María Cristina Maldonado’s research while affiliated with National University of Tucumán and other places

Geotrichum citri-aurantii is a postharvest phytopathogenic fungus of lemons. We studied the mode of action of antifungal metabolites from Bacillus sp. strain IBA 33 on arthroconidia of G. citri-aurantii. These metabolites are lipopeptides belonging to the iturin family. Membrane permeabilization of G. citri-aurantii was analyzed and mitochondrial respiratory rate was evaluated. Disturbance of the plasma membrane promotes the leakage of many cellular components into the surrounding media, and mitochondrial membrane disorganization promotes the inhibition of the respiratory rate. Our findings provide insights into the ability of lipopeptides to suppress plant fungal pathogens and their possible agronomical applications.

The increments of plant diseases caused by the proliferation of fungicide-resistant pathogens intensified the research of new active metabolites against them. The study of biological methods as an alternative to chemical control has reach relevance in recent years. It has been suggested that the use of metabolites from Bacillus, is an alternative or supplementary method to chemical plant protection, if they are not toxic for the consumers and environmentally friendly. The toxicity of different concentrations of antifungal metabolites produced by Bacillus sp. IBA 33 was evaluated. Their ability to induce cytotoxic effects was investigated by different tests as hemolysis, and Artemia salina and Allium cepa L immobilization. With 2.56 mg/ml of antifungal metabolites hemolysis reached 24.07%, to 1.28 mg/ml was 14%. HC50 was 10.41 mg/ml. A. salina nauplii exposed to 3.2, 1.6 and 0.8 mg/ml of antifungal metabolites showed 80, 20 and 10% of mortality respectively; LD50 was 2.24 mg/ml. In Allium cepa L test after 72 h of treatment, the roots lengths were 8.75, 10.35 and 23.75 mm with 3.2, 1.6 and 0.8 mg/ml of antifungal metabolites respectively. The EC50 was 0.078 mg/ml. After 144 h the EC50 was 4.11 mg/ml. Only with 3.2 mg/ml of metabolites, chromosomal aberrations, cytoplasm vacuolization and decentralization of nuclei were observed in the cells of Allium cepa L. No micronuclei were detected. Under the experimental conditions, the antifungal metabolites concentrations assayed are considered non toxic. © 2015, Asociacion Espanola de Toxicologia. All rights reserved.

Alicyclobacillus acidoterrestris is considered to be one of the important target microorganisms in the quality control of acidic canned foods. There is an urgent need to develop a suitable method for inhibiting or controlling the germination and outgrowth of A.acidoterrestris in acidic drinks. The aim of this work was to evaluate the chemicals used in the lemon industry (sodium benzoate, potassium sorbate), and lemon essential oil as a natural compound, against a strain of A.acidoterrestris in MEB medium and in lemon juice concentrate. The results pointed out that sodium benzoate (500-1000-2000 ppm) and lemon essential oil (0.08-0.12-0.16%) completely inhibited the germination of A. acidoterrestris spores in MEB medium and LJC for 11 days. Potassium sorbate (600-1200 ppm) was more effective to inhibit the growth of the microbial target in lemon juice than in MEB medium. The effect of sodium benzoate, potassium sorbate and essential oil was sporostatic in MEB and LJC as they did not affect spore viability.

Lemon growing areas in the north of Argentina have industries that produce concentrated juice, peel and essential oil and generate a significant amount of liquid and solid waste as lemon pulp. In Argentina, despite the potential applications that the pulp has as animal feed and human and industrial raw material, only 10% is used for these purposes and the rest is discarded into the environment causing many ecological and economic problems. There is little information in the literature on biotechnologies for the treatment of this industrial waste. This paper shows that lemon pulp is a suitable substrate to be treated by anaerobic digestion. We obtained 86 and 92% reduction of chemical oxygen demand in a digester with a semi-continuous feed and retention time of 10 and 20 days respectively and a productivity of 0.406 g CH(4)/g VS h. Comparative tests showed that pre-digesting the pulp improved the process of digestion and increased biogas generation by 20%.

We studied a process employed for treating lemon industry effluents, using the macrophyte Eishhornia crassipes (water hyacinth) in a phytoremediation tank with a 6000-L workload. The diluted effluents BOD and COD were reduced to 70 and 61%, respectively, working with a 1.5-h hydraulic residence time (HRT). We investigated the effect of adding every 12 h an inoculum consisting of a consortium of microorganisms isolated from the macrophyte roots and recirculating 30% of the outflow. In this way, we achieved a volumetric removal rate (VRR) of BOD = 354 g/m3 day. Plants were daily harvested from the tank to maintain growth rate and the density originally planted. We studied their use for biogas production in an anaerobic digester working with 12 and 16 days of hydraulic residence time. The yield obtained was 0.87 L/g and productivity 0.87 L/L day with a loading rate of 5 g/L day. Integrating both processes on an industrial scale would solve the effluent pollution problem and generate an energy source that could be used by the industry itself to lower its production costs.

Streptomyces strains may control postharvest lemon fruit diseases caused by Penicillium digitatum and Geotrichum candidum. Four Streptomyces strains (RO3, MC3, Alem and CE1) were tested and RO3 was the strain with the highest antagonistic activity. Streptomyces RO3 showed a maximum biomass value (2.15 g/L) after 72 h incubation in yeast extract, malt extract, glucose (YMG) medium; in starch casein medium the highest value was 0.477 g/L at 120 h incubation. The metabolites produced in YMG medium showed the maximum inhibition against G. candidum and P. digitatum (19.64 and 62.12% respectively). The inhibitory activity of metabolites decreased after autoclaving. RO3 metabolites have molecular mass higher than 2000 and they have fungicidal action mode against P. digitatum. In vivo assays, RO3 metabolites with wax, totally controlled lemon diseases (mainly sour rot and green mold). This is the first study on Streptomyces to control postharvest lemon diseases.

A biological treatment was designed for lemon pulp waste, a residual product from the lemon processing industry that causes A biological treatment was designed for lemon pulp waste, a residual product from the lemon processing industry that causes many economic and environmental problems. The technique was carried out in two stages. In the first one, the pulp was treated many economic and environmental problems. The technique was carried out in two stages. In the first one, the pulp was treated with microorganisms until reaching partial digestion and increasing pH from 3.8 to neutrality. In the second, the predigested with microorganisms until reaching partial digestion and increasing pH from 3.8 to neutrality. In the second, the predigested pulp of the first stage was treated with earthworms of the Eisenia foetida variety for 90days, thus transforming the residue into humus and propagating the earthworms with an individual mean growth pulp of the first stage was treated with earthworms of the Eisenia foetida variety for 90days, thus transforming the residue into humus and propagating the earthworms with an individual mean growth of 2.34mg/day. The process is simple and transforms a highly contaminant solid residue into commercially valuable products of 2.34mg/day. The process is simple and transforms a highly contaminant solid residue into commercially valuable products like humus and earthworms. Different germination and phytotoxicity assays were performed with assorted seeds to establish like humus and earthworms. Different germination and phytotoxicity assays were performed with assorted seeds to establish humus properties. humus properties.

Bacillus sp strain IBA 33 metabolites, isolated from decaying lemon fruits, were evaluated for the control of pathogenic and non-pathogenic fungi ( Penicillium digitatum, Geotrichum candidum, Penicillium expansum, Aspergillus clavatus, Aspergillus flavus, Aspergillus niger, and Fusarium moniliforme). These metabolites were recovered from Landy medium (LM) without aminoacids. In order to optimize metabolites production the LM was modified by adding different concentrations and sources of amino acids and carbohydrates at different culture conditions. Bacillus sp strain IBA 33 metabolites efficacy to control fungi were evaluated with in vitro and in vivo assays. A. flavus growth inhibition was 52% with the metabolites of Bacillus sp strain IBA 33 recovered from LM (MBLM) in vitro assays. MBLM supplemented with 0.5% glutamic acid, inhibited the growth of P. digitatum, G. candidum, A. clavatus, A. niger and F. moniliforme by 65%, 88.44%, 84%, 34% and 92% respectively. The highest inhibition of P. expansum was 45% with MBLM supplemented with 0.5% aspartic acid. Similar results were obtained in vivo assays. These results showed that Bacillus sp strain IBA 33 metabolites specificity against fungi depended on the composition of the LM.

A pilot plant with a 10-m3 airlift reactor, a settler and a 300-m3 pond were developed for the treatment of the lemon processing industry wastewater. The aim of this work is to evaluate reactor and pilot plant performance. We worked in a continuous system with activated sludge, using wastewater microorganisms and testing the most important parameters of the process (HRT, SRT, F/M, VRC, K La). An outflow settler tube added to the reactor design increased sludge concentration in 25% at 200–500l/h flow rates. At 600–800l/h flow rates sludge concentration was 10–15% higher. Volumetric removal capacity of the suspended solid in the reactor was more than 6kg BOD5/m3day with lesser than 17h hydraulic retention time. Maximum BOD5 removal was 92% with 200l/h flow. The reactor had a good mixing performance and a satisfactory volumetric mass transfer coefficient. Efficient reactor design made foam disposal easy. The effluent came out of the pond with DBO=50mg/l, i.e. a total BOD removal of 99% with 600l/h flow. The pond also had a very important function: it completely eliminated reactor produced biomass by using a natural degradation process.

The increasing urban and industrial development has brought about numerous important problems that affect both ecosystems and human health. An alternative instrument for the determination of toxicity in environmental samples is the use of bioassays. In this work we studied the possibility of using lettuce, chicory and endive to evaluate the toxicity of different toxic compounds. Lettuce seeds showed a higher sensitivity to toxic substances than either chicory or endive seeds, these two being used for the first time in bioassays. We also evaluated the efficiency of the use of the above seeds in the determination of the toxicity of two industrial wastes, one from a citrus processing factory and the other from a sugar mo lasses alcohol distillery.