Dissolved organic phosphorus compounds

Utilization of phosphate monoesters by microalgae and bacteria is effected by phosphomonoesterases (phosphatases) of broad specificity present at the cell surface. Hydrolytic release of PO4- from sugar phosphates, nucleotide phosphates, phospholipids, and phenyl phosphates, to name a few, enables a wide variety of phosphorus containing compounds to be utilized as phosphorus sources for growth of microbes. Ultrastructural observations and results from biochemical experiments indicate that extracellular phosphatases cleave the phosphate moiety from dissolved organic phosphorus compounds, which is then internalized, leaving the carbon skeleton outside the cell (Kuenzler and Perras, 1965 Doonan and Jensen, 1977). 

Variety of Dissolved Organic Phosphorus Compounds in Aquatic Environments... 

Heath, R.T. (1985) Dissolved organic phosphorus compounds do they satisfy planktonic phosphate demand in summer Canadian Journal of Fisheries and Aquatic Sciences 43, 343-350. 

Siuda, W. and Chrost, R.J. (2001) Utilization of selected dissolved organic phosphorus compounds by bacteria in lake water under nonlimiting orthophosphate conditions. Polish Journal of Environmental Studies 1 0, 475 83. 

Hong HS, Wang HL, Huang BQ (1995) The availabiUty of dissolved organic phosphorus compounds to marine phytoplankton. Chin J Oceanol Limnol 13(2) 169-176... 

For these reasons, numerous attempts have been made to identify and characterize DOP, but with little success because it is usually present in very low concentrations. Typical values in lake waters range from 5 to 100 xg of P/L in oligotrophic to eutrophic systems. Colorimetric methods have been used extensively to detect and differentiate between soluble reactive phosphorus (SRP) and soluble unreactive phosphorus (SUP) at concentrations as low as 10 xg of P/L (I). SRP is generally considered to consist of only orthophosphate compounds, whereas SUP is composed of all other phosphorus species, primarily organic phosphorus compounds. The sum of SRP and SUP is equal to the total soluble phosphorus (TSP). These methods were used to study the dynamics of bulk phosphorus fractionation between the sediments, suspended particulate matter, the biota, and the dissolved fraction (2). Despite these studies, very little is known regarding the identity and characteristics of the DOP in the hydrosphere. 

Dissolved organic phosphorus a subcomponent of all the phosphorus-containing dissolved organic compounds in dissolved organic matter (e.g., phosphonates). 

Like other dissolved organic nutrients, the chemical composition of organic P is relatively unknown. Marine dissolved organic phosphorus (DOP) composition has been mostly identified as particular compound classes such as monophosphate esters, phosphonucleotides, nucleic acids, phospholipids, phosphonates and polyphosphates (Benitez-Nelson, 2000). Kolowith et al. (2001) found that monophosphate esters and phosphonates are major components in the Pacific Ocean, the Atlantic Ocean and the North Sea. ATP (adenosine triphosphate), ubiquitous in aU living cells, has been used as a model DOP compound in radiotracer experiments to obtain information on P sources and fluxes in natural environments (Bjorkman et al., 2000 Karl and Bossard, 1985) and cyanobacterial cultures (Fu et al., 2006). 

Very little detail is known about the nitrogen and phosphorus cycles. Dissolved orthophosphate is taken up in plant growth and returned eventually after serving in cell fluids and tissues. It appears to be released primarily in the form of organophosphorus compounds, and at certain seasons of the year more than half the phosphorus in the water is described as "dissolved organic phosphorus. Yet as of a year or so ago... 

Cotner, J.B. and Wetzel, R.G. (1992) Uptake of dissolved inorganic and organic phosphorus compounds by phytoplankton and bacterio-plankton. Limnology and Oceanography 37, 232-243. 

Notwithstanding the impressive enhancement in the rates of hydrolysis of many organic phosphorus compounds by dissolved metal ions, because of the generally low concentration of most dissolved metal ions in the environment, homogeneous catalysis will only be an important pathway for organic phosphorus breakdown in unusual circumstances (Smolen and Stone, 1997). 

Although aquatic biochemical ecologists have focused nearly exclusively on lytic processes for dissolved organic phosphorus utilization, heterotrophic bacteria can directly take up certain organic phosphorus compounds from their surrounding environment without prior hydrolysis (Table 9.2). E. coli is known to have two different processes by which glycerol 3-phosphate can be taken up without prior hydrolysis... 

OTHER TECHNIQUES A number of other techniques have been used to determine specific organic phosphorus compounds in the environment, including a firefly luciferase assay for adenosine di- and triphosphate (Kaplan and Bott, 1985), a protein assay for cyclic adenosine monophosphate (Francko and Wetzel, 1982) and cetryltrimethylammonium bromide precipitation of dissolved RNA and DNA in marine and freshwaters (Karl and Bailiff, 1989). However, none of these are regularly used in studies of organic phosphorus dynamics in aquatic ecosystems. 

Separate quantitative determination of orthophosphate, hydrolyzable phosphates and organic phosphorus compounds is not possible with the means offered by conventional water analysis if these substances are present together in dissolved form, since in the course of hydrolysis not only orthophosphates but also organic phosphate compounds are partially codetected. 

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