Production of the biocontrol agent Pantoea agglomerans strain CPA-2 using commercial products and by-products

Evaluating the efficacy of microbial antagonists in inducing resistance, promoting growth, and providing biological control against powdery mildew in wheat

This study evaluates the biocontrol efficacy of three bacterial strains (Pseudomonas fluorescens DTPF-3, Bacillus amyloliquefaciens DTBA-11, and Bacillus subtilis DTBS-5) and two fungal strains (Trichoderma harzianum Pusa-5SD and Aspergillus niger An-27) antagonists, along with their combinations at varying doses (5.0, 7.5, and 10.0 g/kg of seeds), against wheat powdery mildew. The most effective dose (10 g/kg seeds) was further analyzed for its impact on induced resistance and plant growth promotion under greenhouse conditions. The study measured defense enzyme activities, biochemical changes, and post-infection plant growth metrics. All tested microbial antagonists at 10 g/kg significantly reduced PM severity, with B. subtilis strain DTBS-5 outperforming others in reducing PM severity and achieving the highest biocontrol efficacy. It was followed by B. amyloliquefaciens strain DTBA-11 and P. fluorescens strain DTPF-3, with the fungal antagonists showing no significant effect. Wheat crops treated with B. subtilis strain DTBS-5 exhibited substantial increases in defense-related enzyme activities and biochemicals, suggesting an induced resistance mechanism. The study found a 45% increase in peroxidase (POD) activity, a 50% increase in catalase (CAT) activity, a 30% increase in phenolic content, and a 25% increase in soluble protein content in the wheat plants treated with microbial antagonists. The study highlights the effectiveness of microbial antagonists, particularly B. subtilis strain DTBS-5, in managing wheat PM through biocontrol, induced resistance, and enhanced plant growth, offering a sustainable alternative to chemical treatments.

Epiphitic Microbiome of Alvarinho Wine Grapes from Different Geographic Regions in Portugal

Geographic location and, particularly, soil and climate exert influence on the typicality of a wine from a specific region, which is often justified by the terroir, and these factors also influence the epiphytic flora associated with the surface of the grape berries. In the present study, the microbiome associated with the surface of berries obtained from ten vineyards of the Alvarinho variety located in different geographical locations in mainland Portugal was determined and analyzed. The removal of microbial flora from the surface of the berries was carried out by washing and sonication, after which the extraction and purification of the respective DNA was carried out. High-throughput short amplicon sequencing of the fungal ITS region and the bacterial 16S region was performed, allowing for the determination of the microbial consortium associated with Alvarinho wine grapes. Analysis of α-diversity demonstrated that parcels from the Monção and Melgaço sub-region present a significantly (p < 0.05) lower fungal diversity and species richness when compared to the plots analyzed from other regions/sub-regions. The ubiquitous presence of Metschnikowia spp., a yeast with enologic potential interest in all parcels from Monção and Melgaço, was also observed.

Opposite Sides of Pantoea agglomerans and Its Associated Commercial Outlook

Multifaceted microorganisms such as the bacterium Pantoea colonize a wide range of habitats and can exhibit both beneficial and harmful behaviors, which provide new insights into microbial ecology. In the agricultural context, several strains of Pantoea spp. can promote plant growth through direct or indirect mechanisms. Members of this genus contribute to plant growth mainly by increasing the supply of nitrogen, solubilizing ammonia and inorganic phosphate, and producing phytohormones (e.g., auxins). Several other studies have shown the potential of strains of Pantoea spp. to induce systemic resistance and protection against pests and pathogenic microorganisms in cultivated plants. Strains of the species Pantoea agglomerans deserve attention as a pest and phytopathogen control agent. Several of them also possess a biotechnological potential for therapeutic purposes (e.g., immunomodulators) and are implicated in human infections. Thus, the differentiation between the harmful and beneficial strains of P. agglomerans is mandatory to apply this bacterium safely as a biofertilizer or biocontroller. This review specifically evaluates the potential of the strain-associated features of P. agglomerans for bioprospecting and agricultural applications through its biological versatility as well as clarifying its potential animal and human health risks from a genomic point of view.

Optimization of industrial (3000 L) production of Bacillus subtilis CW-S and its novel application for minituber and industrial-grade potato cultivation

A commercial plant probiotic product was developed employing Bacillus subtilis CW-S in submerged fermentation. The effects of molasses and urea on cell growth were investigated with the goal of low-cost manufacturing. Plackett–Burman and Central-Composite Design (CCD) were utilized to optimize production parameters to maximize productivity. The stability of the formulated product and its efficacy in cultivating minituber in aeroponics and industrial-grade potatoes in the field were assessed. The results showed that the medium BS10 (molasses and urea) produced satisfactory cell density (7.19 × 10⁸ CFU/mL) as compared to the control (1.51 × 10⁷ CFU/mL) and BS1-BS9 (expensive) media (1.84 × 10⁷–1.37 × 10⁹ CFU/mL). According to validated CCD results, optimized parameters fitted well in pilot (300 L; 2.05 × 10⁹ CFU/mL) and industrial (3000 L; 2.01 × 10⁹ CFU/mL) bioreactors, resulting in a two-fold increase in cell concentration over laboratory (9.84 × 10⁸ CFU/mL) bioreactors. In aeroponics, CW-S produced excellent results, with a significant increase in the quantity and weight of minitubers and the survival rate of transplanted plantlets. In a field test, the yield of industrial-grade (> 55 mm) potatoes was increased with a reduction in fertilizer dose. Overall, the findings suggest that CW-S can be produced commercially utilizing the newly developed media and optimized conditions, making plant probiotics more cost-effective and accessible to farmers for crop cultivation, particularly in aeroponic minituber and industrial-grade potato production.

Insight into a Successful Development of Biocontrol Agents: Production, Formulation, Packaging, and Shelf Life as Key Aspects

Biocontrol agents (BCAs) have been proposed and studied over recent decades as a suitable alternative to diminish or substitute synthetic fungicides used to control pre- and postharvest diseases. However, the development of BCAs has many constraints and obstacles that would have to be overcome before they could be successfully implemented in the market. For the BCA commercial development, the microorganism should be mass-produced on a large-scale, and, independently of the method used for the production, a particular plan regarding the formulation of BCAs by multidisciplinary approaches (liquid or solid) is required to optimize the yield, efficacy, and shelf life of the developed product. Unfortunately, not all BCAs can survive the conditions imposed during the formulation process. Improved stability can be achieved by either using special conditions during growing or by adding protective substances to the formulation medium. Finally, BCAs should be formulated in such a way as to guarantee long-term stability and ease of application of the product. Therefore, an accurate range of the packaging conditions should be considered to extend the shelf life of the formulated product, preferably up to two years. Herein, we discussed the main aspects regarding the production, formulation, packaging, and shelf life of BCAs.

Optimization of a food industry-waste-based medium for the production of the plant growth promoting microorganism Pseudomonas oryzihabitans PGP01 based on agro-food industries by-products

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Several agro-food industry wastes based on potato peels and pulp (FPP), tomato seeds (TS) and cereals (WB) industries were tested for their feasibility in producing P. oryzihabitans PGP01.

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The production of P. oryzihabitans PGP01 in a medium based on FPP supplemented with 10 g L⁻¹ of tryptone, 10 g L⁻¹ of sugar cane molasses, 5 g L⁻¹ nacl and 2.5 g L⁻¹ of K₂HPO₄ allowed to reach similar growth than the commercial medium.

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In 2 L bioreactors, a maximum of 4.4 × 10⁹ CFU mL⁻¹ of P. oryzihabitans PGP01 was obtained after 24 h of growth in the optimized medium, similar than laboratory medium.

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P. oryzihabitans PGP01 grown on the optimized medium preserved its biological activity, maintaining the same effect on roots of in vitro cultured plantlets than when it was grown in the commercial medium.

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This study shows how to re-use food-industry wastes for microbial production, reducing the amount of generated wastes.

In this study, three wastes based on potato peels and pulps, tomato seeds and wheat bran were used as basis for the preparation of a cheap medium to produce the bacterium P. oryzihabitans PGP01. In flasks experiments, P. oryzihabitans PGP01 growth at 25 °C in a medium based on frozen potato peels and pulp (FPP) with tryptone as a nitrogen source resulted in the maximum production compared to the commercial TSB medium. In the scale-up to 2 L bioreactors, FPP supplemented with tryptone, molasses, NaCl and K₂HPO₄ allowed to reach similar biomass production than in the TSB medium. A maximum growth of 4.4 × 10⁹ CFU mL⁻¹ after setting the agitation and the air flux conditions at 400 rpm and 0.75 vvm. Finally, P. oryzihabitans PGP01 growing in this optimized medium conserved its biological activity showing the expected effect in root development previously reported for this microorganism.

Microbial inoculation of seed for improved crop performance: issues and opportunities

There is increasing interest in the use of beneficial microorganisms as alternatives to chemical pesticides and synthetic fertilisers in agricultural production. Application of beneficial microorganisms to seeds is an efficient mechanism for placement of microbial inocula into soil where they will be well positioned to colonise seedling roots and protect against soil-borne diseases and pests. However, despite the long history of inoculation of legume seeds with Rhizobia spp. and clear laboratory demonstration of the ability of a wide range of other beneficial microorganisms to improve crop performance, there are still very few commercially available microbial seed inoculants. Seed inoculation techniques used for research purposes are often not feasible at a commercial scale and there are significant technical challenges in maintaining viable microbial inocula on seed throughout commercial seed treatment processes and storage. Further research is needed before the benefits of a wide range of environmentally sensitive potential seed inoculants can be captured for use in agriculture, ecosystem restoration and bioremediation. There is no single solution to the challenge of improving the ability of seed inoculants to establish and function consistently in the field. Development of novel formulations that maintain the viability of both inoculant and seed during storage will result from multidisciplinary research in microbial and seed physiology and adjuvant chemistry.

Bacillus velezensis RC 218 as a biocontrol agent to reduce Fusarium head blight and deoxynivalenol accumulation: Genome sequencing and secondary metabolite cluster profiles

Bacillus subtilis RC 218 was originally isolated from wheat anthers as a potential antagonist of Fusarium graminearum, the causal agent of Fusarium head blight (FHB). It was demonstrated to have antagonist activity against the plant pathogen under in vitro and greenhouse assays. The current study extends characterizing B. subtilis RC 218 with a field study and genome sequencing. The field study demonstrated that B. subtilis RC 218 could reduce disease severity and the associated mycotoxin (deoxynivalenol) accumulation, under field conditions. The genome sequencing allowed us to accurately determine the taxonomy of the strain using a phylogenomic approach, which places it in the Bacillus velezensis clade. In addition, the draft genome allowed us to use bioinformatics to mine the genome for potential metabolites. The genome mining allowed us to identify 9 active secondary metabolites conserved by all B. velezensis strains and one additional secondary metabolite, the lantibiotic ericin, which is unique to this strain. This study represents the first confirmed production of ericin by a B. velezensis strain. The genome also allowed us to do a comparative genomics with its closest relatives and compare the secondary metabolite production of the publically available B. velezensis genomes. The results showed that the diversity in secondary metabolites of strains in the B. velezensis clade is driven by strains making different antibacterials.

Detection and quantification by PCR assay of the biocontrol agent Pantoea agglomerans CPA-2 on apples

The registration of biological control agents requires the development of monitoring systems to detect and quantify the agent in the environment. Pantoea agglomerans CPA-2 is an effective biocontrol agent for postharvest diseases of citrus and pome fruits. The monitoring of CPA-2 in postharvest semi-commercial trials was evaluated by Rodac impression plates and the colonies isolated were confirmed by conventional PCR using the SCAR primers PAGA1 and PAGB1. Samples were taken from different surfaces that had contact with CPA-2, the surrounding environment and working clothes worn by handlers. Moreover, population dynamics of the strain CPA-2 were determined on apple surfaces using both the classical plating technique and real-time quantitative PCR (qPCR). A qPCR assay using a 3'-minor groove-binding (MGB) probe was developed for the specific detection and quantification of P. agglomerans strain CPA-2. Based on the nucleotide sequence of a SCAR fragment of CPA-2, one primer set and TaqMan MGB probe were designed. The primers SP2-F/SP2-R and the TaqMan MGB probe showed a specific detection of strain CPA-2 on apple surfaces, which was verified tested against purified DNA from 17 strains of P. agglomerans, 4 related Pantoea species, and 21 bacterial strains from other genera isolated from whole and also freshly-cut fruit and vegetables. The detection level was approximately 10(3) cells per reaction, and the standard curve was linear within a range of 5log units. Results from semi-commercial trials showed that CPA-2 had a low impact. The maximum persistence of P. agglomerans CPA-2 was not longer than 5days in plastic boxes stored at 0°C. Significant differences in CPA-2 population level dynamics were observed in results obtained by qPCR and dilution plating. These differences may indicate the presence of non-degraded DNA from non-viable cells. In conclusion, qPCR is a novel potential tool to quickly and specifically monitor recent surface colonisation by CPA-2 populations on apple surfaces during large-scale experiments that could ensure efficient and successful treatments.

Efficient synthesis of hydroxystyrenes via biocatalytic decarboxylation/deacetylation of substituted cinnamic acids by newly isolated Pantoea agglomerans strains

BACKGROUND

Decarboxylation of substituted cinnamic acids is a predominantly followed pathway for obtaining hydroxystyrenes-one of the most extensively explored bioactive compounds in the food and flavor industry (e.g. FEMA GRAS approved 4-vinylguaiacol). For this, mild and green strategies providing good yields with high product selectivity are needed.

RESULTS

Two newly isolated bacterial strains, i.e. Pantoea agglomerans KJLPB4 and P. agglomerans KJPB2, are reported for mild and effective decarboxylation of substituted cinnamic acids into corresponding hydroxystyrenes. Key operational parameters for the process, such as incubation temperature, incubation time, substrate concentration and effect of co-solvent, were optimized using ferulic acid as a model substrate. With strain KJLPB4, 1.51 g L⁻¹ 4-vinyl guaiacol (98% yield) was selectively obtained from 2 g L⁻¹ ferulic acid at 28 °C after 48 h incubation. However, KJPB2 provided vanillic acid in 85% yield after 72 h following the oxidative decarboxylation pathway. In addition, KJLPB4 was effectively exploited for the deacetylation of acetylated α-phenylcinnamic acids, providing corresponding compounds in 65-95% yields.

CONCLUSION

Two newly isolated microbial strains are reported for the mild and selective decarboxylation of substituted cinnamic acids into hydroxystyrenes. Preparative-scale synthesis of vinyl guaiacol and utilization of renewable feedstock (ferulic acid extracted from maize bran) have been demonstrated to enhance the practical utility of the process.

Selection of Biocontrol Agents of Pink Rot Based on Efficacy and Growth Kinetics Index Rankings

The microbiota of 84 different agricultural soils were transferred to separate samples of a γ irradiation-sterilized field soil enriched with potato periderm, and the resulting soils were assayed for biological suppressiveness to Phytophthora erythroseptica and their effect on zoospore production. The 13 most suppressive soil samples, which reduced zoospore production by 14 to 93% and disease severity on tubers by 6 to 21%, were used to isolate 279 organisms. Fourteen strains that reduce pink rot infections in preliminary tests were selected for further study. Six bacterial strains that reduced the severity of disease (P ≤ 0.05, Fischer's protected least significant difference) in subsequent tests were identified as Bacillus simplex (three strains), Pantoea agglomerans, Pseudomonas koreensis, and P. lini. Relative performance indices (RPIs) for biocontrol efficacy and for each of four kinetic parameters, including total colony-forming units (CFU_max), biomass production values (DW_max), cell production after 8 h (OD₈), and time of recovery from oxygen depletion (DT) were calculated for each strain. Overall RPI_Eff,Kin values for each strain then were calculated using strain RPI values for both efficacy (RPI_Eff) and kinetics (RPI_Kin). Strains with the highest RPI_Eff,Kin possess the best biocontrol efficacy of the strains tested and liquid culture growth characteristics that suggest commercial development potential.

Electrospun biohybrid materials for plant biocontrol containing chitosan and Trichoderma viride spores

Nanofibrous mats containing chitosan and Trichoderma viride spores were successfully prepared by electrospinning. The presence of the fungal spores in the nanofibrous mats was determined by scanning electron microscopy. The viability of the incorporated spores was estimated by cultivating the obtained biohybrids and studying the fungus growth. The fungal spores incorporated into the chitosan-containing fibrous mats were viable; the T. viride developed and reproduced normally. The electrospun biohybrid materials inhibited the growth of diverse phytopathogenic strains ( Fusarium, Alternaria) when placed at suitable growth conditions. Coating the plant sprouts with the biohybrids by direct electrospinning was easily done.

Effect of culture media and pH on the biomass production and biocontrol efficacy of aMetschnikowia pulcherrimastrain to be used as a biofungicide for postharvest disease control

Few strains of Metschnikowia pulcherrima (Pitt) M.W. Miller are under development for control of postharvest pathogens on fruit. A substrate was developed to optimize the biomass production of M. pulcherrima strain BIO126. Different complex nutrient sources, with or without pH control, were tested. Growth in yeast extract provided at concentrations ≥30 g·L–1yielded the highest biomass. The addition of two carbon sources, d-mannitol and l-sorbose, at 5 g·L–1each, significantly improved yeast growth. The greatest amount of yeast growth occurred when pH values of the medium ranged from 5.0 to 7.5. A combination of yeast extract, d-mannitol, and l-sorbose (YEMS), probably with diauxic utilization, showed a synergistic effect, widening the exponential phase (maximum specific growth rate of 0.45 h–1) and increasing the final cell number (1.5 × 109cells·mL–1) and dry biomass (6.0 g·L–1) in well-controlled batch fermentation. In efficacy trials on ‘Golden Delicious’ apples, M. pulcherrima grown in YEMS effectively reduced incidence and severity of Botrytis cinerea (51.1% and 70.8%, respectively) and Penicillium expansum (41.7% and 14.0%, respectively). Also on ‘Gala’ apples, the best reduction of grey and blue mould incidence was obtained with cells grown in YEMS (58.1% and 50.5%, respectively).

Utilization of winery wastes for Trichoderma viride biocontrol agent production by solid state fermentation

Biocontrol agents are safe and environmental friendly alternatives for pesticides in agriculture application. Trichoderma viride WEBL0703 performed a high level of antagonistic activity toward a broad spectrum of phytopathogens and was determined as a biocontrol agent, which was produced by solid state fermentation using grape marc and wine lees. The maximum yield of T. viride conidia was up to 6.65 x 10(9) CFU/g initial dry substrate (IDS) after 10 d fermentation. As important enzymes for protecting plants from disease, chitinase, beta-glucanase, and pectinase yields were 47.8 U/g IDS, 8.32 U/g IDS and 9.83 U/g IDS, respectively. These results show that it is feasible to convert winery wastes to a value-added and environmental friendly biocontrol agent.

Relative importance of amino acids, glycine-betaine and ectoine synthesis in the biocontrol agent Pantoea agglomerans CPA-2 in response to osmotic, acidic and heat stress

AIMS

The objective of this work was to determine the role of different compatible solutes in adaptation of Pantoea agglomerans CPA-2 at different stages of growth to solute (0.98, 0.97, 0.96 aw), heat (35 and 40 degrees C) and acidic (pH 4.0, 5.0, 6.0) stress.

METHODS AND RESULTS

Solute stress was imposed by using NaCl, glucose or glycerol, and pH was imposed with malic and citric acids. The accumulation of glycine-betaine, ectoine and amino acids in bacterial cells was quantified using high performance liquid chromathography (HPLC). There was a significant (P<0.05) accumulation of glycine-betaine (NaCl modified, 100-150 micromol g(-1) dry weight of cells) and ectoine (glucose modified media, >340 micromol g(-1) dry weight of cells) in the cells over a 48 h incubation period when compared with controls (<10 micromol g(-1) dry weight of cells). Chromatographic profile of amino acids was different with respect to control when NaCl or glucose was used as osmolyte.

CONCLUSIONS

Pantoea agglomerans CPA-2 cells synthesised significant amounts of glycine-betaine and ectoine in response to imposed solute stress. However, these compounds and tested amino acids were not involved in cellular adaptation to either heat or pH stress.

SIGNIFICANCE AND IMPACT OF THE STUDY

This type of information can be effectively applied to improve ecophysiological quality of cells of bacterial biocontrol agents for better survival and biocontrol efficacy in the phyllosphere of plants.

Acid tolerance response induced in the biocontrol agent Pantoea agglomerans CPA-2 and effect on its survival ability in acidic environments

The aim of this work was to optimize acid stress conditions for induction of acid tolerance response (ATR) in the biocontrol agent Pantoea agglomerans and study the effect of ATR induced on the ability to survive under acidic conditions. Initially, Pantoea agglomerans was grown in mild acidic conditions (pH 6.0, 5.5, 5.0 and 4.0) in order to induce ATR. The highest ATR was induced at initial pH of 5 using malic or citric acid. A first in vitro experiment was carried out. Thus, basal liquid medium at different pHs (3.0, 3.5, 4.0 and non-acidified) were then inoculated with acid-adapted and non-adapted inocula of P. agglomerans and survivals were examined during incubation at 25 or 4 degrees C. It was found that acid adaptation enhanced the survivals of Pantoea agglomerans CPA-2 cells at pH levels at which the cells were unable to grow (<3.5 and 4.0, at 25 and 4 degrees C, respectively). In contrast, in pH levels at which the cells were able to grow (pH 4.0 at 25 degrees C and non-acidified medium at 25 and 4 degrees C) no-differences were found between adapted and non-adapted cells. In in vivo tests, adapted and non-adapted cells were inoculated in wounds on mandarins and pome fruits. No differences were found between adapted and non-adapted cells and biocontrol efficacy was maintained. The present study demonstrated that exposure of Pantoea agglomerans to mild acidic conditions could induce acid resistance in this biocontrol agent.

Improving low water activity and desiccation tolerance of the biocontrol agent Pantoea agglomerans CPA-2 by osmotic treatments

AIMS

To study the improvement of tolerance to low water activity (aw) and desiccation during spray drying in Pantoea agglomerans cells subjected to mild osmotic stress during growth.

METHODS AND RESULTS

The micro-organism was cultured in an unmodified liquid (control) or in aw-modified media, and viability of these cells was evaluated on unstressed (0.995) and 0.96 aw stressed solid media, in order to check total viability and aw stress tolerance respectively. Significant improvements in viability on unmodified medium were observed with cells grown for 24 h in NaCl 0.98 aw, glycerol 0.98 aw and 0.97 aw and for 48 h in NaCl 0.98 aw and 0.97 aw modified media. Both yield improvements and water stress tolerance were achieved with low aw media. Cells grown for 24 h in NaCl 0.98 aw or for 48 h in NaCl 0.98 aw, 0.97 aw and 0.96 aw, glucose 0.97 aw and glycerol 0.97 aw showed improved aw stress tolerance in comparison with control cells. The best results were obtained with NaCl treatments (0.98 aw and 0.97 aw) which also exhibited better survival rates than control cells during spray-drying process and maintained their efficacy against postharvest fungal pathogens in apples and oranges.

CONCLUSIONS

NaCl treatments are very appropriate for improving P. agglomerans low aw tolerance obtaining high production levels and maintaining biocontrol efficacy.

SIGNIFICANCE AND IMPACT OF THE STUDY

Improving stress tolerance of biocontrol agents could be an efficient way to obtain consistency and maintain efficacy of biological control under practical conditions.

Accumulation of the compatible solutes, glycine-betaine and ectoine, in osmotic stress adaptation and heat shock cross-protection in the biocontrol agent Pantoea agglomerans CPA-2

AIMS

The effect of modifying the water activity (a(w)) of Pantoea agglomerans growth medium with the ionic solute NaCl on water stress resistance, heat-shock survival and intracellular accumulation of the compatible solutes glycine-betaine and ectoine were determined.

METHODS AND RESULTS

The bacterium was cultured in an unmodified liquid medium or that modified with NaCl to 0.98 and 0.97 a(w), and viability of cells evaluated on a 0.96 a(w)-modified solid media to check water stress tolerance. Cells grown under ionic stress had better water stress tolerance than control cells. These cells also had cross-protection to heat stress (30 min, 45 degrees C). The modified cells accumulated substantial amounts of the compatible solutes glycine-betaine and ectoine in contrast to the control cells, which contained little or none of these two compounds.

CONCLUSIONS

Improvement in osmotic and thermal tolerance of cells of the biocontrol agent P. agglomerans by modifying growth media with the ionic solute NaCl was achieved. The compatible solutes glycine-betaine and ectoine play a critical role in environmental stress tolerance improvement.

SIGNIFICANCE AND IMPACT OF THE STUDY

This approach provides a method for improving the physiological quality of inocula and could have implications for formulation and shelf-life of biocontrol agents.

State of the art and future prospects of the biological control of postharvest fruit diseases

Synthetic fungicides are the primary means to control postharvest diseases of fruits. Biological control has emerged as one of the most promising alternatives to chemicals. During the last 20 years, several biological control agents have been widely investigated for use on different pathogens and fruit crops. Many biological control mechanisms have been suggested for use on fruit including antibiosis, parasitism, induced resistance in the host tissue and competition. With the aim of extending the use of the biofungicides, there have been many studies on the application of various combinations of control agents, and on the application integrated with chemical and physical means of protection. The formulation and application methods are key issues for the efficacy and successful outcome of the commercial product. Genetic engineering may provide a useful tool in the enhancement of the biological control efficacy. Since biofungicides are usually not as effective as pesticides, this approach should be viewed as an important component of an integrated disease management scheme given that a significant and permanent reduction of pesticide use is our goal.

Optimization of growth conditions of the postharvest biocontrol agent Candida sake CPA-1 in a lab-scale fermenter

AIM

To maximize the growth (expressed as number of viable cells per millilitre) of the postharvest biocontrol agent Candida sake CPA(-1) at laboratory scale conditions.

METHODS AND RESULTS

Growth conditons (aeration, agitation speed and inoculum size) were studied in batch conditions in a 5 l fermenter using molasses and urea as growth medium. Consumption of sugars and urea were analysed. Fed-batch studies were also carried out. Glucose and fructose were consumed during the exponential growth phase and were depleted after 18 h of growth. On the contrary, C. sake cells assimilated sucrose during the stationary phase. There was not growth improvement when fed-batch technology was used. Addition of an extra amount of glucose or molasses after 18 h of growth did not contribute to increase final population.

CONCLUSIONS

Maximum growth (about 8 x 10(8 )CFU ml(-1)) was obtained at batch fermentation after 30 h growth at 400 rev min(-1), 150 l h(-1) of air and initial concentration of 106 CFU ml(-1).

SIGNIFICANCE AND IMPACT OF THE STUDY

The results obtained in this study are an approach for further upscaling of C. sake production.

The effect of nitrogen and carbon sources on growth of the biocontrol agent Pantoea agglomerans strain CPA-2

AIM

The effect of several nitrogen and carbon sources on the growth of Pantoea agglomerans (strain CPA-2) was studied for the first time.

METHODS AND RESULTS

Synthetic nitrogen and carbon sources were tested to obtain a suitable medium. Synthetic yeast extract provided maximum growth and disaccharides such as sucrose, lactose and trehalose improved this growth significantly from 3.2 x 10(9) to 5.5 x 10(9) cfu ml-1.

CONCLUSION

Pantoea agglomerans can be produced in a combination of nitrogen sources such as yeast extract with carbohydrates such as sucrose in shake flask and a laboratory fermenter (5 l).

SIGNIFICANCE AND IMPACT OF THE STUDY

Results suggest good production of this biocontrol agent on a laboratory scale and the potential of scaling up the process.

Water activity, temperature, and pH effects on growth of the biocontrol agent Pantoea agglomerans CPA-2

The growth response of the biocontrol agent Pantoea agglomerans to changes in water activity (a(w)), temperature, and pH was determined in vitro in nutrient yeast extract-sucrose medium. The minimum temperature at which P. agglomerans was able to grow was 267-272 kelvins (-6 to -1 degrees C), and growth of P. agglomerans did not change at varying pH levels (4.5-8.6). The minimum a(w) for growth was 0.96 in media modified with glycerol and 0.95 in media modified with NaCl or glucose. Solute used to reduce water activity had a great influence on bacterial growth, especially at unfavourable conditions (e.g., low pH or temperature). NaCl stimulated bacterial growth under optimum temperatures but inhibited it under unfavourable pH conditions (4.5 or 8.6). In contrast, the presence of glucose in the medium allowed P. agglomerans to grow over a broad range of temperature (3-42 degrees C) or pH (5-8.6) regimes. This study has defined the range of environmental conditions (a(w), pH, and temperature) over which the bacteria may be developed for biological control of postharvest diseases.

Effect of package and storage conditions on viability and efficacy of the freeze-dried biocontrol agent Pantoea agglomerans strain CPA-2

AIMS

To reduce concentrations of protective and rehydrating media and to evaluate the effect of storage temperature, packaging and atmosphere conditions on the stability of freeze-dried Pantoea agglomerans cells. Efficacy against Penicillium digitatum of freeze-dried cells in orange fruits was also evaluated.

METHODS AND RESULTS

Several concentrations of protective and rehydration media were tested to reduce processing costs. Freeze-dried cells were packed in glass vials or plastic bags under vacuum or nitrogen conditions at 4 and 25 degrees C. After 1 and 3 months, efficacy of freeze-dried P. agglomerans against P. digitatum was tested.

CONCLUSIONS

The results indicate that it is possible to reduce the concentration of non-fat skimmed milk as a rehydration medium from 10% to 1%, maintaining viabilities of 100%. Moreover, freeze-dried cells could be stored in glass vials or in high barrier plastic bags at 4 degrees C for 3 months while maintaining high viabilities and efficacy against P. digitatum.

SIGNIFICANCE AND IMPACT OF THE STUDY

The major obstacle in the commercialization of biocontrol products is the development of a shelf-stable formulated product that retains biocontrol activity at a level similar to that of fresh cells. This study suggests that it is possible to maintain viability and efficacy of freeze-dried P. agglomerans cells for at least 3 months.