Abstract
Nodularia spumigena is a nitrogen-fixing cyanobacterium that forms toxic blooms in the Baltic Sea each summer and the availability of phosphorous is an important factor limiting the formation of these blooms. Bioinformatic analysis identified a phosphonate degrading (phn) gene cluster in the genome of N. spumigena suggesting that this bacterium may use phosphonates as a phosphorus source. Our results show that strains of N. spumigena could grow in medium containing methylphosphonic acid (MPn) as the sole source of phosphorous and released methane when growing in medium containing MPn. We analyzed the total transcriptomes of N. spumigena UHCC 0039 grown using MPn and compared them with cultures growing in Pi-replete medium. The phnJ, phosphonate lyase gene, was upregulated when MPn was the sole source of phosphorus, suggesting that the expression of this gene could be used to indicate the presence of bioavailable phosphonates. Otherwise, growth on MPn resulted in only a minor reconstruction of the transcriptome and enabled good growth. However, N. spumigena strains were not able to utilize any of the anthropogenic phosphonates tested. The phosphonate utilizing pathway may offer N. spumigena a competitive advantage in the Pi-limited cyanobacterial blooms of the Baltic Sea.
Highlights
Phosphorus is an essential macronutrient for life, being a key component in organic biomolecules, such as DNA, proteins, and phospholipids
We amplified phnD and phnJ genes from the environmental samples collected from the Baltic Sea using the N. spumigena-specific phnD and phnJ primers demonstrating that these genes are abundant in the Gulf of Finland and the Baltic Proper (Fig. 1c)
We demonstrate that strains of N. spumigena can grow using methylphosphonate as a sole source of phosphorous with only minor remodeling of the transcriptome
Summary
Phosphorus is an essential macronutrient for life, being a key component in organic biomolecules, such as DNA, proteins, and phospholipids. The most preferable form of phosphorus for the uptake by cyanobacteria is orthophosphate ions H2PO42−, HPO42−, and PO43− (Pi), which occur. Pi is usually found at very low concentrations in environment and lack of Pi is the main growth-limiting factor for nitrogen-fixing and phototrophic cyanobacteria during blooms in aquatic ecosystems [10,11,12]. 100.5 evolved specific strategies to enhance phosphorus availability under Pi-limited conditions [13, 14]. The highaffinity phosphate transport system, encoded in the pstABCS operon, is the most studied system for Pi uptake. The pstABCS operon belongs to the pho regulon, which is activated by autophosphorylation when the Pi concentration is low [15,16,17]. The PstABCS complex ensures rapid and effective scavenging of Pi in phosphorus-limiting conditions
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