COBIOT-857; NO. OF PAGES 7 Please cite this article in press as: Shapiro OH, Kushmaro A. Bacteriophage ecology in environmental biotechnology processes, Curr Opin Biotechnol (2011), doi:10.1016/j.copbio.2011.01.012 Available online at www.sciencedirect.com Bacteriophage ecology in environmental biotechnology processes Orr H Shapiro and Ariel Kushmaro Heterotrophic bacteria are an integral part of any environmental biotechnology process (EBP). Therefore, factors controlling bacterial abundance, activity, and community composition are central to the understanding of such processes. Among these factors, top-down control by bacteriophage predation has so far received very limited attention. With over 10 8 particles per ml, phage appear to be the most numerous biological entities in EBP. Phage populations in EBP appear to be highly dynamic and to correlate with the population dynamics of their hosts and genomic evidence suggests bacteria evolve to avoid phage predation. Clearly, there is much to learn regarding bacteriophage in EBP before we can truly understand the microbial ecology of these globally important systems. Address Ben Gurion University of the Negev, Biotechnology Engineering, POb 653, Beer sheva 84105, Israel Corresponding author: Shapiro, Orr H (shapiroo@bgu.ac.il) Current Opinion in Biotechnology 2011, 22:1–7 This review comes from a themed issue on Environmental biotechnology Edited by Lindsay Eltis and Ariel Kushmaro 0958-1669/$ – see front matter # 2011 Elsevier Ltd. All rights reserved. DOI 10.1016/j.copbio.2011.01.012 Introduction Heterotrophic bacteria are an integral part of any environ- mental biotechnology process (EBP). This is particularly true for wastewater treatment processes (WWTP), where bacteria play key roles in nutrient removal and the trans- formation and mineralization of organic matter. Therefore, factors controlling bacterial abundance, activity, and com- munity composition are central to the understanding of such processes. Among these factors, top-down control through viral lysis has so far received very limited attention. Bacteriophage (viruses attacking bacteria) are considered to be the most abundant and diverse biological entities on earth, with ten phages for every bacterial cell in most studied ecosystems [1  ]. The strong predation pressure exerted by phage on microbial communities means that bacterial fitness is measured by their adaptation not only to available resources but also to the biotic environment [2  ]. Bacteriophage are therefore continuously regulating microbial ecology and activity, including carbon and nutrient fluxes, food web dynamics, and microbial diver- sity and diversification [3,4  ]. While the number of studies directed towards bacteriophage ecology in aquatic systems is rapidly rising over the past decade, surprisingly few studies target phage ecology in WWTP. The current review aims to bring the reader up-to-date with what little is known, introduce some theories regarding possible effects of phage activity on WWTP microbial ecology and suggest possible directions for future study. Viruses in wastewater treatment processes Viruses, including bacteriophage, are long known to be found in EBP such as activated sludge WWTP [5] but most studies in this field either disregard them comple- tely or focus on the detection of viral particles in treated wastewater as indicators of survival and release of patho- genic viruses into the environment [6–8]. Bacteriophage ecology in WWTP was first considered in two separate studies published three decades ago [9,10], yet a search of the scientific literature today still returns less than 20 publications specifically targeting this subject. Con- sequently, our knowledge and understanding of phage ecology in WWTP, and their potential influence on these globally important processes, are still inadequate. How many are there? When studying phage in the environment, this is often one of the first questions asked. While the answer in itself does little to promote our understanding of phage ecology, it gives a measure of their significance in the microbial process (the more there are the more important they must be) and enables back-of-the-envelope calcu- lations resulting in impressively big numbers. Indeed, it was the number of phage in the environment that first drew the attention of the scientific community to their central place in microbial ecology [4  ,11,12]. Otawa et al. applied epifluorescence microscopy (EFM) to estimate total viral counts in 18 full scale activated sludge bioreactors, reporting viral concentrations of 10 8 to 10 9 virus like particles (VLP)/ml. Similar values were obtained for a municipal wastewater treatment plant in Singapore [13] and for a continuous flow, two stage bioreactor in Israel [14  ]. These studies suggest viral abundance in activated sludge to be higher than any other environment studied to date [15]. The ratio of VLP to bacterial cells in WWTP was shown to approxi- mate 10:1 [14  ], that is, similar to values obtained from www.sciencedirect.com Current Opinion in Biotechnology 2011, 22:1–7