Chemical polymorphism in defense secretions during ontogenetic development of the millipede Niponia nodulosa

Exploration and utilization of novel aldoxime, nitrile, and nitro compounds metabolizing enzymes from plants and arthropods

Aldoxime (R1R2C=NOH) and nitrile (R-C≡N) are nitrogen-containing compounds that are found in species representing all kingdoms of life. The enzymes discovered from the microbial "aldoxime-nitrile" pathway (aldoxime dehydratase, nitrile hydratase, amidase, and nitrilase) have been thoroughly studied because of their industrial importance. Although plants utilize cytochrome P450 monooxygenases to produce aldoxime and nitrile, many biosynthetic pathways are yet to be studied. Cyanogenic millipedes accumulate various nitrile compounds, such as mandelonitrile. However, no such aldoxime- and nitrile-metabolizing enzymes have been identified in millipedes. Here, I review the exploration of novel enzymes from plants and millipedes with characteristics distinct from those of microbial enzymes, the catalysis of industrially useful reactions, and applications of these enzymes for nitrile compound production.

After chemo-metamorphosis: p-menthane monoterpenoids characterize the oil gland secretion of adults of the oribatid mite, Nothrus palustris

The oil gland secretion of the oribatid mite Nothrus palustris is known to show the phenomenon of juvenile-adult polymorphism, i.e., juvenile instars produce secretions predominated by geranial, whereas adults secrete dehydrocineole along with a number of chemically unidentified compounds. We here re-analyzed the secretions of adult N. palustris by GC-MS and NMR spectroscopy, eventually identifying the unknown compounds as p-menthane monoterpenoids. The major components were two isomeric 6-isopropenyl-3-methyl-cyclohex-3-en-1-yl formates (= p-1,8-menthadien-5-yl formates), which accounted for about 75% of the secretion. These were accompanied by five additional, only partly identified p-menthanes (or p-methane-derivatives), all of which represented minor or trace components. In addition, adult secretions contained two C21-hydrocarbons, 1,12-heneicosadiene (major) and a heneicosatriene (minor). Menthane monoterpenoids represent a novel sub-class of terpene compounds in the oil gland secretions of Oribatida. In case of N. palustris, we assume that both geranial and p-menthane monoterpenoids arise via the mevalonate pathway which obviously shows a split at the level of geranyl pyrophosphate, leading to geranial in juveniles and to p-menthanes in adults. The significance of methane occurrence in oil glands as well as the taxonomic distribution of juvenile-adult polymorphism in oribatid oil gland secretions is discussed. The latter phenomenon-i.e., "chemo-metamorphosis" of secretions-is not known from early- and middle-derivative Oribatida nor from Astigmata, but appears to be more common in some derivative desmonomatan and brachypyline oribatid groups.

Polymorphic scent gland secretions in Nelima harvestmen: “Sclerosomatid compounds” but different chemical lineages

The scent glands of harvestmen (Opiliones) produce secretions of taxon-specific composition. One class of compounds, assumed to be a key group in opilionid chemosystematics and prevalent among sclerosomatid Eupnoi, was termed “sclerosomatid compounds” (SCs). Known compounds of this group comprise acyclic 4-methyl-branched ethyl-ketones and -alcohols as well as 2,4-dimethyl-branched primary alcohols and aldehydes, originally described from several species of North American Leiobuninae. We analyzed the scent gland secretions of Nelima ssp. (Sclerosomatidae, Leiobuninae) from two continents by gas chromatography-mass spectrometry, NMR, stereoselective synthesis, and chiral chromatography. We found a surprising chemical dichotomy: while North American N. paesserli produced typical acyclic SCs such as (E)-4-methyl-4-hexen-3-one, the secretions of European Nelima species exhibited a mixture of aromatic and aliphatic compounds, namely (R)-2-methyl-1-phenyl-pentan-3-one (MPP), 4-phenyl-2-butanone (PB), 2-phenylacetamide (PA), as well as (2R,4R)-2,4-dimethylhexanoic acid (DHA), all of which are new for the secretions of harvestmen. Remarkably, in N. sempronii, the secretions of juveniles (containing PB) differed from the secretions of adults (containing MPP and DHA). Though the chemistry of European Nelima species clearly diverged at first sight, all compounds detected either possess specific chemical motifs that allow an assignment to the class of SCs or appear to be biochemically/ontogenetically connected to SC-components. Thus, we here add novel compounds to the pool of SCs along with an extension of the definition of SCs to include aromatic compounds with SC-motifs. Furthermore, we describe a first case of juvenile-adult polymorphism for the exocrine secretions of harvestmen and provide a scheme of how secretions are regenerated.

Production of Plant-Associated Volatiles by Select Model and Industrially Important Streptomyces spp

The Streptomyces produce a great diversity of specialized metabolites, including highly volatile compounds with potential biological activities. Volatile organic compounds (VOCs) produced by nine Streptomyces spp., some of which are of industrial importance, were collected and identified using gas chromatography–mass spectrometry (GC-MS). Biosynthetic gene clusters (BGCs) present in the genomes of the respective Streptomyces spp. were also predicted to match them with the VOCs detected. Overall, 33 specific VOCs were identified, of which the production of 16 has not been previously reported in the Streptomyces. Among chemical classes, the most abundant VOCs were terpenes, which is consistent with predicted biosynthetic capabilities. In addition, 27 of the identified VOCs were plant-associated, demonstrating that some Streptomyces spp. can also produce such molecules. It is possible that some of the VOCs detected in the current study have roles in the interaction of Streptomyces with plants and other higher organisms, which might provide opportunities for their application in agriculture or industry.

HCN emission by a Polydesmid Millipede Detected Remotely by Reactive Adsorption on Gold Nanoparticles Followed by Laser Desorption/Ionization Mass Spectrometry (LDI-MS)

Hydrocyanic acid (HCN) is a well-known defensive allomone in the chemical arsenal of millipedes in the order Polydesmida. The presence of HCN in the headspace vapor of adult Xystocheir dissecta (Wood, 1867), a common millipede from the San Francisco Bay Area, was traced by laser desorption/ionization-mass spectrometry (LDI-MS). To accomplish this, the headspace vapor surrounding caged, live millipedes was allowed to diffuse passively over gold-nanoparticle (AuNP) deposits placed at various distances from the emitting source. The stainless steel plates with AuNP deposits were removed and irradiated by a 355-nm laser. The gaseous ions generated in this way were detected by time-of-flight mass spectrometry. The intensity of the mass spectrometric peak detected at m/z 249 for the Au(CN)₂^- complex anion was compared to that of the residual Au^- signal (m/z 197). Using this procedure, HCN vapors produced by the live millipedes could be detected up to 50 cm away from the source. Furthermore, the addition of H₂O₂, as an internal oxygen source for the gold cyanidation reaction that takes place in the AuNP deposits, significantly increased the detection sensitivity. Using the modified H₂O₂ addition procedure, HCN could now be detected at 80 cm from the source. Moreover, we found a decreasing intensity ratio of the Au(CN)₂^-/Au^- signals as the distance from the emitting source increased, following an exponential-decay distribution as predicted by Fick's law of diffusion. Graphical abstract.

Genomes of trombidid mites reveal novel predicted allergens and laterally transferred genes associated with secondary metabolism

Background

Trombidid mites have a unique life cycle in which only the larval stage is ectoparasitic. In the superfamily Trombiculoidea ("chiggers"), the larvae feed preferentially on vertebrates, including humans. Species in the genus Leptotrombidium are vectors of a potentially fatal bacterial infection, scrub typhus, that affects 1 million people annually. Moreover, chiggers can cause pruritic dermatitis (trombiculiasis) in humans and domesticated animals. In the Trombidioidea (velvet mites), the larvae feed on other arthropods and are potential biological control agents for agricultural pests. Here, we present the first trombidid mites genomes, obtained both for a chigger, Leptotrombidium deliense, and for a velvet mite, Dinothrombium tinctorium.

Results

Sequencing was performed using Illumina technology. A 180 Mb draft assembly for D. tinctorium was generated from two paired-end and one mate-pair library using a single adult specimen. For L. deliense, a lower-coverage draft assembly (117 Mb) was obtained using pooled, engorged larvae with a single paired-end library. Remarkably, both genomes exhibited evidence of ancient lateral gene transfer from soil-derived bacteria or fungi. The transferred genes confer functions that are rare in animals, including terpene and carotenoid synthesis. Thirty-seven allergenic protein families were predicted in the L. deliense genome, of which nine were unique. Preliminary proteomic analyses identified several of these putative allergens in larvae.

Conclusions

Trombidid mite genomes appear to be more dynamic than those of other acariform mites. A priority for future research is to determine the biological function of terpene synthesis in this taxon and its potential for exploitation in disease control.

Identification of saturated and unsaturated 1-methoxyalkanes from the Thai millipede Orthomorpha communis as potential "Raincoat Compounds"

Mixtures of saturated and unsaturated 1-methoxyalkanes (alkyl methyl ethers, representing more than 45.4% of the millipede hexane extracts) were newly identified from the Thai polydesmid millipede, Orthomorpha communis, in addition to well-known polydesmid defense allomones (benzaldehyde, benzoyl cyanide, benzoic acid, mandelonitrile, and mandelonitrile benzoate) and phenolics (phenol, o- and p-cresol, 2-methoxyphenol, 2-methoxy-5-methylphenol and 3-methoxy-4-methylphenol). The major compound was 1-methoxy-n-hexadecane (32.9%), and the mixture might function as “raincoat compounds” for the species to keep off water penetration and also to prevent desiccation.

Cyanogenesis in Arthropods: From Chemical Warfare to Nuptial Gifts

Chemical defences are key components in insect⁻plant interactions, as insects continuously learn to overcome plant defence systems by, e.g., detoxification, excretion or sequestration. Cyanogenic glucosides are natural products widespread in the plant kingdom, and also known to be present in arthropods. They are stabilised by a glucoside linkage, which is hydrolysed by the action of β-glucosidase enzymes, resulting in the release of toxic hydrogen cyanide and deterrent aldehydes or ketones. Such a binary system of components that are chemically inert when spatially separated provides an immediate defence against predators that cause tissue damage. Further roles in nitrogen metabolism and inter- and intraspecific communication has also been suggested for cyanogenic glucosides. In arthropods, cyanogenic glucosides are found in millipedes, centipedes, mites, beetles and bugs, and particularly within butterflies and moths. Cyanogenic glucosides may be even more widespread since many arthropod taxa have not yet been analysed for the presence of this class of natural products. In many instances, arthropods sequester cyanogenic glucosides or their precursors from food plants, thereby avoiding the demand for de novo biosynthesis and minimising the energy spent for defence. Nevertheless, several species of butterflies, moths and millipedes have been shown to biosynthesise cyanogenic glucosides de novo, and even more species have been hypothesised to do so. As for higher plant species, the specific steps in the pathway is catalysed by three enzymes, two cytochromes P450, a glycosyl transferase, and a general P450 oxidoreductase providing electrons to the P450s. The pathway for biosynthesis of cyanogenic glucosides in arthropods has most likely been assembled by recruitment of enzymes, which could most easily be adapted to acquire the required catalytic properties for manufacturing these compounds. The scattered phylogenetic distribution of cyanogenic glucosides in arthropods indicates that the ability to biosynthesise this class of natural products has evolved independently several times. This is corroborated by the characterised enzymes from the pathway in moths and millipedes. Since the biosynthetic pathway is hypothesised to have evolved convergently in plants as well, this would suggest that there is only one universal series of unique intermediates by which amino acids are efficiently converted into CNglcs in different Kingdoms of Life. For arthropods to handle ingestion of cyanogenic glucosides, an effective detoxification system is required. In butterflies and moths, hydrogen cyanide released from hydrolysis of cyanogenic glucosides is mainly detoxified by β-cyanoalanine synthase, while other arthropods use the enzyme rhodanese. The storage of cyanogenic glucosides and spatially separated hydrolytic enzymes (β-glucosidases and α-hydroxynitrile lyases) are important for an effective hydrogen cyanide release for defensive purposes. Accordingly, such hydrolytic enzymes are also present in many cyanogenic arthropods, and spatial separation has been shown in a few species. Although much knowledge regarding presence, biosynthesis, hydrolysis and detoxification of cyanogenic glucosides in arthropods has emerged in recent years, many exciting unanswered questions remain regarding the distribution, roles apart from defence, and convergent evolution of the metabolic pathways involved.

Step-wise evolution of complex chemical defenses in millipedes: a phylogenomic approach

With fossil representatives from the Silurian capable of respiring atmospheric oxygen, millipedes are among the oldest terrestrial animals, and likely the first to acquire diverse and complex chemical defenses against predators. Exploring the origin of complex adaptive traits is critical for understanding the evolution of Earth's biological complexity, and chemical defense evolution serves as an ideal study system. The classic explanation for the evolution of complexity is by gradual increase from simple to complex, passing through intermediate "stepping stone" states. Here we present the first phylogenetic-based study of the evolution of complex chemical defenses in millipedes by generating the largest genomic-based phylogenetic dataset ever assembled for the group. Our phylogenomic results demonstrate that chemical complexity shows a clear pattern of escalation through time. New pathways are added in a stepwise pattern, leading to greater chemical complexity, independently in a number of derived lineages. This complexity gradually increased through time, leading to the advent of three distantly related chemically complex evolutionary lineages, each uniquely characteristic of each of the respective millipede groups.

Joannsin, a novel Kunitz-type FXa inhibitor from the venom of Prospirobolus joannsi

The repugnatorial glands of millipedes release various defensive chemical secretions. Although varieties of such defensive secretions have been studied, none of them is protein or peptide. Herein, a novel factor Xa (FXa) inhibitor named joannsin was identified and characterised from repugnatorial glands of Prospirobolus joannsi. Joannsin is composed of 72 amino acid residues including six cysteines, which form three intra-molecular disulfide bridges. It is a member of Kunitz-type protease inhibitor family, members of which are also found in the secretory glands of other arthropods. Recombinant joannsin exhibited remarkable inhibitory activity against trypsin and FXa with a Ki of 182.7 ± 14.6 and 29.5 ± 4.7 nM, respectively. Joannsin showed strong anti-thrombosis functions in vitro and in vivo. Joannsin is the first peptide component in millipede repugnatorial glands to be identified and is a potential candidate and/or template for the development of anti-thrombotic agents. These results also indicated that there is Kunitz-type protease inhibitor toxin in millipede repugnatorial glands as in other arthropods secretory glands.

A novel cytochrome P450, CYP3201B1, is involved in (R)-mandelonitrile biosynthesis in a cyanogenic millipede

Specialized arthropods and more than 2500 plant species biosynthesize hydroxynitriles and release hydrogen cyanide as a defensive mechanism. The millipede Chamberlinius hualienensis accumulates (R)-mandelonitrile as a cyanide precursor. Although biosynthesis of hydroxynitriles in cyanogenic plants and in an insect are extensively studied, (R)-mandelonitrile biosynthesis in cyanogenic millipedes has remained unclear. In this study, we identified the biosynthetic precursors of (R)-mandelonitrile and an enzyme involved in (R)-mandelonitrile biosynthesis. Using deuterium-labelled compounds, we revealed that (E/Z)-phenylacetaldoxime and phenylacetonitrile are the biosynthetic precursors of (R)-mandelonitrile in the millipede as well as other cyanogenic organisms. To identify the enzymes involved in (R)-mandelonitrile biosynthesis, 50 cDNAs encoding cytochrome P450s were cloned and coexpressed with yeast cytochrome P450 reductase in yeast, as cytochrome P450s are involved in the biosynthesis of hydroxynitriles in other cyanogenic organisms. Among the 50 cytochrome P450s from the millipede, CYP3201B1 produced (R)-mandelonitrile from phenylacetonitrile but not from (E/Z)-phenylacetaldoxime, whereas plant and insect cytochrome P450s catalysed the dehydration of aldoximes and hydroxylation of nitriles. CYP3201B1 is not phylogenetically related to cytochrome P450s from other cyanogenic organisms, indicating that hydroxynitrile biosynthetic cytochrome P450s have independently evolved in distant species. Our study will shed light on the evolution of cyanogenesis among plants, insects and millipedes.

DATABASE

Nucleotide sequence data are available in the DDBJ/EMBL/GenBank databases under the accession numbers LC125356-LC125405.