Cyclic hydroxamic acid accumulation in corn seedlings exposed to reduced water potentials before,during, and after germination

Cyclic hydroxamic acids are innate compounds associated with pest resistance in several grass species. The major cyclic hydroxamic acids of com, 2,4-dihydroxy-7-methoxy-2H-1,4-benzoxazin-3-one (DIMBOA) and 2,4-dihydroxy-3H-1,4-benzoxazin-3-one (DIBOA), were measured in seedlings after exposure to various water stress treatments. Both DIMBOA and DIBOA were found in greater quantities in plants experiencing a water deficit stress than in nonstressed plants. The increased cyclic hydroxamic acid coincided with a reduction in seedling growth, suggesting that cyclic hydroxamic acids are stress metabolites. Plants grown under conditions that restrict growth, such as water deficit stress, contain higher cyclic hydroxamic acids, which should make them more resistant to herbivorous pests and pathogenic microorganisms.     

Soil transformation of wheat and corn metabolites mboa and DIM2BOA into aminophenoxazinones

The defensive cyclic hydroxamates 7-methoxy-2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIMBOA) and 7,8-dimethoxy-2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIM₂BOA) of wheat and corn are transformed in nonsterile soil, via 6-methoxy-2(3H)-benzoxazolone (MBOA) and 6,7-dimethoxy-2(3H)-benzoxazolone (M₂BOA) respectively, into 2-amino-7-methoxy-3H-phenoxazin-3-one and 2-amino-4,6,7-trimethoxy-3H-phenoxazin-3-one. The soil transformation is similar of that undergone by the rye metabolite 2(3H)-benzoxazolone (BOA) into 2-amino-3H-phenoxazin-3-one. The transformations to phenoxazinones are not observed in sterile soil. The 2-amino-3H-phenoxazin-3-one inhibits barnyard grass radicle elongation, but the methoxylated aminophenoxazinones are not significantly inhibitory.     

Toxicokinetics of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) in the European corn borer,Ostrinia nubilalis (Hübner)

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), the major hydroxamic acid present in corn, and its tritiated derivative, were prepared synthetically for use in the determination of the toxicokinetics of this insect deterrent in the European corn borer (ECB),Ostrinia nubilalis. In growth studies with DIMBOA (0, 0.05, 0.2, and 0.5 mg/g diet), the mean time to pupation and adult emergence were significantly lengthened by an increase in concentration. Pupal and adult weights, for both female and male, decreased with an increase in concentration. Increased larval and pupal mortality occurred at the highest concentration of DIMBOA. DIMBOA, at concentrations of 0.2 and 0.5 mg/g diet, resulted in a decrease in the number of egg masses produced per female, and at 0.5 mg/g diet, in a decrease in the number of eggs per egg mass. Larvae fed from the neonate stage on a diet containing 0.2 mg [³H]- + [¹H]DIMBOA/g diet showed an increase in the content of label from fourth to fifth instar, but levels declined at pupation and emergence. A large amount of the labeled compounds was excreted by the insect in the pupal case. In dose-related studies, both uptake and excretion increased with an increase in concentration of DIMBOA (0.05, 0.2, 0.4 mg/g diet), while a body burden (concentration in the tissues/concentration in the frass) of approximately 0.25 was maintained for all concentrations. At the highest dose of DIMBOA (0.4 mg/g), the ECB increased consumption, possibly to compensate for the toxic effects of the compound. In topical application studies, elimination of the labeled compound in the frass was rapid, reaching 65% by 4 hr and 88% by 48 hr. Accumulation of label in tissues other than hemolymph was low. The results show that the ECB does possess adaptive mechanisms to deal with the effects of this host-derived compound.     

Effects of fertility on biomass,phytotoxicity, and allelochemical content of cereal rye

Studies were conducted to evaluate biomass production, tissue phytotoxicity, and allelochemical content of rye (Secale cereale L.) shoots grown in three fertility regimes (low, medium or high) in the greenhouse. Wheeler rye or a polyculture of rye and hairy vetch (Vicia villosa Roth) grown with high fertility produced the greatest biomass (78.7 and 82.7 g), with the lowest root-to-shoot ratio (0.22 and 0.43) produced in the high-fertility treatments. The polyculture treatment grown with low fertility had a greater proportion of hairy vetch (18%) than when grown with high fertility (6%). Rye shoot residue phototoxicity was affected by fertility regime. Radicle elongation of cress (Lepidium sativum L.) and barnyardgrass [Enchinochloa crus-galli (L.) Beauv. I was inhibited by rye shoot residues in a modified Parker bioassay. Rye shoot residue grown with low fertility was less inhibitory to cress radicle elongation than rye residue from the medium- or high-fertility regimes. Extracts of dried rye shoots grown with high fertility were less inhibitory than extracts from other fertility regimes. The concentrations of ether extracts of rye causing 50% inhibition (I₅₀) of cress radicle elongation were between 125 and 276 µg/ml for greenhouse-grown and 60 and 138 µg/ml for the field-grown rye shoots. The major phytotoxic compounds in the rye shoot extracts were identified as DIBOA and BOA. The concentration of DIBOA in the greenhouse-grown rye shoots ranged between 128 and 423 µg/g while BOA concentration ranged between 2.5 and 31 µg/g. DIBOA and BOA levels were lowest in rye shoots grown with high fertility. Correlations between rye shoot biomass, DIBOA and BOA concentration, and cress barnyardgrass radicle length were significant.     

CHANGES OVER TIME IN THE ALLELOCHEMICAL CONTENT OF TEN CULTIVARS OF RYE (<Emphasis Type="Italic">Secale cereale</Emphasis> L.)

Published studies focused on characterizing the allelopathy-based weed suppression by rye cover crop mulch have provided varying and inconsistent estimates of weed suppression. Studies were initiated to examine several factors that could influence the weed suppressiveness of rye: kill date, cultivar, and soil fertility. Ten cultivars of rye were planted with four rates of nitrogen fertilization, and tissue from each of these treatment combinations was harvested three times during the growing season. Concentrations of a known rye allelochemical DIBOA (2,4-dihydroxy-1,4-(2H)benzoxazine-3-one) were quantified from the harvested rye tissue using high performance liquid chromatography (HPLC). Phytotoxicity observed from aqueous extracts of the harvested rye tissue correlated with the levels of DIBOA recovered in harvested tissue. The amount of DIBOA in rye tissue varied depending on harvest date and rye cultivar, but was generally lower with all cultivars when rye was harvested later in the season. However, the late maturing variety Wheeler retained greater concentrations of DIBOA in comparison to other rye cultivars when harvested later in the season. The decline in DIBOA concentrations as rye matures, and the fact that many rye cultivars mature at different rates may help explain why estimates of weed suppression from allelopathic agents in rye have varied so widely in the literature.     

Distribution and Exudation of Allelochemicals in Wheat Triticum aestivum

Wheat allelopathy has potential for weed suppression. Allelochemicals were identified in wheat seedlings, and they were exuded from seedlings into agar growth medium. p-Hydroxybenzoic, trans-p-coumaric, cis-p-coumaric, syringic, vanillic, trans-ferulic, and cis-ferulic acids and 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) were identified in both the shoots and roots of 17-day-old wheat seedlings and their associated agar growth medium. Wheat accessions with previously identified allelopathic activity tended to contain higher levels of allelochemicals than poorly allelopathic ones. The allelopathic compounds present in the shoots generally also were identified in the roots and in the agar medium. Allelochemicals were distributed differentially in wheat, with roots normally containing higher levels of allelochemicals than the shoots. When the eight allelochemicals were grouped into benzoic acid and cinnamic acid derivatives, DIMBOA, total coumaric, and total ferulic acids, the amount of each group of allelochemicals was correlated between the roots and the shoots. Most of the allelochemicals identified in the shoots and roots could be exuded by the living roots of wheat seedling into the agar growth medium. However, the amounts of allelochemicals in the agar growth medium were not proportional to those in the roots. Results suggest that wheat plants may retain allelochemicals once synthesized. The presence of allelochemicals in the agar growth medium demonstrated that wheat seedlings were able to synthesize and to exude phytotoxic compounds through their root system that could inhibit the root growth of annual ryegrass.     

Role of benzoxazinones in allelopathy by rye (Secale cereale L.)

Two phytotoxic compounds [2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) and 2(3H)-benzoxazolinone (BOA)] were previously isolated and identified in 35-day-old greenhouse-grown rye shoot tissue. Both compounds were also detected by TLC in greenhouse-grown root and fieldgrown shoot tissue. The concentration of DIBOA varied in the tissues, with the greatest quantity detected in greenhouse-grown shoots. DIBOA and BOA were compared with -phenyllactic acid (PLA) and -hydroxybutyric acid (HBA) for activity on seed germination and seedling growth and were consistently more toxic than either compound. Dicot species tested, including lettuce (Lactuca sativa L.), tomato (Lycopersicon esculentum Mill.), and redroot pigweed (Amaranthus retroflexus L.), were 30% more sensitive than the monocots tested. Of the two benzoxazinone compounds, DIBOA was most toxic to seedling growth. DIBOA and BOA reduced chlorophyll production inChlamydomonas rheinhardtii Dangeard, by 50% at 7.5 × 10^–5 M and 1.0 × 10^–3 M, respectively. Both DIBOA and BOA inhibited emergence of barnyardgrass (Echinochloa crusgalli L. Beauv.), cress (Lepidium sativum L.), and lettuce when applied to soil, indicating their potential for allelopathic activity.Journal Article No. 11945 of the Michigan Agricultural Experiment Station.     

2,2′-OXO-1, 1 ′-azobenzene A microbially transformed allelochemical from 2,3-Benzoxazolinone: I

2,2-Oxo-1,1 -azobenzene (AZOB), a compound with strong herbicidal activity, was isolated and characterized from a soil supplemented with 2,3-benzoxazolinone (BOA). A parallel experiment with 6-methoxy-2,3-benzoxazolinone (MBOA) yielded AZOB as well as its mono-(MAZOB) and dimethoxy-(DIMAZOB) derivatives. These compounds were produced only in the presence of soil microorganisms, via possible intermediates, I and II, which may dimerize or react with the parent molecule to form the final products. In the case of MBOA, it was shown that demethoxylation precedes the oxidation step. Although BOA and 2,4-dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA) were leached out of rye residues, there were no detectable amounts of the biotransformation products in the soil. When BOA was mixed with soil and rye residue, either under field conditions or in vitro, AZOB was detected. Levels of free BOA in the soil were greatly reduced by incubation with rye residue. AZOB was more toxic to curly cress (Lepidium sativum L.) and barnyardgrass (Echinochloa crusgatti L.) than either DIBOA or BOA.Journal Article No. 12943 of the Michigan Agricultural Experiment Station.     

Effect of Dimboa, a Hydroxamic Acid from Cereals, on Peroxisomal and Mitochondrial Enzymes from Aphids: Evidence for the Presence of Peroxisomes in Aphids

2,4-Dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA), a hydroxamic acid involved in the resistance of cereals to aphids, was administered to adult individuals of the aphid Sitobion avenae in artificial diets. Effects on the cellular metabolism were inferred from the evaluation of several organelle marker enzymes. Catalase from peroxisomes and cytochrome c oxidase from mitochondria increased their activities about twofold when aphids were fed with 2 mM DIMBOA. The role of these enzymes in the metabolizing of xenobiotics by aphids is discussed. Biochemical and cytochemical evidences for the presence of peroxisomes in aphids are reported here for the first time.     

2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one (N-O-Me-DIMBOA), a possible toxic factor in corn to the southwestern corn borer

The southwestern corn borer (SWCB),Diatraea grandiosella Dyar, is a major pest of corn,Zea mays L., in the southern United States. The damage to corn is caused primarily by larval feeding on leaf, ear, and stem tissues. In this study, 2-hydroxy-4,7-dimethoxy-1,4-benzoxazin-3-one (N-O-Me-DIMBOA) was identified by MS and NMR as present in corn whorl surface waxes. This compound has evidently not been isolated previously, but its glucoside has been reported in corn, wheat, andCoix lachryma. It is present in the waxes in a higher concentration than DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one) and 6-MBOA (6-methoxybenzoxazolinone). It was toxic to the SWCB in a stress diet, but it was less toxic to this insect than 6-MBOA when incorporated in the standard rearing diet. Nevertheless, it may have some role in the resistance of corn to the SWCB because the total surface wax content is higher in resistant lines than in susceptible lines.Mention of a trademark, proprietary product, or vendor does not constitute a guarantee or warranty of the product by the U.S. Department of Agriculture and does not imply its approval to the exclusion of other products or vendors that may also be suitable.     

Allelochemicals in wheat (Triticum aestivum L.): production and exudation of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one

An analytical technique employing gas chromatography and tandem mass spectrometry (GC/MS/MS) was employed to systematically screen fifty-eight wheat accessions for their differential production of 2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one (DIMBOA) from three consecutive sources, i.e., the shoots, roots, and in the associated agar growth medium (collected as root exudates) of 17-day-old wheat seedlings. DIMBOA content differed significantly in the shoots, roots, or in the agar growth medium between accessions. DIMBOA accumulated differentially within the plant, with roots containing more DIMBOA than the shoots. Only 19% of accessions were able to exude DIMBOA from living roots into their growth medium, indicating the exudation of DIMBOA is accession-specific. DIMBOA level in root tissues is expected to be high when a high level of DIMBOA content is detected in the shoots. Wheat seedlings did not release detectable amounts of DIMBOA when the DIMBOA level was low in the root tissues. The valuable genetic material with high levels of DIMBOA in the shoots or roots identified in the present research could be used to breed for wheat cultivars with elevated allelopathic activity.     

Hydroxamic acid glucosides in honeydew of aphids feeding on wheat

DIMBOA glucoside (2-O-/gb-D-glucopyranosyl-4-hydroxy-7-meth-oxy-1,4-benzoxazin-3-one), the main hydroxamic acid (Hx) in intact wheat plants, was detected in the honey dew ofRhopalosiphum padi feeding on seedlings of six wheat cultivars that differed in their concentration of Hx, suggesting that the chemical circulates in the phloem. Neither the aglucone (DIMBOA) nor its main breakdown product were found in any of the honeydew samples. Honey dew production by aphids caged on seedlings of the wheat cultivars and DIMBOA glucoside concentrations in the honeydew followed biphasic curves when plotted against Hx concentration, suggesting passive ingestion of the chemical from the phloem at low Hx concentrations and limited ingestion due to feeding deterrency by Hx in mesophyll cells at high Hx concentrations. The presence of plant toxins such as Hx glucosides in the phloem sap, the main ingesta of aphids, and in the mesophyll cells, has major implications for plant defense, through a feeding deterrent effect during stylet penetration, and deterrency (antixenosis) along with antibiosis during feeding.     

Using Generic Pheromone Lures to Expedite Identification of Aggregation Pheromones for the Cerambycid Beetles Xylotrechus nauticus, Phymatodes lecontei, and Neoclytus modestus modestus

Males of several species of longhorned beetles in the subfamily Cerambycinae produce sex or aggregation pheromones consisting of 2,3-hexanediols and/or hydroxyhexanones. We tested the hypothesis that this diol/hydroxyketone pheromone motif is highly conserved within the subfamily, and the resulting prediction that multiple cerambycine species will be attracted to compounds of this type. We also tested the concept that live traps baited with generic blends of these compounds could be used as a source of live insects from which pheromones could be collected and identified. Traps placed in a mature oak woodland and baited with generic blends of racemic 2-hydroxyhexan-3-one and 3-hydroxyhexan-2-one captured adults of both sexes of three cerambycine species: Xylotrechus nauticus (Mannerheim), Phymatodes lecontei Linsley, and Phymatodes decussatus decussatus (LeConte). Odors collected from male X. nauticus contained a 9:1 ratio of two male-specific compounds, (R)- and (S)-3-hydroxyhexan-2-one. Field trials with synthetic compounds determined that traps baited with (R)-3-hydroxyhexan-2-one (94% ee), alone or in blends with other isomers, attracted similar numbers of X. nauticus of both sexes, whereas (S)-3-hydroxyhexan-2-one (94% ee) attracted significantly fewer beetles. Phymatodes lecontei and P. d. decussatus also were caught in traps baited with hydroxyhexanones, as well as a few specimens of two other cerambycine species, Neoclytus modestus modestus Fall (both sexes) and Brothylus gemmulatus LeConte (only females). Male N. m. modestus produced (R)-3-hydroxyhexan-2-one, which was not present in extracts from females. Neoclytus m. modestus of both sexes also responded to lures that included (R)-3-hydroxyhexan-2-one as one of the components. The only male-specific compound found in extracts from P. lecontei was (R)-2-methylbutan-1-ol, and adults of both sexes were attracted to racemic 2-methylbutan-1-ol in field bioassays. Surprisingly, P. lecontei of both sexes also were attracted to (R)- and (S)-3-hydroxyhexan-2-ones, although neither compound was detected in extracts from this species. Males of all five beetle species had gland pores on their prothoraces that were similar in structure to those that have been associated with volatile pheromone production in other cerambycine species. The attraction of multiple cerambycine species of two tribes to (R)-3-hydroxyhexan-2-one in this study, and in earlier studies with other cerambycine species, suggests that this compound is a widespread aggregation pheromone component in this large and diverse subfamily. Overall, the attraction of multiple species from different cerambycine tribes to this compound at a single field site supports the hypothesis that the hydroxyketone pheromone structural motif is highly conserved within this subfamily.     

Possible Mechanism of Inhibition of 6-Methoxy-Benzoxazolin-2(3H)-One on Germination of Cress (Lepidium sativum L.)

6-Methoxy-benzoxazolin-2(3H)-one (MBOA) inhibited the germination of cress (Lepidium sativum L.) seeds at concentrations greater than 0.03 mM. Inhibition was overcome by sucrose, suggesting that MBOA may inhibit sugar metabolism in cress seeds. Induction of α-amylase activity in seeds was also inhibited by MBOA at concentrations greater than 0.03 mM. Inhibition of both germination and induction of α-amylase activity increased with increasing concentrations of MBOA, and the extent of germination correlated positively with the activity of α-amylase in the seeds. MBOA added to a reaction mixture for α-amylase assay did not affect enzyme activity, indicating that MBOA does not inhibit in vitro α-amylase activity. Cress seeds germinated approximately 16 hr after incubation, and inhibition of α-amylase by MBOA occurred within 6 hr after incubation. These results suggest that MBOA may inhibit the germination of cress seeds by inhibiting the induction of α-amylase activity, because α-amylase plays a key role in the conversion of reserve carbohydrate into soluble sugars, a prerequisite for seed germination.     

Identification and Synthesis of the Sex Pheromone of the Madeira Mealybug, <Emphasis Type="Italic">Phenacoccus Madeirensis</Emphasis> Green

Two components were identified from aeration extracts of the virgin female Madeira mealybug, Phenacoccus madeirensis as trans-(1R,3R)-chrysanthemyl (R)-2-methylbutanoate and (R)-lavandulyl (R)-2-methylbutanoate (with a ratio of 3:1) by a combination of gas chromatography retention time matches, mass spectrometry, and microchemical tests. The structures and chirality of the compounds were confirmed by comparing with synthetic compounds. The synthetic trans-(1R,3R)-chrysanthemyl (R)-2-methylbutanoate was highly attractive to males in laboratory bioassays; the synthetic (R)-lavandulyl (R)-2-methylbutanoate was weakly attractive. No synergistic effect was observed when the mixture of the two compounds was tested.     

Male-specific EAD active compounds produced by female European chafer Rhizotrogus majalis (Razoumowsky)

Chemical investigation of a fmale balloon-like organ of the European chafer, Rhizotrogus majalis (Razoumowsky), with GC-EAD has resulted in the identification of female-specific compounds, (R)-3- hydroxybutan-2-one, (2R,3R)-2,3-butanediol, and meso-2,3-butanediol that are specifically EAD-active with male antennae. No behavioral role for any of the EAD active compounds could be discerned with this species.     

Allelochemicals fromPolygonum sachalinense Fr. Schm. (Polygonaceae)

The root exudates fromPolygonum sachalinense in a recirculating system significantly inhibited lettuce seedling growth. The rhizomes and roots ofP. sachalinense were extracted with 80% acetone. Bioassay of the neutral-acidic fraction on the TLC agar plate showed the inhibitory activity corresponded to the two yellow pigment bands. Two orange needles were isolated and identified as anthraquinone compounds: emodin and physcion. Both compounds exhibited inhibitory activities against the seedling growth of several testing plant species. Glucosides were isolated fromP. sachalinense and were identified as emodin-1-O-β-D-glucoside and physcion-1-O-β-D-glucoside, respectively. On plant growth bioassay, these glucosides showed no phytotoxic activity against lettuce seedlings. The concentrations of emodin, physcion, and their glucosides from rhizome with roots, aerial parts, fallen leaves, and soil were determined. The rhizome with roots and fallen leaves contained emodin and physcion at relatively high concentrations. Emodin also occurs in the soil of this plant community with effective concentrations in the fall. The results indicate that these anthraquinones are responsible for the observed interference and are potent allelopathic substances.     

2,2′-OXO-1,1′-azobenzene: Selective toxicity of rye (Secale cereale L.) allelochemicals to weed and crop species: II

Three allelochemicals from rye or its breakdown products were evaluated for activity on garden cress (Lepidum sativum L.), barnyardgrass [Echinochloa crus-galli (L.) Beauv.], cucumber (Cucumis sativus L.), and snap bean (Phaseolus vulgaris L.). 2,4-Dihydroxy-1,4(2H)-benzoxazin-3-one (DIBOA), 2(3H)-benzoxazolinone (BOA), and 2,2-oxo-1,1-azobenzene (AZOB) were all applied singly at 50, 100, and 200 ppm and in two- and three-way combinations each at 50 and 100 ppm. AZOB at 100 and 200 ppm produced 38–49% more inhibition than DIBOA, while combinations of BOA/ DIBOA, which contained AZOB at 100 ppm had 54–90% more inhibition when compared to DIBOA/BOA combinations. All combinations were slightly antagonistic to barnyardgrass, while several combinations caused a synergistic response to garden cress germination and growth. Cucumbers and snap beans exhibited both types of responses, depending on the allelochemical combination and application rate. The plant-produced benzoxazinones were more inhibitory to crops than weeds. Therefore, improved herbicidal selectivity would be expected if there were rapid transformation of the benzoxazinones to the microbially produced AZOB.     

Effect of DIMBOA,an aphid resistance factor in wheat,on the aphid predatorEriopis connexa Germar (Coleoptera: Coccinellidae)

DIMBOA (2,4-dihydroxy-7-methoxy-1,4-benzoxazin-3-one), a secondary metabolite found in cereal extracts, confers resistance in wheat to aphids. Its effect on beneficial organisms was tested on larvae of the aphid predatorEriopis connexa Germar. Larvae were fed until pupation on artificial diets to which different concentrations of DIMBOA (2–200g/g diet) were added, as well as on aphids that had been feeding on wheat seedlings with different DIMBOA levels (140–440 g/g fresh tissue). In diets, the effect of DIMBOA was greatest on survival of third-instar larvae and on the duration of the second and fourth instars. When aphids were provided as food, those that had fed on a wheat cultivar with an intermediate DIMBOA level led to a significantly longer larval duration in the predator than did those that fed on either low or high DIMBOA cultivars. Shortest predator development times were obtained with aphid prey that had fed on high DIMBOA seedlings. Higher DIMBOA levels in the plant appear to reduce aphid feeding rates (and rates of DIMBOA ingestion), decreasing aphid survival and minimizing the effect of the toxin on the predator.On leave from Departamento de Entomologia, Universidad Nacional Agraria La Molina, Apartado aéreo 456, Lima, Perú.     

Volatile ketones from interdigital glands of black-tailed deer,Odocileus hemionus columbianus

Three volatile ketones, 2-tridecanone, (E)-3-tridecen-2-one and (E)-4-tridecen-2-one were identified in interdigital gland extracts from black-tailed deer,Odocoileus hemionus columbianus. The major compound, (E)-3-tridecen-2-one, inhibited the growth of several species of fungi and grampositive bacteria. The bacterium,Propionibacterium acnes, and the fungus,Trichophyton mentagrophytes required a minimum concentration (MIC) of 12.5 µg/ml and 25 µg/ml, respectively, for inhibition, (E)-3-Tridecen-2-one represents a new class of lipid antibiotics found on animal skin. The second major compound is this secretion, 2-tridecanone, was not active against any of the organisms tested.