Precursor-Directed Biosynthesis of Antialgal Fluorinated Bacillamide Derivatives in Bacillus atrophaeus

The bacillamides are a class of indole alkaloids produced by the Bacillus genus that possess significant antialgal activity. Incorporation of fluorine into the bacillamides was carried out using a precursor-directed biosynthesis approach, with 4-, 5-, and 6-fluorotryptophan added to growing cultures of Bacillus atrophaeus IMG-11. This yielded the corresponding fluorinated analogues of bacillamides A and C, in addition to new derivatives of the related metabolite N-acetyltryptamine, thus demonstrating a degree of plasticity in the bacillamide biosynthetic pathway. The bacillamide derivatives were tested for activity against bloom-forming algae, which revealed that fluorination could improve the antialgal activity of these compounds in a site-specific manner, with fluorination at the 6-position consistently resulting in improved activity.

Transcriptomics-guided identification of an algicidal protease of the marine bacterium Kordia algicida OT-1

In recent years, interest in algicidal bacteria has risen due to their ecological importance and their potential as biotic regulators of harmful algal blooms. Algicidal bacteria shape the plankton communities of the oceans by inhibiting or lysing microalgae and by consuming the released nutrients. Kordia algicida strain OT-1 is a model marine algicidal bacterium that was isolated from a bloom of the diatom Skeletonema costatum. Previous work has suggested that algicidal activity is mediated by secreted proteases. Here, we utilize a transcriptomics-guided approach to identify the serine protease gene KAOT1_RS09515, hereby named alpA1 as a key element in the algicidal activity of K. algicida. The protease AlpA1 was expressed and purified from a heterologous host and used in in vitro bioassays to validate its activity. We also show that K. algicida is the only algicidal species within a group of four members of the Kordia genus. The identification of this algicidal protease opens the possibility of real-time monitoring of the ecological impact of algicidal bacteria in natural phytoplankton blooms.

Targeted Isolation of Two New Anti-inflammatory and UV-A Protective Dipyrroloquinones from the Sponge-associated Fungus Aspergillus tamarii MCCF102

In following up on observed in vitro anti-inflammatory activity of the organic extract of the marine sponge-derived fungus Aspergillus tamarii MCCF102, two new dipyrrolobenzoquinones, terreusinone B and C (1: and 2: ), were discovered along with the known analogue, terreusinone (3: ). The structures of 1: -3: were determined by spectroscopic and spectrometric analyses, along with chemical inter-conversion. In vitro testing on lipopolysaccharide (LPS) stimulated RAW 264.7 murine macrophage cells revealed that 1: -3: exhibit anti-inflammatory activity by inhibiting nitric oxide production in a dose-dependent manner (IC₅₀ < 1 µM) without any cytotoxicity observed at the same concentrations. Due to this and the UV-A absorptive properties imparted by the highly conjugated structures of these molecules, the potential for using 1: -3: or related analogues as natural sunscreen components is suggested. Gene sequencing and informatics biosynthetic gene cluster comparisons were insufficient to confidently elucidate the biosynthetic origins of these compounds, possibly suggesting the occurrence of a gene cluster not detected in the initial sequencing or a non-canonical pathway that should be further investigated.

Metabolomics Benefits from Orbitrap GC-MS-Comparison of Low- and High-Resolution GC-MS

The development of improved mass spectrometers and supporting computational tools is expected to enable the rapid annotation of whole metabolomes. Essential for the progress is the identification of strengths and weaknesses of novel instrumentation in direct comparison to previous instruments. Orbitrap liquid chromatography (LC)–mass spectrometry (MS) technology is now widely in use, while Orbitrap gas chromatography (GC)–MS introduced in 2015 has remained fairly unexplored in its potential for metabolomics research. This study aims to evaluate the additional knowledge gained in a metabolomics experiment when using the high-resolution Orbitrap GC–MS in comparison to a commonly used unit-mass resolution single-quadrupole GC–MS. Samples from an osmotic stress treatment of a non-model organism, the microalga Skeletonema costatum, were investigated using comparative metabolomics with low- and high-resolution methods. Resulting datasets were compared on a statistical level and on the level of individual compound annotation. Both MS approaches resulted in successful classification of stressed vs. non-stressed microalgae but did so using different sets of significantly dysregulated metabolites. High-resolution data only slightly improved conventional library matching but enabled the correct annotation of an unknown. While computational support that utilizes high-resolution GC–MS data is still underdeveloped, clear benefits in terms of sensitivity, metabolic coverage, and support in structure elucidation of the Orbitrap GC–MS technology for metabolomics studies are shown here.

Simplifying the complex: metabolomics approaches in chemical ecology

Chemical signals are important mediators of organismal interactions. These interactions significantly influence ecosystem structure and thus are crucial to understand. Ecologists and analytical chemists work closely together to identify the specific molecules regulating ecological interactions. However, limitations in the analytical techniques on the one hand and time-demanding bioassays on the other have been restraining chemical ecology research. Application of metabolomics techniques has recently led to significant advancement of the field. Here, we discuss modifications to the traditional bioassay-guided fractionation approach with metabolomics techniques. We focus on two challenging topics within chemical ecology, waterborne cues and single-cell investigations, to highlight how metabolomics techniques can succeed where traditional approaches have failed. Graphical abstract ᅟ.

The making of a plankton toxin

A combined genetic and chemical study reveals the biosynthetic steps involved in making the toxin domoic acid

Karenia brevis allelopathy compromises the lipidome, membrane integrity, and photosynthesis of competitors

The formation, propagation, and maintenance of harmful algal blooms are of interest due to their negative effects on marine life and human health. Some bloom-forming algae utilize allelopathy, the release of compounds that inhibit competitors, to exclude other species dependent on a common pool of limiting resources. Allelopathy is hypothesized to affect bloom dynamics and is well established in the red tide dinoflagellate Karenia brevis. K. brevis typically suppresses competitor growth rather than being acutely toxic to other algae. When we investigated the effects of allelopathy on two competitors, Asterionellopsis glacialis and Thalassiosira pseudonana, using nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry (MS)-based metabolomics, we found that the lipidomes of both species were significantly altered. However, A. glacialis maintained a more robust metabolism in response to K. brevis allelopathy whereas T. pseudonana exhibited significant alterations in lipid synthesis, cell membrane integrity, and photosynthesis. Membrane-associated lipids were significantly suppressed for T. pseudonana exposed to allelopathy such that membranes of living cells became permeable. K. brevis allelopathy appears to target lipid biosynthesis affecting multiple physiological pathways suggesting that exuded compounds have the ability to significantly alter competitor physiology, giving K. brevis an edge over sensitive species.

Variable allelopathy among phytoplankton reflected in red tide metabolome

Harmful algae are known to utilize allelopathy, the release of compounds that inhibit competitors, as a form of interference competition. Competitor responses to allelopathy are species-specific and allelopathic potency of producing algae is variable. In the current study, the biological variability in allelopathic potency was mapped to the underlying chemical variation in the exuded metabolomes of five genetic strains of the red tide dinoflagellate Karenia brevis using ¹H nuclear magnetic resonance (NMR) spectroscopy. The impacts of K. brevis allelopathy on growth of a model competitor, Asterionellopsis glacialis, ranged from strongly inhibitory to negligible to strongly stimulatory. Unique metabolomes of K. brevis were visualized as chemical fingerprints, suggesting three distinct metabolic modalities - allelopathic, non-allelopathic, and stimulatory - with each modality distinguished from the others by different concentrations of several metabolites. Allelopathic K. brevis was characterized by enhanced concentrations of fatty acid-derived lipids and aromatic or other polyunsaturated compounds, relative to less allelopathic K. brevis. These findings point to a previously untapped source of information in the study of allelopathy: the chemical variability of phytoplankton, which has been underutilized in the study of bloom dynamics and plankton chemical ecology.

Chemical ecology of marine plankton

Covering: January 2013 to online publication December 2014This review summarizes recent research in the chemical ecology of marine pelagic ecosystems, and aims to provide a comprehensive overview of advances in the field in the time period covered. In order to highlight the role of chemical cues and toxins in plankton ecology this review has been organized by ecological interaction types starting with intraspecific interactions, then interspecific interactions (including facilitation and mutualism, host-parasite, allelopathy, and predator-prey), and finally community and ecosystem-wide interactions.