Anaerobic utilization of essential oils by denitrifying bacteria

Integrating the latest biological advances in the key steps of a food packaging life cycle

This literature review provides a focus on the potential of integrating the latest scientific and technological advances in the biological field to improve the status of the key steps of a food packaging life cycle: production, usage, post-usage, and long-term fate. A case study of such multi-biological food packaging is demonstrated based on the use of PHAs (polyhydroxyalkanoates) polymer, a microbiologically produced polymer from non-food renewable resources, activated by the use of bioactive components to enhance its usage benefits by reducing food loss and waste, displaying potential for reusability, compostability as post-usage, and finally, being ultimately biodegradable in most common natural conditions to considerably reduce the negative impact that persistent plastics have on the environment. We discuss how designing safe and efficient multi "bio" food packaging implies finding a compromise between sometimes contradictory functional properties. For example, active antimicrobials help preserve food but can hamper the ultimate biodegradation rate of the polymer. This review presents such antagonisms as well as techniques (e.g., coatings, nanoencapsulation) and tools (e.g., release kinetic) that can help design optimized, safe, and efficient active food packaging.

Microbial monoterpene transformations-a review

Isoprene and monoterpenes constitute a significant fraction of new plant biomass. Emission rates into the atmosphere alone are estimated to be over 500 Tg per year. These natural hydrocarbons are mineralized annually in similar quantities. In the atmosphere, abiotic photochemical processes cause lifetimes of minutes to hours. Microorganisms encounter isoprene, monoterpenes, and other volatiles of plant origin while living in and on plants, in the soil and in aquatic habitats. Below toxic concentrations, the compounds can serve as carbon and energy source for aerobic and anaerobic microorganisms. Besides these catabolic reactions, transformations may occur as part of detoxification processes. Initial transformations of monoterpenes involve the introduction of functional groups, oxidation reactions, and molecular rearrangements catalyzed by various enzymes. Pseudomonas and Rhodococcus strains and members of the genera Castellaniella and Thauera have become model organisms for the elucidation of biochemical pathways. We review here the enzymes and their genes together with microorganisms known for a monoterpene metabolism, with a strong focus on microorganisms that are taxonomically validly described and currently available from culture collections. Metagenomes of microbiomes with a monoterpene-rich diet confirmed the ecological relevance of monoterpene metabolism and raised concerns on the quality of our insights based on the limited biochemical knowledge.

Geraniol and geranial dehydrogenases induced in anaerobic monoterpene degradation by Castellaniella defragrans

Castellaniella defragrans is a Betaproteobacterium capable of coupling the oxidation of monoterpenes with denitrification. Geraniol dehydrogenase (GeDH) activity was induced during growth with limonene in comparison to growth with acetate. The N-terminal sequence of the purified enzyme directed the cloning of the corresponding open reading frame (ORF), the first bacterial gene for a GeDH (geoA, for geraniol oxidation pathway). The C. defragrans geraniol dehydrogenase is a homodimeric enzyme that affiliates with the zinc-containing benzyl alcohol dehydrogenases in the superfamily of medium-chain-length dehydrogenases/reductases (MDR). The purified enzyme most efficiently catalyzes the oxidation of perillyl alcohol (k(cat)/K(m) = 2.02 × 10(6) M(-1) s(-1)), followed by geraniol (k(cat)/K(m) = 1.57 × 10(6) M(-1) s(-1)). Apparent K(m) values of <10 μM are consistent with an in vivo toxicity of geraniol above 5 μM. In the genetic vicinity of geoA is a putative aldehyde dehydrogenase that was named geoB and identified as a highly abundant protein during growth with phellandrene. Extracts of Escherichia coli expressing geoB demonstrated in vitro a geranial dehydrogenase (GaDH) activity. GaDH activity was independent of coenzyme A. The irreversible formation of geranic acid allows for a metabolic flux from β-myrcene via linalool, geraniol, and geranial to geranic acid.

Persistency assessment and aerobic biodegradation of selected cyclic sesquiterpenes present in essential oils

Sesquiterpenes are ubiquitous in essential oils but an assessment of their environmental behavior is still required for their use as components of natural fragrance ingredients and oral care flavors. Persistency plays a key role in hazard and risk assessment, but the current knowledge on the biodegradation of sesquiterpenes in the aquatic environment is limited. This could have important consequences for the persistent, bioaccumulative and toxic (PBT) assessment of essential oils because most of the sesquiterpene components have a log K(OW) of >4.5 and are identified as potentially bioaccumulating according to REACH screening criteria. In the present study, a persistency screening assessment was conducted on 11 cyclic sesquiterpenes selected from 10 different families of sesquiterpenes characterized by their carbon skeleton. Current biodegradation prediction models (BioWin™, BioHCwin, and Catalogic) were found to be of limited use because most of the sesquiterpenes studied were outside the structural domain of the models. Aerobic biodegradation was measured in a standard or prolonged Organisation for Economic Co-operation and Development (OECD) 301F Manometric Respirometry test for ready biodegradability. α-Bisabolol, α-humulene, β-caryophyllene, α-cedrene, cedrol, longifolene, and δ-cadinene exceeded the pass level of 60% degradation and can be regarded as not persistent. Alpha-gurjunene, himachalenes (α, β, γ), and (-)-thujopsene almost achieved the pass level reaching between 51% and 56% ultimate biodegradation. Although germacrene D only achieved 24% ultimate biodegradation, specific analysis at the end of the test did indicate complete primary degradation. Given that the shape of the biodegradation curves indicates poor bioavailability and ready biodegradability tests are very stringent, it is expected that all the sesquiterpenes tested in the present study would be degraded under environmental conditions.

Linalool dehydratase-isomerase, a bifunctional enzyme in the anaerobic degradation of monoterpenes

Castellaniella (ex Alcaligenes) defragrans strain 65Phen mineralizes monoterpenes in the absence of oxygen. Soluble cell extracts anaerobically catalyzed the isomerization of geraniol to linalool and the dehydration of linalool to myrcene. The linalool dehydratase was present in cells grown on monoterpenes, but not if grown on acetate. We purified the novel enzyme ∼1800-fold to complete homogeneity. The native enzyme had a molecular mass of 160 kDa. Denaturing gel electrophoresis revealed one single protein band with a molecular mass of 40 kDa, which indicated a homotetramer as native conformation. The aerobically purified enzyme was anaerobically activated in the presence of 2 mm DTT. The linalool dehydratase catalyzed in vitro two reactions in both directions depending on the thermodynamic driving forces: a water secession from the tertiary alcohol linalool to the corresponding acyclic monoterpene myrcene and an isomerization of the primary allylalcohol geraniol in its stereoisomer linalool. The specific activities (V(max)) were 140 nanokatals mg(-1) for the linalool dehydratase and 410 nanokatals mg(-1) for the geraniol isomerase, with apparent K(m) values of 750 μm and 500 μm, respectively. The corresponding open reading frame was identified and revealed a precursor protein with a signal peptide for a periplasmatic location. The amino acid sequence did not affiliate with any described enzymes. We suggest naming the enzyme linalool dehydratase-isomerase according to its bifunctionality and placing it as a member of a new protein family within the hydrolyases (EC 4.2.1.X).

Evaluation of Essential Oil Antifungal Activity Against Mycorrhizal Fungi—The Case of Laurus Nobilis Essential Oil

Mycorrhiza is regarded essential for plant growth, especially in regions where precipitation and nutrient availability are low. Hundreds of aromatic plant species, which contain essential oils, are growing naturally around the Mediterranean. The plant essential oils are known for their antimicrobial properties. The aim of this study was to investigate whether the aromaticLaurus nobilis, abundant in the Mediterranean region, can influence the development of two mycorrhizal species,Glomus deserticolaandGlomus intraradices, and how this effect can influence the growth of the host plant. The major compounds ofL. nobilisessential oil were 1.8 cineole, sabinene, α-pinene, eugenole, α-terpinyl acetate, and β-pinene. Both mycorrhizal fungi colonized successfully the host plants, positively influencing their growth.G. deserticolapresented higher infection level thanG. intraradices.Addition ofL. nobilisoil into substrates resulted in mycorrhiza inhibition, and the level of inhibition was analogous with the amount of added essential oil. The fungi were benefited by the aromatic compounds up to 15 mg of essential oil per L of soil. However, 30 and 60 mg L-1of essential oil were able to create significant inhibition in mycorrhiza development and to restrict the host growth. Since the presence -of aromatics in the Mediterranean region could create such ecological problems, the elimination of aromatic plant litter before reforestation is suggested, to give the opportunity for mycorrhiza establishment and successful development of new plants.