A B S T R A C TPostharvest biological control agents as a viable alternative to the use of synthetic chemicals have been the focus of considerable research for the last 30 years by many scientists and several commercial companies worldwide. Several antagonists of postharvest pathogens have been identified and tested in laboratory, semi-commercial, and commercial settings and were developed into commercial products. The discovery and development of these antagonists into a product followed a paradigm in which a single antagonist isolated from one commodity was also expected to be effective on other commodities that vary in their genetic background, physiology, postharvest handling, and susceptibility to pathogens. In most cases, product development was successfully achieved but their full commercial potential was not realized. The low success rate of postharvest biocontrol products has been attributed to several problems, including difficulties in mass production and formulation of the antagonist, the physiological status of the harvested commodity and its susceptibility to specific pathogens. All these factors played a major role in the reduced and inconsistent performance of the biocontrol product when used under commercial conditions. Although many studies have been conducted on the mode of action of postharvest microbial antagonists, our understanding is still very incomplete. In this regard, a systems approach, that takes into account all the components of the biocontrol system, may represent the best approach to investigating the network of interactions that exist. Very little is known about the overall diversity and composition of microbial communities on harvested produce and how these communities vary across produce types, their function, the factors that influence the composition of the microbiota after harvest and during storage, and the distribution of individual taxa. In light of the progress made in recent years in metagenomic technologies, this technology should be used to characterize the composition of microbial communities on fruit and vegetables. Information on the dynamics and diversity of microbiota may be useful to developing a new paradigm in postharvest biocontrol that is based on constructing synthetic microbial communities that provide superior control of pathogens.

Lactoperoxidase is a member of the family of the mammalian heme peroxidases which have a broad spectrum of activity. Their best known effect is their antimicrobial activity that arouses much interest in in vivo and in vitro applications. In this context, the proper use of lactoperoxidase needs a good understanding of its mode of action, of the factors that favor or limit its activity, and of the features and properties of the active molecules. The first part of this review describes briefly the classification of mammalian peroxidases and their role in the human immune system and in host cell damage. The second part summarizes present knowledge on the mode of action of lactoperoxidase, with special focus on the characteristics to be taken into account for in vitro or in vivo antimicrobial use. The last part looks upon the characteristics of the active molecule produced by lactoperoxidase in the presence of thiocyanate and/or iodide with implication(s) on its antimicrobial activity.

Plant growth performance is optimized under hydroponic conditions. The comparison between aquaponics and hydroponics has attracted considerable attention recently, particularly regarding plant yield. However, previous research has not focused on the potential of using aquaponic solution complemented with mineral elements to commercial hydroponic levels in order to increase yield. For this purpose, lettuce plants were put into AeroFlo installations and exposed to hydroponic (HP), aquaponic (AP), or complemented aquaponic (CAP) solutions. The principal finding of this research was that AP and HP treatments exhibited similar (p > 0.05) plant growth, whereas the shoot weight of the CAP treatment showed a significant (p < 0.05) growth rate increase of 39% on average compared to the HP and AP treatments. Additionally, the root weight was similar (p > 0.05) in AP and CAP treatments, and both were significantly higher (p < 0.05) than that observed in the HP treatment. The results highlight the beneficial effect of recirculating aquaculture system (RAS) water on plant growth. The findings represent a further step toward developing decoupled aquaponic systems (i.e., two-or multi-loops) that have the potential to establish a more productive alternative to hydroponic systems. Microorganisms and dissolved organic matter are suspected to play an important role in RAS water for promoting plant roots and shoots growth.

The exo-beta-1,3-glucanase (EC 3.2.1.58) activity of Pichia anomala strain K, an antagonistic yeast of Botrytis cinerea on postharvest apples, was studied in a synthetic medium supplemented with laminarin, a cell wall preparation (CWP) of B. cinerea, or glucose. The highest enzyme activity was detected in culture media containing a CWP of B. cinerea as the sole carbon source, whereas the lowest activity was observed in culture media supplemented with glucose. Exoglc1, an exo-beta-1,3-glucanase, was purified to homogeneity from culture filtrates of strain K containing a CWP. The molecular mass of exoglc1 was estimated to be under 15 kDa. Optimum activity of exoglc1 was recorded at 50 degrees C and pH 5.5. The exoglc1 K(m) value was estimated at 22.4 mg/ml. Exoglc1 showed in vitro a stronger inhibitory effect on germ tube growth of B. cinerea than on conidia germination and caused morphological changes such as leakage of cytoplasm and cell swelling. Exo-beta-1,3-glucanase activity was detected on apples treated with strain K and was similar to exoglc1 on the basis of activity on native gel. Moreover, the addition of a CWP to a suspension of P. anomala stimulated both in situ exo-beta-1,3-glucanase activity and protective activity against the pathogen, strengthening the hypothesis that exo-beta-1,3-glucanase activity is one of the mechanisms of action involved in the suppression of B. cinerea by P. anomala strain K.