Most probable number quantification of hypophosphite and phosphite oxidizing bacteria in natural aquatic and terrestrial
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S H O R T CO M MU N I C A T I O N
Most probable number quantiWcation of hypophosphite and phosphite oxidizing bacteria in natural aquatic and terrestrial environments Brandee L. Stone · Andrea K. White
Received: 4 June 2011 / Revised: 28 September 2011 / Accepted: 10 November 2011 / Published online: 2 December 2011 © Springer-Verlag 2011
Abstract Concentrations of hypophosphite and phosphite oxidizing bacteria were found to be high, relative to bacterial concentrations growing on phosphate, in sediment and soil during winter and summer seasons from 12 common terrestrial and aquatic sites using a most probable number method. The percent of total culturable bacterial concentrations that could use these reduced phosphorus compounds as a sole source of phosphorus were as follows: hypophosphite, 7–100%; phosphite, 10–67%; aminoethylphosphonate, 34–270%. The average MPN/g (§SEM) was as follows: phosphate, 6.19 £ 106 (§2.40 £ 106); hypophosphite, 2.61 £ 106 (§1.35 £ 106) phosphite, 1.91 £ 106 (§1.02 £ 106); aminoethylphosphonate, 3.90 £ 106 (§ 1.95 £ 106). Relatively high concentrations of reduced phosphorus oxidizing bacteria were found in both pristine sites and sites with urban and agricultural disturbance. Concentrations of reduced phosphorus oxidizing bacteria in anoxic sediments and soil were equivalent. Our data indicate that reduced phosphorus oxidizing bacteria are abundant in the environment and provide strong evidence for the importance of bacterial P oxidation in nature. Keywords Reduced phosphorus oxidation · Phosphorus cycle · Nutrient cycling · Hypophosphite · Phosphite · Microbial metabolism
Communicated by Erko Stackebrandt. B. L. Stone · A. K. White (&) Department of Biological Sciences, California State University, 400 West First Street, Chico, CA 95929-0515, USA e-mail: [email protected]
Introduction A common misconception is that phosphorus (P) is inert to biological oxidation and reduction despite clear evidence that bacteria are able to oxidize and reduce P compounds (Metcalf and van der Donk 2009; White and Metcalf 2007). It is perhaps as a result of this misconception that bacterial oxidation of reduced P compounds and the impact of this activity on P biogeochemistry have largely been overlooked. In contrast to other biogeochemical cycles (e.g., nitrogen, sulfur, mercury, arsenic), in which redox reactions carried out by bacteria are central, the role of bacteria in the currently accepted P cycle is limited to the inter-conversion of Pi and Pi-containing compounds (e.g., phosphate esters) through the degradation of organic matter, in which P remains in its most oxidized state (P oxidation state +5). Phosphorus, particularly inorganic phosphate (Pi, P oxidation state +5), is essential to all living organisms, yet, Pi is often a limiting nutrient in the natural environment and microbes will often face P starvation. While it is true that the majority of P compounds identiWed in the environment contain fully oxidized P, reduced organic P compounds such as phosphonates (P oxidation state +3) and
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