Inners and biocontrol models

Techniques of modelling and simulation are discussed as they relate to bioengineering systems. The advantages and disadvantages of different analytical engineering methods utilized to gather information concerning the behavior of complex physiological and neuromuscular control mechanisms are explained. An Inners Criterion is developed to determine if the roots of a model lie within a certain “biologically realistic region” Γ_B, in the complex plane which contains the roots of linearized models for a large variety of neuromuscular systems. Several algorithmic methods based on the Jury Inners Test are described which specify whether the model roots lie within the desired region, thereby providing an indication as to the validity of the proposed model. This technique can help to eliminate tedious simulation on an unrealistic model with roots lying far outside this region. An exemplary model for control of vergence eye movements is presented and shown to satisfy the Γ_B criterion; several counter-examples are also discussed. The Inners approach can be adapted to other classes of bioengineering systems by specifying the region based on models that are contained in the class of interest.     

Use of endophytes as biocontrol agents

Plant diseases, caused by various microorganisms, including viruses, bacteria, fungi, protozoa and nematodes, affect agricultural practices and result in significant crop losses. Fungal pathogens are the major cause of plant diseases and infect most plants. Agrochemicals play a significant role in plant disease management to ensure a sustainable and productive agricultural system. However, the intensive use of chemicals has adverse effects on humans and ecosystem functioning and also reduces agricultural sustainability. A sustainable agriculture is achieved through reduction or elimination of fertilizers and agrochemicals, resulting in minimal impact to the environment. Recently, the use of antagonistic endophytes as biocontrol agents is drawing special attention as an attractive option for management of some plant diseases, resulting in minimal impact to the environment. Endophytes that resides asymptomatically within a plant, have the potential to provide a source of candidate strains for potential biocontrol applications. This review addresses biocontrol methods using endophytic fungi such as Colletotrichum, Cladosporium, Fusarium, Pestalotiopsis and Trichoderma species as an attractive option for management of some plant diseases. Potential endophytes are screened in vitro and in vivo to test their antagonistic actions by different mechanisms, including mycoparasitism, production of lytic enzymes and/or antibiotics and induction of plant defenses. Currently, efforts are being made to commercialize these biocontrol agents. A continued research pipeline consisting of screening, in vitro and in vivo testing, biomass production and commercialization of endophytes as biocontrol agents may contribute to sustainable agriculture.     

Improvement of Trichoderma strains for biocontrol

The use of the fungal genus Trichoderma to control fungal plant diseases is a promising alternative to the use of chemical compounds. The aim of this work has been to obtain Trichoderma strains with improved capacity as biological control agents. To do so, the hydrolytic capacity on fungal cell walls of strains of the fungus Trichoderma harzianum has been increased. On one hand, transformation experiments with genes which coded for chitinases and glucanases have been carried out in T. harzianumstra ins. On the other hand, the medium composition has also been modified in order to eliminate proteolytic degradation of some of the overproduced enzymes. Finally, hybrid chitinolytic enzymes with substrate-binding domains have been produced as an alternative to obtain improved biocontrol strains. The transformant strains, when compared with the wild type, showed improved antifungal capacity against the phytopathogenic fungus Rhizoctonia solani, in in vitro experiments.     

Bacteriophage biocontrol in wastewater treatment

Waterborne bacterial pathogens in wastewater remains an important public health concern, not only because of the environmental damage, morbidity and mortality that they cause, but also due to the high cost of disinfecting wastewater by using physical and chemical methods in treatment plants. Bacteriophages are proposed as bacterial pathogen indicators and as an alternative biological method for wastewater treatment. Phage biocontrol in large scale treatment requires adaptive and aggressive phages that are able to overcome the environmental forces that interfere with phage–host interactions while targeting unwanted bacterial pathogens and preventing biofilms and foaming. This review will shed light on aspects of using bacteriophage programming technology in wastewater plants to rapidly target and reduce undesirable bacteria without harming the useful bacteria needed for biodegradation.     

铜绿假单胞菌生防菌株抑菌代谢产物及其生防应用研究进展

微生物次生代谢产物的研究对开发微生物源农药具有重要意义。近年来一系列根际来源的铜绿假单胞菌被分离和鉴定,因其产生抑菌次生代谢产物,具有很好的生物防治效果。本文将系统综述铜绿假单胞菌生防菌株的种类及其抑菌代谢产物的多样性,并进一步介绍铜绿假单胞菌生防菌株的抑菌代谢产物合成机制及其遗传改造,简要讨论铜绿假单胞菌生防菌株抑菌代谢产物在生物防治上的应用和前景。     

Engineered bacteriophages as programmable biocontrol agents

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Antibiotic production by bacterial biocontrol agents

Interest in biological control of plant pathogens has been stimulated in recent years by trends in agriculture towards greater sustainability and public concern about the use of hazardous pesticides. There is now unequivocal evidence that antibiotics play a key role in the suppression of various soilborne plant pathogens by antagonistic microorganisms. The significance of antibiotics in biocontrol, and more generally in microbial interactions, often has been questioned because of the indirect nature of the supporting evidence and the perceived constraints to antibiotic production in rhizosphere environments. Reporter gene systems and bio-analytical techniques have clearly demonstrated that antibiotics are produced in the spermosphere and rhizosphere of a variety of host plants. Several abiotic factors such as oxygen, temperature, specific carbon and nitrogen sources, and microelements have been identified to influence antibiotic production by bacteria biocontrol agents. Among the biotic factors that may play a determinative role in antibiotic production are the plant host, the pathogen, the indigenous microflora, and the cell density of the producing strain. This review presents recent advances in our understanding of antibiotic production by bacterial biocontrol agents and their role in microbial interactions. This revised version was published online in August 2006 with corrections to the Cover Date.     

荧光假单胞菌生防机理的研究进展

荧光假单胞菌是植物根际促生细菌(Plant Growth Promoting Rhizobacteria,PGPR)具有分布广、数量多、营养需要简单、繁殖快、竞争定殖力强的特点。它们能通过产生多种次生代谢物及有效的根际定殖防治植物病害,成为植物生防控制的重要研究对象。主要论述了荧光假单胞菌对植物病害生物防治机理的研究进展。     

Bacteriophages as biocontrol agents of food pathogens

Bacteriophages have long been recognized for their potential as biotherapeutic agents. The recent approval for the use of phages of Listeria monocytogenes for food safety purposes has increased the impetus of phage research to uncover phage-mediated applications with activity against other food pathogens. Areas of emerging and growing significance, such as predictive modelling and genomics, have shown their potential and impact on the development of new technologies to combat food pathogens. This review will highlight recent advances in the research of phages that target food pathogens and that promote their use in biosanitation, while it will also discuss its limitations.     

Natural wine yeasts as biocontrol agents

A total of 586 natural wine yeasts, belonging to different genera, were tested for their antagonistic effect on fungal pathogens. A low percentage of yeast strains completely inhibited the pathogens and the biocontrol activity was found to be a strain characteristic and did not solely depend on species or genus. Among the antagonists, two strains of Saccharomyces cerevisiae and one of Zygosaccharomyces showed a broad spectrum of antagonistic activity against 10 fungal pathogens.     

Flower color affects tri-trophic-level biocontrol interactions

The adults of many parasitoid species require nectar for optimal fitness, but very little is known of flower recognition. Flight cage experiments showed that the adults of an egg parasitoid (Trichogramma carverae Oatman and Pinto) benefited from alyssum (Lobularia maritima L.) bearing white flowers to a greater extent than was the case for light pink, dark pink or purple flowered cultivars, despite all cultivars producing nectar. Survival and realised parasitism on all non-white flowers were no greater than when the parasitoids were caged on alyssum shoots from which flowers had been removed. The possibility that differences between alyssum cultivars were due to factors other than flower color, such as nectar quality, was excluded by dying white alyssum flowers by placing the roots of the plants in 5% food dye (blue or pink) solution. Survival of T. carverae was lower on dyed alyssum flowers than on undyed white flowers. Mixing the same dyes with honey in a third experiment conducted in the dark showed that the low level of feeding on dyed flowers was unlikely to be the result of olfactory or gustatory cues. Flower color appears, therefore, to be a critical factor in the choice of plants used to enhance biocontrol, and is likely also to be a factor in the role parasitoids play in structuring invertebrate communities.     

Governance of genetic biocontrol technologies for invasive fish

The modification of living agents for biological control can be collectively regarded as genetic biocontrol (GBC). Applications to invasive fish are an area of significant work in GBC, employing a diversity of techniques. Some of these techniques are governed by particular legislation, policy or treaty, (e.g., transgenesis), while others deliver agents with similar properties with minimal regulation. Together, this heterogeneity of governance and biology creates a number of challenges for effective use of GBC. In some cases, there are gaps and inconsistencies that pose real threats to biodiversity, and the long term sustainability of oversight arrangements as they currently stand is questionable. Researchers and would-be users of GBC for invasive fish must proactively engage with a variety of stakeholders to improve governance (in fish and other taxa), which we contend may include reconfiguration of relevant national governance systems, meaningful stakeholder dialogue and the creation of a new international treaty dedicated to biological control.     

Development of a broad-host-range phage cocktail for biocontrol

The aims of this study were to investigate the incidence of different resistance mechanisms to phage K in a bank of Irish Staph aureus hospital strains; and to develop a broad host-range phage cocktail with enhanced lytic activity against those strains which were previously phage resistant. A bank of 180 Staph aureus strains, which included all the sequence types currently in existence in Ireland, were tested for sensitivity to phage K. Twenty nine strains were identified, which did not permit plaque formation. The phage resistance systems in the 29 strain were investigated and it was found that restriction modification (r-m) was evident in 24, an adsorption inhibition mechanism was evident in three, while two were resistant by an unidentified mechanism. Seventeen modified derivatives of phage K were developed which could circumvent all the r-m systems. Nevertheless, six of the modified phage were considered superior in terms of their individual host ranges. These six were pooled as a cocktail with phage K, which then lysed 24 of the 29 resistant strains (97.2% of the entire staphylococcal bank). In conclusion, phage resistant systems affecting phage K are common in Staph. aureus but it is possible to significantly broaden the host-range of this phage for biocontrol applications.     

Bacteriophage-based biocontrol of biological sludge bulking in wastewater

In a previous paper, the first ever application of lytic bacteriophage (virus)-mediated biocontrol of biomass bulking in the activated sludge process using Haliscomenobacter hydrossis as a model filamentous bacterium was demonstrated. In this work we extended the biocontrol application to another predominant filamentous bacterium, Sphaerotilus natans, notoriously known to cause filamentous bulking in wastewater treatment systems. Very similar to previous study, one lytic bacteriophage was isolated from wastewater that could infect S. natans and cause lysis. Significant reduction in sludge volume index and turbidity of the supernatant was observed in batches containing S. natans biomass following addition of lytic phages. Microscopic examination confirmed that the isolated lytic phage can trigger the bacteriolysis of S. natans. This extended finding further strengthens our hypothesis of bacteriophage-based biocontrol of overgrowth of filamentous bacteria and the possibility of phage application in activated sludge processes, the world's widely used wastewater treatment processes.