Abstract
Paracoccus denitrificans is a well studied model organism with respect to its aerobic and anaerobic respiratory enzymes. However, until now, the growth medium for this organism has not been optimized for anaerobic growth. In particular, the requirements of P. denitrificans for trace elements (TEs) are not well known. In the present study we aimed to improve growth rates of P. denitrificans Pd1222 on a defined medium under anoxic conditions. We designed media containing different combinations of TEs at various concentrations, and tested their performance against previously reported media. Our results suggest that growth rate and yield depend on the availability and concentration of TEs in the medium. A chelated TE solution was more suitable than an acidified TE solution. Highest growth rates were achieved with medium comprising the TEs iron, manganese, molybdenum, copper and zinc ranging from 0.1 to 9 μM. On this medium, P. denitrificans Pd1222 grew with a generation time of 4.4 h under anoxic conditions and 2.8 h under oxic conditions. Diauxic growth was clearly shown with respect to nitrate and nitrite reduction under anoxic conditions.
Highlights
The first strain of Paracoccus denitrificans was isolated from soil more than one century ago by Beijerinck and Minkman (1910)
P. denitrificans is a model organism for denitrification, we found that the growth media and trace elements (TEs) solutions described for this organism enabled only very poor anaerobic growth of P. denitrificans Pd1222
TE1 is characterized by high metal concentrations between 1.8 and 36 μM and contains ethylenediaminetetraacetic acid (EDTA) as a chelator to keep the metals dissolved, while metals in TE-2 are 4 to more than 1000 times lower concentrated and metal dissolution is achieved by lowering the pH instead of adding EDTA
Summary
The first strain of Paracoccus denitrificans (synonym Micrococcus denitrificans) was isolated from soil more than one century ago by Beijerinck and Minkman (1910). It was shown to grow aerobically and anaerobically performing complete or partial denitrification. Cultivation conditions have an important influence onto the physiological phenotype of an organism. Prominent examples for physiological processes that are strongly influenced by cultivation are the aerobic oxidation of methane (Stanley et al, 1983; Prior and Dalton, 1985) and methanol, the fixation of nitrogen gas (Lehman and Roberts, 1991), and the assimilation of CO2, which make use of different enzymes (or even pathways) depending on the composition of the growth medium [most notably the presence or absence of vitamins and trace elements (TEs)]. It is important to improve cultivation conditions of an organism and prevent its growth inhibition to avoid misinterpretation of the observed phenotypes
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