two phyla. These consistent bacterial associations result from encounter mechanisms that occur within a microscale environment surrounding a diatom cell. We review signaling mechanisms that occur in this microenvironment to pave the way for specific interactions. Finally, we discuss known interactions between diatoms and bacteria and exciting new directions and research opportunities in this field. Throughout the review, we emphasize new technological advances that will help in the discovery of new interactions. Deciphering the languages of diatoms and bacteria and how they interact will inform our understanding of the role these organisms have in shaping the ocean and how these interactions may change in future oceans.

A reactive conjugated allene involved in the biosynthesis of volatile oxylipins in the moss Dicranum scoparium

We addressed the role of the unusual acetylenic fatty acid dicranin as a precursor for volatile oxylipins in the moss Dicranum scoparium. Dicranin is transformed immediately after mechanical wounding of moss tissue to volatile C5- and C6-oxylipins. The transformation of synthetic deuterium labeled dicranin was monitored using LC/MS analysis and multivariate statistics to identify polar metabolites produced during volatile formation. Among the newly formed oxylipins is a highly reactive conjugated C13 allene with similar degrees of labeling compared to the C5 volatiles suggesting that it results as second cleavage product from the biosynthesis of pentenal and pentenone.

LIPOXYGENASE PRODUCTS IN MARINE DIATOMS: A CONCISE ANALYTICAL METHOD TO EXPLORE THE FUNCTIONAL POTENTIAL OF OXYLIPINS(1)

Oxylipins are oxygenated derivatives of polyunsaturated fatty acids (PUFAs) that act as chemical mediators in many ecological and physiological processes in marine and freshwater diatoms. The occurrence and distribution of these molecules are relatively widespread within the lineage with considerable species-specific differences due to the variability of both the fatty acids recognized as substrates and the enzymatic transformations. The present review provides a general introduction to recent studies on diatom oxylipins and describes an analytical method for the detection and assessment of these elusive molecules in laboratory and field samples. This methodology is based on selective enrichment of the oxylipin fraction by solvent extraction, followed by parallel acquisition of full-scan UV and tandem mass spectra on reverse phase liquid chromatography (LC) peaks. The analytical procedure enables identification of potential genetic differences, enzymatic regulation, and ecophysiological conditions that result in different oxylipin signatures, thus providing an effective tool for probing the functional relevance of this class of lipids in plankton communities. Examples of oxylipin measurements in field samples are also provided as a demonstration of the analytical potential of the methodology.

15S-lipoxygenase metabolism in the marine diatom Pseudo-nitzschia delicatissima

In recent years, oxylipins (lipoxygenase-derived oxygenated fatty acid products) have been reported in several bloom-forming marine diatoms. Despite increasing attention on the ecophysiological role of these molecules in marine environments, their biosynthesis is largely unknown in these microalgae. Biochemical methods, including tandem mass spectrometry, nuclear magnetic resonance and radioactive probes were used to identify structures, enzymatic activities and growth-dependent modulation of oxylipin biosynthesis in the pennate diatom Pseudo-nitzschia delicatissima. Three major compounds, 15S-hydroxy-(5Z,8Z,11Z,13E,17Z)-eicosapentaenoic acid (15S-HEPE), 15-oxo-5Z,9E,11E,13E-pentadecatetraenoic acid and 13,14-threo-13R-hydroxy-14S,15S-trans-epoxyeicosa-5Z,8Z,11Z,17Z-tetraenoic acid (13,14-HEpETE), were produced by three putative biochemical pathways triggered by eicosapentaenoic acid-dependent 15S lipoxygenase. Oxylipin production increases along the growth curve, with remarkable changes that precede the demise of the culture. At least one of the compounds, namely 15-oxoacid, is formed only in the stationary phase immediately before the collapse of the culture. Synthesis and regulation of phyco-oxylipins seem to correspond to a signaling mechanism that governs adaptation of diatoms along the growth curve until bloom termination. Factors triggering the process are unknown but synthesis of 15-oxoacid, constrained within a time-window of a few days just before the collapse of the culture, implies the involvement of a physiological control not directly dependent on distress or death of diatom cells.

Diatom/copepod interactions in plankton: the indirect chemical defense of unicellular algae

Numerous coexisting species can be observed in the open oceans. This includes the complex community of the plankton, which comprises all free floating organisms in the sea. Traditionally, nutrient limitation, competition, predation, and abiotic factors have been assumed to shape the community structure in this environment. Only in recent years has the idea arisen that chemical signals and chemical defense can influence species interactions in the plankton as well. Key players at the base of the marine food web are diatoms (unicellular algae with silicified cell walls) and their main predators, the herbivorous copepods. It was assumed that diatoms represent a generally good food source for the grazers but recent work indicates that some species use chemical defenses. Secondary metabolites, released by these algae immediately after wounding, are targeted not against the predators themselves but rather at interfering with their reproductive success. This strategy allows diatoms to reduce the grazer population, thereby influencing the marine food web. This review addresses the chemical ecology of the defensive oxylipins formed by diatoms and the question of how these metabolites can act in such a dilute environment. Aspects of biosynthesis, bioassays, and the possible implications of such a chemical defense for the plankton community structure are also discussed.

Aquatic taste and odor: a primary signal of drinking-water integrity

Aquatic taste and odor (T/O) is rarely produced by toxic contaminants or pathogens; nevertheless, it has major negative impacts on the public and the drinking-water industry. Consumers use T/O as a primary measure of drinking water safety, yet this criterion is poorly understood, and its origins and triggers often go untraced. Much surface-water T/O is produced by the increased production of volatile organic compounds (VOCs) by algae. These chemicals can be symptomatic of short-term problems with source, treatment, or distribution systems. At a broader level, they can signify fundamental changes in aquatic ecosystems induced by human activity. T/O varies in chemistry, intensity, and production patterns among different algal taxa, and is often linked with excessive algal growth and/or the invasion of noxious species. Some VOCs may signal the presence of potentially toxic algae and/or other associated water quality issues. Traditionally, T/O has been linked with the widespread eutrophication of many surface waters; however, there has been a recent growth in the number of T/O events reported in oligo-mesotrophic systems, for example, the Glenmore Reservoir (Calgary AB) and the Laurentian Great Lakes. From a management and public perspective, therefore, it is vitally important to monitor T/O, and to continue to work toward a better understanding of the proximal and the ultimate causes-which VOCs and algae species are involved. In the short term, odor events could be anticipated and water treatment optimized. In the long term, this approach would contribute toward more a robust management of this resource through remedial or preventative measures.