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Amylase production by Citrobacter sp. isolated from potato was optimized in batch culture studies under shake flask conditions. Effects and interactions of best sources and levels of carbon and nitrogen estimated by 4 x 5 and 4 x 4 factorial experimental arrangements were significant (P < 0.01) on amylase production. Optimal alpha-amylase yield was obtained in a medium containing sorghum flour (2.0 % w/v) and a mixture of (NH4)2SO4 + soybean meal (1.5% w/v) with an initial medium pH of 8.0. Under optimum conditions, amylase yield was maximal (0.499 U/ml) after 60h incubation at room temperature (28oC ± 2oC). Characterization studies showed that the enzyme had maximum activity at 60oC, retained 100% of its original activities at 60oC for 2h, was maximally active at pH 7.0 and retained 100% of original activities at pH 9.0 for 2h. Enzyme activity was stimulated by urea, Mg2+, Ca2+ and Zn2+ but inhibited by Hg2+.

The impacts of Hg2+, Cd2+ and Zn2+ on the activities of periplasmic nitrate reductase (NAP) and dehydrogenase (DHA) enzymes of three organisms isolated from soil and sediment-water interface were analysed in liquid culture studies. NAP and DHA activities were estimated from nitrite and triphenyl formazan were produced respectively after 4h incubation at 28 ± 2oC. Hg2+ completely inhibited NAP activity in Escherichia and Pseudomonas spp at all the concentrations (0.2 – 1mM) while progressive inhibitions of NAP activity were observed in Escherichia and Pseudomonas spp with increasing concentrations of Zn2+ and Cd2+. Both metals were stimulatory to NAP of Acinetobacter sp at 0.2 – 1mM. Apart from stimulation of DHA activity by Zn2+ (0.2 – 1mM) in Escherichia sp, Cd2+ (0.4 -1.0mM) in Acinetobacter sp and (1.0mM) in Pseudomonas sp, all the metals progressively inhibited DHA activities in the three organisms. In Escherichia sp, the activities of the two enzymes were negatively correlated on exposure to Zn2+ (r = -0.91) and positively correlated (r = >0.90) on exposure to Cd2+ and Hg2+. Based on IC50 values of the metals for the DHA and NAP enzymes, the most resistant of the three organisms were Escherichia sp and Acinetobacter sp respectively. Quantitatively, NAP with its lower IC50 values than DHA was a more sensitive toxicity measure for Hg2+ in all the organisms. The sensitivity of microbial metabolic enzymes to the toxic effects of metals varies with the type of enzyme, metal and the microorganism involved.

O artigo discute o momento educacional em que vivem os países latino-americanos, nos quais a cobertura do ensino fundamental tende a se universalizar, sem que tenham sido resolvidos os crônicos problemas de qualidade, expressos pelos altos índices de repetência e evasão. Contrapondo esse quadro educacional às novas demandas da modernização tecnológica e da participação social da população, as autoras propõem uma revisão do modelo de gestão da escola, voltado para a autonomia, baseado em projeto pedagógico próprio e avaliação dos resultados, bem como uma redefinição das fun��ões do Estado e das estruturas centralizadas dos sistemas de ensino.This article discuss the educational problems of Latin American countries wich has experienced a high degree of elementary school attendance, without reaching good standards of quality. The authors point out that the educational system should change to meet the demands imposed on it by the technological modernization and greater social participation of the population. They emphasize the need to change the way the public school is managed today, toward a less centralized educational system and a greater degree of autonomy of the schools, in a such way that each one could develop its own pedagogical plan and be submitted to evaluation of performance.