The influence of different media and incubation temperatures on the quantification of microbial populations in sorghum, eucalyptus and forest soils was evaluated. Microbial growth was compared by using complex (tryptone soybean agar, TSA, casein-starch, CS, and Martin) and saline (Thorton, M3, Czapeck) media and incubation temperatures of 25 and 30 degrees C. Higher numbers of total bacterial and fungal colony-forming units (CFU) were observed in sorghum soils, and of spore-forming and Gram-negative bacteria in forest soils than other soils. Actinomycetes counts were highest in forest soil when using CS medium at 30 degrees C and in sorghum soil at 25 degrees C in M3 medium. Microorganism counts were dependent on the media and incubation temperatures. The counts at temperatures of 30 degrees C were significantly higher than at 25 degrees C. Microbial quantification was best when using TSA medium for total and spore-forming bacteria, Thorton for Gram-negative bacteria, M3 for actinomycetes, and Martin for fungi.

RESUMO: Este trabalho analisou o efeito da temperatura e período de incubação e da diluição do inóculo, em dois meios de cultura, sobre a quantificação de bactérias totais e esporuladas. O crescimento quantitativo e qualitativo de bactérias totais e esporuladas depende tanto do meio de cultura, temperatura, diluição e tempo utilizados como da interação desses fatores. O meio de TSA apresentou maior contagem que o meio de Thorton de unidades formadoras de colônias (UFC) de bactérias totais mas não de Bacillus spp. As colônias crescidas no meio de TSA apresentaram maior tamanho e forma mais nítida. O cultivo à temperatura de 30°C propiciou maior número de UFC que a 25°C, sobretudo nos primeiros dias de incubação. O crescimento bacteriano correspondeu a uma equação de 3 o grau. Dependendo do meio de cultura, da temperatura de incubação e da diluição, os períodos de máximo crescimento foram de 4,9 a 6,9 dias para as bactérias totais e de 4,4 a 7,2 dias para Bacillus spp. Embora tenham sido utilizadas diluições decimais dos inóculos, as proporções entre as contagens variaram de 6,3 a 10,0 vezes para as bactérias totais e de 2,0 a 7,0 para as esporuladas. Palavras-chave: Bacillus spp., bactérias totais, solo QUANTIFICATION OF TOTAL AND SPORULATING BACTERIA IN SOILSABSTRACT: This work studied the effect of the temperature and incubation time and of the inoculum dilution, in two culture media, on the quantification of total and sporulating bacteria. The quantitative and qualitative growth of total and sporulating bacteria depended on the growth medium, temperature, dilution and incubation time, as well as on the interaction of these factors. Tryptic Soil Agar medium presented a greater number of colony forming units (CFU) for total bacteria. However, for Bacillus spp. there were higher counts on Thorton medium. Colonies grown on Tryptic Soy Agar medium were of larger size and had a more clearly defined shape. An incubation temperature of 30 o C yielded more CFU than incubation at 25 o C, especially during the first days of incubation. Bacterial growth was fit to a mathematical model and corresponded to a third degree equation. Depending on the growth culture medium, incubation temperature and dilution, periods of maximum growth were between 4.9 and 6.9 days for total bacteria and between 4.4 and 7.2 days for Bacillus spp. Although decimal inoculum dilutions were used, proportions between counts based on different conditions ranged from 6.3 to 10.0 times for total bacteria and from 2.0 to 7.0 times for sporulating bacteria.

The number of colony forming units (CFU) of different groups of bacteria and fungi in samples stored at temperatures of 5 to -12oC 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 practically unchanged throughout the storage period. The number of Gram-negative bacteria decreased by as much as 69% 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 samples stored at 5oC. Except for the variations observed in fungal counts, the remaining groups of bacteria practically showed the same variation in number of colonies in soil samples stored at 5oC and -12oC.
Amostras de solo de um latossolo roxo foram armazenadas à temperatura de 5oC e -12oC, pelo período de 0-32 semanas, com o propósito de se avaliar a influência desses sistemas de conservação nas contagens de diferentes grupos de bactérias e fungos. O número de unidades formadoras de colônias (UFC) nos diferentes períodos de armazenagem foi comparado com o número de colônias obtido logo após a retirada das amostras do solo (tempo zero). O número de bactérias totais e de actinomicetos permaneceu praticamente invariável durante o período de armazenagem das amostras de solo. O número de bactérias Gram-negativas diminuiu em relação ao controle em até 69% enquanto o de Bacillus spp aumentou de 1,9 a 4,9 vezes, assim como o de fungos, a partir da 12a semana nas amostras armazenadas à temperatura de 5oC. Excetuando as variações observadas nas contagens de fungos, os demais grupos de bactérias mostraram, praticamente, a mesma tendência de variação no número de colônias nas amostras de solo armazenadas à temperatura de 5oC e -12oC

The enzymatic activity of soil samples stored at temperatures of 5 to -12oC 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.
Foi determinada a atividade enzimática de amostras de solo armazenadas às temperaturas de 5, -12oC e ambiente durante 0-32 semanas. A atividade da fosfatase alcalina e da desidrogenase diminuiu nas amostras armazenadas a baixas temperaturas, enquanto que a atividade da fosfatase ácida não variou em relação ao controle