FEMS MicrobiologyEcology73 (1990) 203-210 203 Published by Etseviex FEMSEC 00251 Maintenance requirements: energy supply from simultaneous endogenous respiration and substrate consumption H.H. Beeftink, R.T.J.M. van dcr H¢ijdcn and J.J. Heijnen Departmem ol Biochemical Engineerin& Delft Uniocr$ity of Technology, Delft. The Nedcerlands Received 20 April 1989 Revision receivedand accepted 12 Oclobcr 1999 Key words: Maintenance model, Pitt model; Herbert model 1. SUMMARY 2. INTRODUCTION A model is presented that describes energy for maintenance purposes (ATP) as being obtained simultaneously from biomass degradation as well as from substrate degradation in excess of growth requirements. The ratio between both catabolic processes was takers, to be growth rate dependent. As such, this approach is intermediate between established models; its stgnificant features are negative growth and the absence of substrate con- sumption at zero substrate concentration, and the attainability of the maximum specific growth rate (the model parameter ~,~) at elevated substrate concentrations. As a simple case, the amounts of ATP obtained from direct substrate catabolism or from the degradation of an equivalent amount of biomass were taken as identical. Also, the mainte- nance demand in terms of ATP per unit time and biomass was taken to be constant. True growth rate dependency of maintenance can be imple- mented by relaxing either of these assumptions. Correspondence to fPresent address): H.H. lteeftink, Depart- ment of Food Science, Food and Itioprocess Engineering Group, Agricultural University Wageningen,Bomenweg 2, 6703 riD Wa$cningen, The Netherlaad:. Mathematical expressions for the maintenance requirements of microorganisms are commonly formulated in two alternative ways. Herbert [;t] modified a common balance equatiolx on biomass reactions so as to contain a maintenance term in addition to a strictly growth-associated term. As an alternative, a conunon balance on substrate reactions was modified by Pitt [2]. The present contribution combines these approaches, and pos- tulates simultaneous modifications for both the balances on biomass and on substrate. A struc- tured metabolic mechanism is supplied to support the model equations. Although maintenance de- mands for reducing equivalents or for mass have been reported [3,4], the present model ¢onsid~s energy requirements only. The concept of Herbert [1], which was further elaborated upon by Man" et al., [5], assumes two fundamental reactions involving biomass and one reaction involving substrate. Although this shall be modified below, all reaction rates may be func- tions of the substrate concentrations s. ~,~,(s) = p~e(s) -- pc(s) (1) qo (s) = q (s) (2) Observed growth at a specific rate Pot~(s) thus 0168-6496/90/$03.50 © 1990 Federation of European MicrobiologicalSocieties Downloaded from https://academic.oup.com/femsec/article/6/3/203/539073 by guest on 21 June 2022