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Pesquisa Agropecuária Tropical

On-line version ISSN 1983-4063

Abstract

OLIVEIRA, Tadeu Silva de et al. Growth rate of mixed ruminal bacteria as a function of energetic substrate concentration in bath culture. Pesqui. Agropecu. Trop. [online]. 2011, vol.41, n.1, pp.39-43. ISSN 1983-4063.  http://dx.doi.org/10.5216/pat.v41i1.6672.

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, R² = 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.

Keywords : Lineweaver-Burk; Michaelis-Menten; pH; saturation kinetics; sucrose.

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