Characterization of growth and metabolism of the haloalkaliphile Natronomonas pharaonis

Natronomonas pharaonis is an archaeon adapted to two extreme
conditions: high salt concentration and alkaline pH. It has become
one of the model organisms for the study of extremophilic life.
Here, we present a genome-scale, manually curated metabolic
reconstruction for the microorganism. The reconstruction itself
represents a knowledge base of the haloalkaliphile's metabolism
and, as such, would greatly assist further investigations on
archaeal pathways. In addition, we experimentally determined
several parameters relevant to growth, including a characterization
of the biomass composition and a quantification of carbon and
oxygen consumption. Using the metabolic reconstruction and the
experimental data, we formulated a constraints-based model which we
used to analyze the behavior of the archaeon when grown on a single
carbon source. Results of the analysis include the finding that
Natronomonas pharaonis, when grown aerobically on acetate, uses a
carbon to oxygen consumption ratio that is theoretically
near-optimal with respect to growth and energy production. This
supports the hypothesis that, under simple conditions, the
microorganism optimizes its metabolism with respect to the two
objectives. We also found that the archaeon has a very low carbon
efficiency of only about 35%. This inefficiency is probably due to
a very low P/O ratio as well as to the other difficulties posed by
its extreme environment.