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The objective of this study was to evaluate levels of sucrose on microbial growth. Roll tubes were filled with 15.6 mL of buffer Chen, 1 mL of inocula (rumen fluid from fistulated steer at pasture), 1 mL of Trypticase or hydrolyzed casein (1 g L-1 as final concentration) and 2.4 mL of sucrose solutions (0.00 g L-1, 0.37 g L-1, 0.75 g L-1, 1.5 g L-1, 3.0 g L-1, 6.0 g L-1, 12.0 g L-1, and 24.0 g L-1), in triplicate. The pH was 5.56 at 0 h and 4.6 after 6 h, and 5.83 in 0 g L-1 and 4.18 above 1.5 g L-1 of sucrose. The optical density (OD-600 nm) and microbial protein (MP-595 nm) tended to stabilize after 12 h and 6 g L-1 of sucrose, with no interaction between them. The OD (6 h to 24 h mean values) was curvilinear (hyperbolic), as a function of sucrose concentration, followed the saturation kinetics of Michaelis-Menten, which is typical of enzymes systems, and was described by the following Lineweaver-Burk equation: 1/OD = 0.508*(1/sucrose) + 1.15, R&sup2; = 0.99. The theoretical maximum microbial growth (1/a = kmax) was 0.87 OD and the concentration of sucrose to reach half of kmax (b/a = Ks) was 0.44 g L-1 of sucrose. The microbial growth was affected by incubation time, substrate concentration, and culture medium acidification. KEY-WORDS: Lineweaver-Burk; Michaelis-Menten; pH; saturation kinetics; sucrose. O objetivo deste estudo foi avaliar os n&iacute;veis de sacarose no crescimento microbiano. Tubos de ensaio foram preenchidos com 16,5 mL de tamp&atilde;o (meio Chen), 1 mL de in&oacute;culo (l&iacute;quido de r&uacute;men de bovino em pasto), 1 mL de Tripticase ou case&iacute;na hidrolisada (1 g L-1 como concentra&ccedil;&atilde;o final) e 2,4 mL de solu&ccedil;&atilde;o de sacarose (0,00 g L-1; 0,37 g L-1; 0,75 g L-1; 1,5 g L-1; 3,0 g L-1; 6,0 g L-1; 12,0 g L-1; e 24,0 g L-1), em triplicata. O pH foi de 5,56 &agrave; 0 hora (h) e 4,6 &agrave;s 6 h, 5,83 em 0 g L-1 e 4,18 acima de 1,5 g L-1 de sacarose. A densidade &oacute;ptica (DO-600 nm) e de prote&iacute;na microbiana (MP-595 nm) tenderam a se estabilizar ap&oacute;s 12 h e 6 g L-1 de sacarose, sem ocorr&ecirc;ncia de intera&ccedil;&atilde;o. A DO (valores m&eacute;dios entre 6 h e 24 h) foi curvil&iacute;nea (hip&eacute;rbole), em fun&ccedil;&atilde;o da concentra&ccedil;&atilde;o de sacarose, seguiu o modelo de satura&ccedil;&atilde;o cin&eacute;tica de Michaelis-Menten, t&iacute;pico do sistema enzim&aacute;tico, e foi descrita pela seguinte equa&ccedil;&atilde;o de Lineweaver-Burk: 1/DO = 0.508*(1/sacarose) + 1.15, R&sup2; = 0,99. O crescimento microbiano m&aacute;ximo te&oacute;rico (1/a = kmax) foi de 0,87 DO e a concentra&ccedil;&atilde;o de sacarose para atingir a metade kmax (b/a = Ks) foi de 0,44 g L-1 de sacarose. O crescimento microbiano foi afetado pelo tempo de incuba&ccedil;&atilde;o, concentra&ccedil;&atilde;o de substrato e acidifica&ccedil;&atilde;o do meio de cultura. PALAVRAS-CHAVE: Cin&eacute;tica de satura&ccedil;&atilde;o; Lineweaver-Burk; Michaelis-Menten; pH; sacarose.

CRESCIMENTO DE BACTÉRIAS RUMINAIS EM FUNÇÃO DA CONCENTRAÇÃO DE SUBSTRATO ENERGÉTICO EM MEIO DE CULTURA