Abstract
We studied the effect of molybdenum (Mo) concentration on transcription and translation of a putative Mo-storage protein (Mop) in the freshwater heterocystous cyanobacterium, Nostoc sp. PCC 7120. Triplicate treatments were acclimated to 1, 150, and 3000 nM Mo over an 11-day period (three transfers) and then transferred into 3000 nM Mo media. Growth rates in 1 nM treatments declined throughout the acclimation period and increased significantly after the final transfer into media containing 3000 nM Mo. After acclimation, cellular Mo content was highest in 3000 nM Mo treatments, intermediate in 150 nM treatments and lowest in 1 nM treatments (70 ± 30, 10.0 ± 0.04 and 2 ± 1 mg·gˉ1 dry biomass, respectively). Cellular Mo content converged on values of 20-40 mg·gˉ1 dry biomass after the final transfer into 3000 nM. Mop transcription and translation were up-regulated in 1 nM Mo treatments during the acclimation period, and down-regulated after transfer into 3000 nM Mo. Mop protein expression was only observed in 1 nM treatments after multiple transfers; minimal Mop protein was observed in 150 and 3000 nM Mo treatments. These observations suggest that Mop does not store excess intracellular Mo in Nostoc sp. PCC 7120, but may serve an unknown physiological function in Mo-limited metabolism.
Highlights
Molybdenum (Mo) is an essential trace element for all life, and is important for microbial acquisition of dinitrogen gas (N2) and nitrate ( NO3 ) due to its role as a co-factor in the enzymes nitrogenase and assimilatory nitrate reductase [1,2]
We studied the effect of molybdenum (Mo) concentration on transcription and translation of a putative Mo-storage protein (Mop) in the freshwater heterocystous cyanobacterium, Nostoc sp
Cellular Mo content was highest in the 3000 nM Mo treatments (70 ± 30 mg·g−1 dry biomass), intermediate in the 150 nM treatments (10.0 ± 0.04 mg·g−1 dry biomass) and lowest in the 1 nM treatments (2 ± 1 mg·g−1 dry biomass; Figure 1(b))
Summary
Molybdenum (Mo) is an essential trace element for all life, and is important for microbial acquisition of dinitrogen gas (N2) and nitrate ( NO3 ) due to its role as a co-factor in the enzymes nitrogenase and assimilatory nitrate reductase [1,2]. Some soil bacteria excrete Mo-chelating ligands (“molybdophores”) that solubilize Mo from minerals [11,12,13] and/or express alternative (though less efficient in terms of total electron flux required to fix one mol of N2) nitrogenases containing vanadium or iron in place of Mo [14]. The first, “MoSto” stores up to 90 atoms of Mo per protein molecule as an oxide mineral but is present in only a few strains of heterotrophic soil bacteria and purple non-sulfur bacteria [15,16]. Mop binds only 8 atoms of Mo per protein molecule [20,21,22], but is much more widespread in bacteria and archaea than MoSto. Mop may be an important microbial mechanism for combating Mo limitation in
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