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The environmental conditions under which rhizodia are grown, strongly influence their symbiotic and growth behaviour. Chemostat is an appropriate culture system for studying organisms response to nutrient-limited environments. The type of nutrient limitation can severely affect the efficiency of bacterial growth yields. It was previously reported that Mn 2+ affected rhizobial growth. The objective of this study was to obtain more information about the effect of Mn 2+ on growth characteristics of rhizobia. Rhizobium etli was grown in chemostat culture under either carbon (mannitol) or nitrogen (ammonium) limiting conditions using a synthetic culture medium. Both types of culture were carried out without added MnSO 4 or with a medium containing 1.0 μM of this salt. Carbon- or nitrogen-limited cultures without added MnSO 4 in the medium were shown to be growing under a double nutrient limitation. The absence of Mn 2+ had a great effect on the growth characteristics of R. etli . Yields on carbon substrate and on oxygen were much higher when cells were grown in a culture medium containing MnSO 4 . R. etli seemingly possesses two NADH dehydrogenases, which, in analogy with similar enzymes of Escherichia coli , have been tentatively named NDH-1 and NDH-2. Cells grown without added MnSO 4 lacked NDH-1 activity, whereas in cells grown in the presence of 1.0 μM MnSO 4 this enzyme was active. |
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