Competition between Specialist and Generalist Methylotrophic Bacteria for an Intermittent Supply of Methylamine

Abstract

A us t ralia (Received I9 June I986 ; revised 23 October 1986)A computer program, METHCOMP, to simulate the competition between an obligately methylotrophic bacterium, a facultatively methylotrophic bacterium, a bacterium able to use methylamine as nitrogen source only, and a non-methylamine-using bacterium for methylamine and glucose in continuous culture with a constant or alternating nutrient supply is described. Competitions between obligate methylotroph B6/2 and facultative methylotroph DT26 in continuous cultures supplied alternately with methylamine and glucose/ammonium were both simulated using experimentally determined growth parameters and investigated in laboratory mixed cultures. The results of the laboratory experiments were in excellent agreement with the simulations. The composition of the mixed population is predicted to vary with imposed dilution rate, with strain B6/2 excluded at dilution rates below 0.0625 h-l and strain DT26 excluded at dilution rates above 0.20 h-l. At intermediate dilution rates both strains coexisted in stable proportions which depended upon the dilution rate. Hence, the use of an alternating nutrient supply may offer a practical approach to the control of the composition of defined, mixed microbial populations. I N T R O D U C T I O NMixed microbial populations are the rule in many traditional food and drink fermentations but have been little exploited otherwise, in spite of potential advantages over axenic cultures, such as higher growth rate, higher yield, and greater stability (Harrison, 1978;Larsen et al., 1978). The development of new mixed culture processes is hampered by the absence of rational techniques for culture formulation and for controlling culture composition.One major aim of this work was to develop an experimental model system to study means of controlling the composition of mixed cultures by alternating the supply of two nutrients so as to favour each of two coexisting bacteria in turn. The system examined was based upon bacterial competition for methylamine, with glucose as the alternating nutrient. The second major aim of the work was to test certain hypotheses about the ecology of methylamine-using bacteria.Bacteria able to use methylamine under aerobic conditions include at least three main physiological types, namely (a) specialist, obligately methylotrophic bacteria able to use methylamine but not non-C, compounds as sole carbon and energy source; (6) generalist, facultative methylotrophs able to use methylamine or other compounds singly as sole carbon and energy source; and (c) methazotrophs which cannot use methylamine as sole carbon and energy source but, in the presence of another source of carbon and energy, can use it as sole nitrogen source. The existence of the methazotrophs adds an extra dimension to the model not possible

Experimental Evolution ofPseudomonas fluorescensin Simple and Complex Environments

“…As this substrate is depleted, types able to grow on lower concentrations will be favored, until at last only the single most frugal type remains (Tilman 1977). Organisms may differ in the ratio of resources that they require, however, and two or more different kinds may then coexist within a certain range of intermediate resource supply rates (Tilman 1977;Gottschal et al 1979Gottschal et al , 1981Laanbroek et al 1979;Dykhuizen and Davies 1980;Legan et al 1987; Brzezinski and Nelson 1988;Grover 1988). Resources of this kind cannot be substituted for one another: carbon, say, cannot be made to take the place of nitrogen.…”

Modelling of mixed chemostat cultures of an aerobic bacterium, Comamonas testosteroni, and an anaerobic bacterium, Veillonella alcalescens: comparison with experimental data

“…To this end, a mathematical model was constructed to describe the experimental mixed cultures in more detail, thus helping us understand the observed pattern of growth in response to various degrees of oxygen supply. The current model is a further elaboration of earlier models that is based on Monod-type growth kinetics and is used to describe both pure and mixed continuous cultures (10,12,19,38,41).…”

“…Mathematical model. The model is based on the assumption that substrate-dependent growth of bacteria in mixed culture can be described according to the same mathematical formulations as are used for the description of growth in pure cultures (10,12,18,19,28,38,41; see below also). The model was designed according to the following three basic steps.…”

Negative frequency‐dependent selection maintains coexisting genotypes during fluctuating selection

“…Coexisting resistant and vulnerable genotypes also can emerge in predator-prey experiments where predator frequency cycles over time (Bohannan et al 2002;Becks et al 2010). A number of experiments have demonstrated coexistence between different preexisting species in fluctuating environments (Legan et al 1987;Brzezinski and Nelson 1988;Rodríguez-Verdugo et al 2019). Outside of the evolution of cross-feeding, we are not aware of the de novo evolution of multiple co-existing genotypes from an experiment in which a single ancestral genotype was propagated under temporally fluctuating conditions.…”