title: Signals of aging associated with lower growth rates in Kluyveromyces lactis cultures under nitrogen limitation.
abstract: The effects of aging on the specific growth rate of Kluyveromyces lactis cultures, as a function of (NH4)2SO4 concentration, were evaluated. The growth kinetic parameters maximum specific growth rate and saturation constant for (NH4)2SO4 were calculated to be 0.44 h(-1) and 0.15 mmol·L(-1), respectively. Batch cultures were allowed to age for 16 days without influence of cell density or starvation. The specific growth rates of these cultures were determined each day and decreased as the population aged at different nitrogen concentrations. Aging signals (N-acetylglucosamine content of the cell wall, cell dimensions, and apoptosis markers) were measured. Apoptosis markers were detected after 5 days at limiting (NH4)2SO4 concentrations (0.57, 3.80, and 7.60 mmol·L(-1)) but only after 8 days at a nonlimiting (NH4)2SO4 concentration (38.0 mmol·L(-1)). Similarly, continuous cultures of K. lactis performed under nitrogen limitation and, at lower dilution rates, accumulated cells exhibiting aging signals. The results demonstrate that aging affects growth rate and raise the question of whether nitrogen limitation accelerates aging. Because aging is correlated with growth rate, and each dilution rate of the continuous cultures tends to select and accumulate cells with a respective age, cultures growing at lower growth rates can be useful to investigate yeast physiological responses, including aging.
authors.affiliation: a Departamento de Microbiologia, Universidade Federal de Viçosa, Av. P.H. Rolfs s/n 36571-000, Laboratório de Fisiologia de Microrganismos, BIOAGRO, Viçosa - MG, Brasil.
authors.forename: Lygia Fátima da Mata
authors.initials: LF
authors.lastname: Corrêa
authors.forename: Frederico José Vieira
authors.initials: FJ
authors.lastname: Passos
authors.forename: Marlene Isabel Vargas
authors.initials: MI
authors.lastname: Viloria
authors.forename: Olindo Assis
authors.initials: OA
authors.lastname: Martins Filho
authors.forename: Andréa Teixeira
authors.initials: AT
authors.lastname: de Carvalho
authors.forename: Flávia Maria Lopes
authors.initials: FM
authors.lastname: Passos
mesh_terms: D000117:Acetylglucosamine / Q000378:metabolism; D000645:Ammonium Sulfate / Q000378:metabolism*; D017209:Apoptosis; D002473:Cell Wall / Q000378:metabolism; D003470:Culture Media; D007700:Kinetics; D007716:Kluyveromyces / Q000166:cytology / Q000254:growth & development* / Q000502:physiology
chemical_list: D003470:Culture Media; D000645:Ammonium Sulfate; D000117:Acetylglucosamine
keywords: Kluyveromyces lactis; aging signals; azote; continuous culture; culture en continu; growth rate; nitrogen; signaux de vieillissement; taux de croissance