Abstract
In their natural habitats, microorganisms are often exposed to periods of starvation if their substrates for energy generation or other nutrients are limiting. Many microorganisms have developed strategies to adapt to fluctuating nutrients and long-term starvation. In the environment, ammonia oxidizers have to compete with many different organisms for ammonium and are often exposed to long periods of ammonium starvation. We investigated the effect of ammonium starvation on ammonia-oxidizing archaea (AOA) and bacteria (AOB) enriched from freshwater lake sediments. Both AOA and AOB were able to recover even after almost two months of starvation; however, the recovery time differed. AOA and AOB retained their 16S rRNA (ribosomes) throughout the complete starvation period. The AOA retained also a small portion of the mRNA of the ammonia monooxygenase subunit A (amoA) for the complete starvation period. However, after 10 days, no amoA mRNA was detected anymore in the AOB. These results indicate that AOA and AOB are able to survive longer periods of starvation, but might utilize different strategies.
Highlights
In natural systems, the majority of microorganisms exist in a physiological state similar to a stationary phase [1]
In AOB, this process is catalyzed by the enzymes ammonia monooxygenase (Amo) and hydroxylamine oxidoreductase (Hao) [2]
The mechanism of ammonia starvation in AOB has not been fully elucidated; previous work demonstrated that ammonia monooxygenase subunit A (amoA) mRNA and 16S rRNA stability, as well as the stability of the Amo protein, during starvation may play a critical role in their survival and rapid recovery [4,7,12]
Summary
The majority of microorganisms exist in a physiological state similar to a stationary phase [1]. Nutrients become available in short pulses or are present in low concentrations. To survive these periods of starvation, microbes must be able to respond rapidly to fresh nutrients when they become available. Ammonia-oxidizing archaea and bacteria (AOA and AOB) are two groups of organisms that often encounter substrate starvation in the environment. Both AOB and AOA use the oxidation of ammonia to nitrite for the generation of energy. The first step of ammonia oxidation in AOA is catalyzed by Amo; the subsequent steps of the reaction remain uncharacterized [3]. The mechanism of ammonia starvation in AOB has not been fully elucidated; previous work demonstrated that amoA mRNA and 16S rRNA stability, as well as the stability of the Amo protein, during starvation may play a critical role in their survival and rapid recovery [4,7,12]
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