Control of Acid Phosphatases Expression from Aspergillus niger by Soil Characteristics

ABSTRACTThis work studied the acid phosphatase (APase) activity from culture medium (extracellular, eAPase) and mycelial extract (intracellular, iAPase) ofAspergillus niger F111. The influence of fungus growth and phosphate concentration of the media on the synthesis and secretion of phosphatase was demonstrated. The effects of pH, substrate concentration and inorganic and organic compounds added to the reaction mixture on APase activity were also studied. Both enzymes were repressed by high concentrations of phosphate. Overexpression of iAPase in relation to eAPase was detected; iAPase activity was 46.1 times higher than eAPase. The maximal activity of eAPase was after 24h of fungus growth and for iAPase was after 96h. Optimal pH and substrate concentrations were 4.5 and 8.0 mM, respectively. Michaelis-Menten constant (Km) for the hydrolysis of p-nitrophenyl phosphate was 0.57 mM with Vmax = 14,285.71 U mg-1 mycelium for the iAPase and 0.31 mM with V max = 147.06 U mg-1 mycelium for eAPase. Organic substances had little effect on acid phosphatases when compared with the salts. Both the APases were inhibited by 10 mM KH 2PO4 and 5 mM (NH4)2MoO4; eAPase was also inhibited by 1 mM CoCl2.

Humic fractions of forest, pasture and maize crop soils resulting from microbial activity.

Humic substances result from the degradation of biopolymers of organic residues in the soil due to microbial activity. The objective of this study was to evaluate the influence of three different ecosystems: forest, pasture and maize crop on the formation of soil humic substances relating to their biological and chemical attributes. Microbial biomass carbon (MBC), microbial respiratory activity, nitrification potential, total organic carbon, soluble carbon, humic and fulvic acid fractions and the rate and degree of humification were determined. Organic carbon and soluble carbon contents decreased in the order: forest > pasture > maize; humic and fulvic acids decreased in the order forest > pasture = maize. The MBC and respiratory activity were not influenced by the ecosystems; however, the nitrification potential was higher in the forest than in other soils. The rate and degree of humification were higher in maize soil indicating greater humification of organic matter in this system. All attributes studied decreased significantly with increasing soil depth, with the exception of the rate and degree of humification. Significant and positive correlations were found between humic and fulvic acids contents with MBC, microbial respiration and nitrification potential, suggesting the microbial influence on the differential formation of humic substances of the different ecosystems.

Humic fractions of forest, pasture and maize crop soils resulting from microbial activity

Humic substances result from the degradation of biopolymers of organic residues in the soil due to microbial activity. The objective of this study was to evaluate the influence of three different ecosystems: forest, pasture and maize crop on the formation of soil humic substances relating to their biological and chemical attributes. Microbial biomass carbon (MBC), microbial respiratory activity, nitrification potential, total organic carbon, soluble carbon, humic and fulvic acid fractions and the rate and degree of humification were determined. Organic carbon and soluble carbon contents decreased in the order: forest > pasture > maize; humic and fulvic acids decreased in the order forest > pasture=maize. The MBC and respiratory activity were not influenced by the ecosystems; however, the nitrification potential was higher in the forest than in other soils. The rate and degree of humification were higher in maize soil indicating greater humification of organic matter in this system. All attributes studied decreased significantly with increasing soil depth, with the exception of the rate and degree of humification. Significant and positive correlations were found between humic and fulvic acids contents with MBC, microbial respiration and nitrification potential, suggesting the microbial influence on the differential formation of humic substances of the different ecosystems.

Enhanced solubilization of iron and calcium phosphates by Aspergillus niger by the addition of alcohols

The present study deals with the effect of increased concentrations of alcohols (methanol and ethanol) on the solubilization of FePO4 and CaHPO4 by Aspergillus niger. The efficiency of solubilization (ES) of inorganic phosphates, fungal growth, acid production and pH variation were determined. The concentrations of alcohols that most favored the solubilization of phosphates were 4% methanol and 3% ethanol. The ES of phosphates by the fungus in media containing methanol ranged from 11-96% and 0.4-87% for ethanol. The stimulation or inhibition of solubilization was dependent on greater or lesser fungus growth, acid production and decreased pH. These responses were supported by the correlation between the amount of phosphate dissolved and fungal growth (0.630** to 0.831**), the production of acids (0.529* to 0.989**) and a decrease in pH (-0.755** to -0.962**). Thus, the addition of alcohols facilitated insoluble phosphates dissolution during the fungus growth.

Synergistic action of both Aspergillus niger and Burkholderia cepacea in co-culture increases phosphate solubilization in growth medium.

Co-inoculation of the fungus Aspergillus niger and the bacterium Burkholderia cepacia was undertaken to understand the interaction between different species of phosphate-solubilizing microorganisms (PSM). PSM were inoculated in a single or mixed (A. niger-B. cepacia) culture. During 9 days of incubation, microbial biomass was enhanced, accompanied with increases in the levels of soluble phosphate and titratable acidity, as well as increased acid phosphatase activity. Production of acids and levels of phosphate solubilization were greater in the co-culture of A. niger-B. cepacia than in the single culture. The quantity of phosphate solubilized by the co-culture ranged from 40.51 ± 0.60 to 1103.64 ± 1.21 µg PO(4) 3- mL(-1) and was 9-22% higher than single cultures. pH of the medium dropped from 7.0 to 3.0 in the A. niger culture, 3.1 in the co-culture, and 4.2 in the B. cepacia culture. On the third day of postinoculation, acid production by the co-culture (mean 5.40 ± 0.31 mg NaOH mL(-1)) was 19-90% greater than single cultures. Glucose concentration decreased almost completely (97-99% of the starting concentration) by the ninth day of the incubation. These results show remarkable synergism by the co-culture in comparison with single cultures in the solubility of CaHPO(4) under in vitro conditions. This synergy between microorganisms can be used in poor available phosphate soils to enhance phosphate solubilization.

Growth and enzymatic responses of phytopathogenic fungi to glucose in culture media and soil

The effect of inoculation of Aspergillus flavus, Fusarium verticillioides, and Penicillium sp. in Dystrophic Red Latosol (DRL) and Eutroferric Red Latosol (ERL) soils with or without glucose on the total carbohydrate content and the dehydrogenase and amylase activities was studied. The fungal growth and spore production in culture medium with and without glucose were also evaluated. A completely randomized design with factorial arrangement was used. The addition of glucose in the culture medium increased the growth rate of A. flavus and Penicillium sp. but not of F. verticillioides. The number of spores increased 1.2 for F. verticillioides and 8.2 times for A. flavus in the medium with glucose, but was reduced 3.5 times for Penicillium sp. The total carbohydrates contents reduced significantly according to first and second degree equations. The consumption of total carbohydrates by A. flavus and Penicillium sp. was higher than the control or soil inoculated with F. verticillioides. The addition of glucose to soils benefited the use of carbohydrates, probably due to the stimulation of fungal growth. Dehydrogenase activity increased between 1.5 to 1.8 times (p <0.05) in soils with glucose and inoculated with the fungi (except F. verticillioides), in relation to soil without glucose. Amylase activity increased 1.3 to 1.5 times due to the addition of glucose in the soil. Increased amylase activity was observed in the DRL soil with glucose and inoculated with A. flavus and Penicillium sp. when compared to control.

Growth and enzymatic responses of phytopathogenic fungi to glucose in culture media and soil.

The effect of inoculation of Aspergillus flavus , Fusarium verticillioides , and Penicillium sp. in Dystrophic Red Latosol (DRL) and Eutroferric Red Latosol (ERL) soils with or without glucose on the total carbohydrate content and the dehydrogenase and amylase activities was studied. The fungal growth and spore production in culture medium with and without glucose were also evaluated. A completely randomized design with factorial arrangement was used. The addition of glucose in the culture medium increased the growth rate of A. flavus and Penicillium sp. but not of F. verticillioides . The number of spores increased 1.2 for F. verticillioides and 8.2 times for A. flavus in the medium with glucose, but was reduced 3.5 times for Penicillium sp. The total carbohydrates contents reduced significantly according to first and second degree equations. The consumption of total carbohydrates by A. flavus and Penicillium sp. was higher than the control or soil inoculated with F. verticillioides . The addition of glucose to soils benefited the use of carbohydrates, probably due to the stimulation of fungal growth. Dehydrogenase activity increased between 1.5 to 1.8 times ( p <0.05) in soils with glucose and inoculated with the fungi (except F. verticillioides ), in relation to soil without glucose. Amylase activity increased 1.3 to 1.5 times due to the addition of glucose in the soil. Increased amylase activity was observed in the DRL soil with glucose and inoculated with A. flavus and Penicillium sp. when compared to control.

Solubilization of CaHPO4 and AlPO4 by Aspergillus niger in culture media with different carbon and nitrogen sources

The solubilization of inorganic phosphates by microorganisms supplies phosphates for plant nutrition and increases their growth. The solubilization of CaHPO4 (Ca-P) and AlPO4 (Al-P) by Aspergillus niger using several carbon and nitrogen sources was studied. Solubilization of Ca-P was enhanced when the carbon sources were mannitol, maltose, galactose and glucose (in that order). Galactose, sucrose and maltose were the carbon sources that enhanced the solubilization of Al-P. More extensive growth, acid production, and decrease in pH were obtained in the Al-P medium than in the Ca-P medium, however, the quantity of solubilized phosphate was 12 percent less. Phosphate solubilization was related to acid production, pH drop and fungal growth in the culture medium. The results of a study carried out under abiotic conditions showed that organic acids solubilize more Ca-P than Al-P. Evaluating the effect of the nitrogen source, the solubilization of Ca-P or Al-P decreased in the following order: glycine > NH4Cl > NaNO3 and NH4NO3 > urea > (NH4)2SO4, respectively. Ammoniacal nitrogen (NH4+-N) sources were the most effective in the production of acids and in lowering of the pH.

A solubilização de fosfatos inorgânicos por microrganismos disponibiliza fosfato para a nutrição das plantas e aumenta seu crescimento. A solubilização de CaHPO4 (Ca-P) e AlPO4 (Al-P) por Aspergillus niger na presença de várias fontes de carbono e de nitrogênio foi estudada. A solubilização de Ca-P foi aumentada quando as fontes de carbono foram manitol, maltose, galactose e glicose (nesta ordem). Galactose, sacarose e maltose foram as fontes de carbono que aumentaram a solubilização de Al-P. Maior crescimento, produção de ácidos e diminuição do pH foram obtidos em meio contendo Al-P do que Ca-P, porém, a quantidade de fosfato solubilizado foi apenas 12 por cento maior. A solubilização dos fosfatos foi relacionada à produção de ácidos, diminuição do pH e crescimento do fungo no meio de cultura. Resultados de um estudo conduzido sob condições abióticas mostraram que os ácidos orgânicos solubilizaram mais Ca-P do que Al-P. Avaliando-se o efeito da fonte de N, a solubilização de Ca-P ou Al-P decresceu na seguinte ordem: glicina > NH4Cl > NaNO3 ou NH4NO3 > Uréia > (NH4)2SO4, respectivamente. As fontes de N amoniacal (NH4+-N) foram as mais efetivas na produção de ácidos e diminuição do pH.

Microrganismos produtores de hidrolases envolvidos nas transformações dos compostos do carbono e do nitrogênio do solo / Hydrolases producers microorganisms involved in the soil carbon and nitrogen cycling

Avaliou-se o efeito de culturas de braquiária e guandu, da adubaçäo fosfatada e da calagem sobre bactérias e fungos amilolíticos, celulolíticos, proteolíticos e ureolíticos. A proporçäo das bactérias com atividade enzimática em relaçäo ao total variou de 25 a 87 por cento e, a dos fungos, de 2 a 36 por cento. Os grupos de bactérias aumentaram sua populaçäo nas parcelas em que se aplicou superfosfato e calcário em relaçäo aos outros tratamentos (exceto as ureolíticas que aumentaram na ausência de adubo) e os fungos prevaleceram na ausência de adubaçäo (exceto os ureolíticos que aumentaram com superfosfato) e de calagem. No solo cultivado com braquiária, foram obtidas as maiores contagens de bactérias ureolíticas e fungos proteolíticos. Na ausência de planta, preponderaram os fungos CM-celulolíticos (CM, celulose microcristalina) e ureolíticos e na presença de guandu, os amilolíticos e CMC-celulolíticos (CMC, carboximetilcelulose). Os demais grupos de bactérias näo foram influenciados pelo sistema de cultivo. A populaçäo e a habilidade enzimática dos fungos foram menores que as das bactérias, o que sugere menor participaçäo na transformaçäo dos nutrientes no solo. As bactérias apresentaram múltiplas atividades enzimáticas, mostrando maior versatilidade que os fungos

Bacterial diversity in soil in response to different plants, phosphate fertilizers and liming

The diversity of bacterial isolates from soil in response to different plants (control, Brachiaria ruziziensis and Cajanus cajan), fertilization (control, simple superphosphate and rock phosphate) and liming (with and without lime) was evaluated. Phenotypic and physiological characteristics of the isolates were recorded and organized in a file to identify the bacteria. Among the isolates, 95 percent were Gram-positive and 5 percent Gram-negative rods. Soil cultivated with B. ruziziensis favored the nonsporing Gram-positive and Gram-negative rods compared to soil with C. cajan or uncultivated. Number of spore-forming Gram-positive rods were higher in plots with superphosphate than in unfertilized soil or soil fertilized with rock phosphate. In unfertilized plots, larger number of Gram-positive cocci and Gram-negative rods was obtained than in fertilized plots. Unlimed plots favored spore-forming Gram-positive rods, Gram-positive cocci and Gram-negative rods, while liming a larger proportion of nonsporing Gram-positive rods was found. From 7 to 86 percent of the total isolates utilized different carbohydrates. The recording data used in this experiment was effective in the isolates identification, and might be useful for diagnosis of soil bacteria. Bacillus, Cellulomonas, Rhodococcus, Enterobacter, Flavobacterium, Micrococcus and Arthrobacter were the genera more commonly found. Bacterial diversity was enhanced in limed, unfertilized and plant cultivated plots.

Germination and mycelial growth of Bipolaris euphorbiae Muchovej & Carvalho as influenced by herbicides and surfactants

Bipolaris euphorbiae Muchovej & Carvalho can be combined with herbicide in order to control a large spectrum of weed species, being a strong candidate for the biocontrol of Euphorbia heterophylla L. (milk weed). The fungus release can be combined with herbicide in order to control a broader spectrum of weed species. Thus. Laboratory experiments were set up to study the feasibility of using tank mixes of B. euphorbiae spores with herbicides or surfactants recommended for soybean. Mycelial growth and conidia germination were evaluated in PDA medium enriched with the herbicides oxasulfuron (80 g/ha), glyphosate (4 L/ha), bentazon (1.5 L/ha), fomesafen (1 L/ha), chlorimuron-ethyl (80 g/ha), lactofen (1 L/ha) and imazetaphyr (1 L/ha), and the surfactants Energic (2 ml/L), Aterbane (2.5 ml/L), Silwet L-77 Ag (1 ml/L), Herbitensil (2 ml/L) and Natur LÆóleo (10 ml/L). Dilution of the herbicides at 50 percent and 25 percent were evaluated based on solution consumption of 300 L/ha. The surfactants were evaluated only in the recommended concentrations. Mycelial growth was not affected by bentazon and fomesafen and slightly by oxasulfuron. However, glyphosate and the surfactants Energic, Herbitensil and Aterbane strongly reduced its growth. The reduction observed on imazetaphyr enriched medium was intermediate and the NaturÆóleo promoted mycelial growth. All of the surfactants allowed B. euphorbiae conidia germination equivalent to that reached in the presence of water. Energic and Herbitensil caused an expressive retardation on spore germination. The germinative process only began after 120 minutes in the presence of Herbitensil. In relation to the herbicides, it was observed that only in the presence of glyphosate and imazetaphyr the conidia germination did not follow the trend of the treatment with water.

Germination and mycelial growth of Bipolaris euphorbiae Muchovej & Carvalho as influenced by herbicides and surfactants

Bipolaris euphorbiae Muchovej & Carvalho can be combined with herbicide in order to control a large spectrum of weed species, being a strong candidate for the biocontrol of Euphorbia heterophylla L. (milk weed). The fungus release can be combined with herbicide in order to control a broader spectrum of weed species. Thus, laboratory experiments were set up to study the feasibility of using tank mixes of B. euphorbiae spores with herbicides or surfactants recommended for soybean. Mycelial growth and conidia germination were evaluated in PDA medium enriched with the herbicides oxasulfuron (80 g/ha), glyphosate (4 L/ha), bentazon (1.5 L/ha), fomesafen (1 L/ha), chlorimuron-ethyl (80 g/ha), lactofen (1 L/ha) and imazetaphyr (1 L/ha), and the surfactants Energic (2 ml/L), Aterbane (2.5 ml/L), Silwet L-77Ag (1 ml/L), Herbitensil (2 ml/L) and Natur L'óleo (10 ml/L). Dilution of the herbicides at 50% and 25% were evaluated based on solution consumption of 300 L/ha. The surfactants were evaluated only in the recommended concentrations. Mycelial growth was not affected by bentazon and fomesafen and slightly by oxasulfuron. However, glyphosate and the surfactants Energic, Herbitensil and Aterbane strongly reduced its growth. The reduction observed on imazetaphyr enriched medium was intermediate and the Natur L'óleo promoted mycelial growth. All of the surfactants allowed B. euphorbiae conidia germination equivalent to that reached in the presence of water. Energic and Herbitensil caused an expressive retardation on spore germination. The germinative process only began after 120 minutes in the presence of Herbitensil. In relation to the herbicides, it was observed that only in the presence of glyphosate and imazetaphyr the conidia germination did not follow the trend of the treatment with water.

Bipolaris euphorbiae Muchovej & Carvalho é um forte candidato para o controle de Euphorbia heterophylla L. (amendoim bravo). Este fungo pode ser aplicado em combinação com herbicidas para controlar um maior espectro de espécies daninhas. Para tanto, experimentos laboratoriais foram realizados para verificar a possibilidade da utilização de mistura de tanque de esporos de B. euphorbiae e herbicidas ou surfatantes recomendados para a cultura da soja. Crescimento micelial e germinação de conídios foram avaliados em meio BDA acrescido dos herbicidas, nas concentrações recomendadas dos produtos comerciais, oxasulfuron (80 g/ha), glifosato (4 L/ha), bentazon (1.5 L/ha), fomesafen (1 L/ha), chlorimuron-ethyl (80 g/ha), lactofen (1 L/ha) e imazetaphyr (1 L/ha) e dos surfatantes Energic (2 ml/L), Aterbane (2,5 ml/L), Silwet L-77Ag (1 ml/L), Herbitensil (2 ml/L) e Natur L'óleo (10 ml/L). Diluições dos herbicidas de 50% e 25% foram avaliadas com um consumo de calda equivalente a 300 L/ha. Os surfatantes foram somente utilizados nas concentrações recomendadas. O crescimento micelial não foi afetado por bentazon e fomesafen e apenas levemente por oxasulfuron. Porém, glifosato, chlorimuron-ethyl, lactofen, Energic, Herbitensil, Silwet, e Aterbane o reduziram drasticamente. A redução observada com imazetaphyr foi intermediária e Natur L' óleo promoveu o crescimento micelial. Na presença dos surfatantes, observou-se que todos permitiram uma porcentagem de germinação equivalente àquela alcançada na presença de água. Energic e Herbitensil causaram um retardamento expressivo. Com Herbitensil, o processo germinativo iniciou somente aos 120 minutos. Com herbicidas, foi observado que somente na presença de glifosato e imazetaphyr a germinação dos conídios não seguiu a tendência observada com água, como ocorreu com os outros produtos testados.

Control of amylase production and growth characteristics of Aspergillus ochraceus.

The growth and the extracellular amylase production by Aspergillus ochraceus were studied in a stationary culture medium. Maximum growth rate of this fungus was found after 5 days of incubation at 30 degrees C, but maximum amylase production was obtained after 2 days. The highest amylase production were attained with lactose, maltose, xylose and starch as carbon sources. The extracellular amylase production and mycelial growth were influenced by the concentration of starch. Other carbohydrates supported growth but did not induce amylase synthesis and glucose repressed it, indicating catabolite repression in this microorganism. The presence of both mechanisms of induction and repression suggests that at least these multiple forms of regulation are present in A. ochraceus. Of the nitrogen sources tested, casaminoacids, ammonium nitrate and sodium nitrate stimulated the highest yield of amylase. Optimal amylase production was obtained at pH 5.0, but enzyme activity was found only in the 4.0-6.0 pH range. These results were probably due to the inhibitory effect of NH4(+)-N in the culture medium.

Microbial counts of dark red latosol samples stored at different temperatures

The number of colony forming units (CFU) of different groups of bacteria and fungi in samples stored at temperatures of 5 to -12§C for 0-32 weeks was evaluated. The number of CFU obtained after the different periods of storage of red latossol soil was compared with the number of colonies obtained immediately after removal of soil samples (time zero). The number of total bacteria and actinomycetes in the samples remained pratically unchanged throughout the storage period. The number of Gram-negative bacteria decreased by as much as 69 per cent compared to control, while the number of Bacillus spp and of fungi increased 1.9 to 4.9 times starting from the 12th week in sample stored at 5§C. Except for the variations observed in fungal counts, the remaining groups of bacteria pratically showed the same variation in number of colonies in soil samples stored at 5§C and -12§.

Microbial activity of dark red latosol samples stored at different temperatures

The enzymatic activity of soil samples stored at temperature of 5 to 12§C and at room temperature for 0-32 weeks was determined. While alkaline phosphatase and dehydrogenase activity was decreased compared to control in samples stored at low temperatures, acid phosphatase activity showed no significant change.

Efeito da concentraçäo de fosfato na solubilizaçäo de fluorapatita por Aspergilllus niger / Effect of phosphate on the solubilization of fluorapatite by Aspergillus niger

A síntese da fostatase ácida em Aspergillus niger foi controlada pela concentraçäo de fosfato inorgânico do meio de cultura. A adiçäo de fluorapatita reprimiu a produçäo da enzima devido a solubilizaçäo do fosfato insolúvel pelo fungo. A produçäo da fosfatase e a solubilizaçäo da fluorapatita diminuiram com o aumento da concentraçäo saturante de fosfato. Quando A.niger, cultivado em emio pobre em fosfato, foi transferido para meio rico, verificou-se a repressäo da solubibilizaçäo. Por outro lado, a transferência de micélio de meio rico em fosfato para meio pobre contendo fluorapatita estimulou a solubilizaçäo. Näo foi possível relacionar a produçäo de ácidos totais ou a queda do pH, na presença ou ausência de fluorapatita e o processo de solubilizaçäo. Aparentemente, o processo de solubibilizaçäo é controlado pelos níveis de fosfato exógeno de modo similar as fosfatases

Sensibilidade do Aspergillus niger ao Thiram / Sensitivity of Aspergillus niger to thiram

O fungo Aspergillus niger foi cultivado em meios sólidos e líquido acrescidos de diferentes concentrações do fungicida thiram. Em meio sólido, contendo 60 µg/ml de thiram, o crescimento micelial foi inibido em 78 por cento em relação ao controle e, em meio líquido contendo 30 µg/ml, esta inibição foi de 89 por cento, após 4 dias de incubação. A produção de esporos sofreu redução de 89 por cento frente a 50 µg/ml do fungicida. Menor teor de proteína meineral foi observado quando se aumentou a concentração do thiram, indicando que o mecanismo de síntese de proteína foi alterado. Para um período de incubação de 7 dias, não ocorreu inibição do crescimento do fungo. Também não foi observado efeito inibidor quando o fungicida foi adicionado ao meio de cultura por períodos de 1 a 4 dias, anteriores à inoculação do fungo. É possível que após um período de incubação prolongado, o fungo tenha crescido às custas do fungicida sujeito a uma degradação prévia não enzimática.

Liberaçäo das fosfatases ácida e alcalina repressíveis de Neurospora grassa por detergentes e sais / Liberation of repressibles acid and alkaline phosphatases from Neurospora grassa by detergents and salts

O efeito de diversos compostos químicos sobre a liberaçäo das fosatases ácidas e alcalina repressíveis de Neurospora crassa foi estudado. A fosfatase ácida teve sua atividade estimulada quando adicionaram ao meio de cultura Twee 80, Tween 20 e dodecilsulfato de sódio (SDS) enquanto que a atividade da fosfatase alcalina foi favorecida por Twen 80, Tween 20, SDS, desoxicolato de sódio, NaCl e KCl. Além do efeito sobre a liberaçäo das enzimas, os detergentes näo iônicos, Tween 80, Tween 20 e Triton X-100, adicionados à mistura de reaçäo, estimularam a atividade da fosfatase ácida enquanto que os iônicos, taurocolato de sódio e SDS, a inibiram. Esse efeito näo foi observado com a fosfatase alcalina. Concentraçöes crescentes de Tween 80 aumentaram a secreçäo da fosfatase ácida e de proteína. A liberaçäo da fosfatase ácida foi dependente do tempo, culminando a atividade da enzima após 3 horas de adiçäo do Tween 80

Efeito de inóculo micorrizicos vesículo arbusculares provenientes de diferentes plantas doadoras sobre o milho / Effect of inocula of vesicular orbuscular Mycorrhiza obtained from distinct plantis on corn

conduziu-se em casa de vegataçäo, um ensaio onde o mesmo tempo em que se testou uma técnica de adiçäo de inóculos de fungos micorrízicos se comparou três plantas hospedeiras como doadoras dos mesmos. A técnica empregada consiste na adiçäo, localizada logo abaixo de linha em que ficaräo as sementes de uma cama de fragmentos de raízes micorrizadas, recém-coletadas. As fornecedoras destas inóculos foram: Paspalum notatum Flugge, Oryza sativa Lineu e Zea mays Lineu e a receptora Z. mays L. Ao final do experimento verificou-se que a técnica estudada propiciou bons resultados e que o P. notatum se mostrou mais promissor como fornecedor de fungo micorrízico, recomendando-se maior atençäo aomesmo. Ainda, pelo emprego de duas fontes de fósforo, pode-se concluir que efetivamente o inóculo de P. notatum aumenta a capacidade da planta em absorver o fósforo disponível, näo atuando como solubilizador de fosfato (au)

Caracterizaçäo da lipase secretada por Rhizopus oligosporus

A lipase secretada no meio de cultura por Rhizopus oligosporus apresenta maior velocidade de hidrólise nos tempos iniciais da reaçäo enzimática ou em concentraçöes menores de enzima. O efeito do pH da reaçäo enzimática sobre a atividade lipolítica propicia uma curva com maior velocidade de hidrólise em valor de pH 8,5 e nitidamente descendente do lado alcalino do pH da reaçäo. Sais minerais, como o cloreto de sódio e o cloreto de cálcio, adicionados à mistura de reaçäo, aumentam a atividade lipolítica em cerca de 45% em média. Por sua vez, os sais biliares (taurocolato e desoxicolato de sódio) ativam a enzima em 22-25% quando em concentraçöes baixas e inibem acentuadamente quando em concentraçöes altas. A enzima secretada no meio de cultura suplementado com extrato de farelo de soja, óleo de soja ou Tween 80 apresenta uma pequena atividade de esterase em níveis correspondentes à atividade de lipase