Molecular ecology of the marine cyanobacterial genera Prochlorococcus and Synechococcus
David J. Scanlan Ã , Nyree J. West
Department of Biological Sciences, University of Warwick, Coventry CV4 7AL, UK Received 4 September 2001 ; received in revised form 14 December 2001 ; accepted 17 December 2001 Firstpublished online 31 January 2002
Oxygenic photoautotrophs of the genera Synechococcus and Prochlorococcus contribute significantly to primary production and are now widely accepted as the most abundant members of the picophytoplankton in the world’s oceans. Since they represent one of the few cultured and representative groups of marine microorganisms, study of their physiology andbiochemistry has progressed rapidly since their discovery. The recent and on-going sequencing of the complete genomes of representative strains will further hasten our understanding, and allow a complete interrogation, of the metabolism of these organisms. Moreover, since they inhabit a relatively simple environment they provide an excellent model system to begin to identify the underlying molecularmechanisms which allow their success in water columns with large vertical gradients of light and nutrients. Such work should provide novel insights into the genetic adaptations of these important marine microbes to their environment. We review here molecular ecological methods that are already available or which are currently being developed for these organisms. Such methods allow communitystructure, growth rate and nutrient status analysis, potentially at the single cell level, and can be used to define the niches, or identify the biotic or abiotic factors, which might control the productivity of specific genotypes. These techniques will undoubtedly provide the tools for answering more discerning questions concerning their ecology. How the complete genome sequence information isproviding insights, and can further facilitate our understanding, of the ecology of these organisms is also discussed. ß 2002 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights reserved.
1. Introduction The discovery of tiny, single-celled cyanobacteria as ubiquitous and abundant components of the marine microbiota has radically changed our view of thefunctioning and composition of marine ecosystems. It is now clear that the two genera Prochlorococcus and Synechococcus dominate the photoautotrophic picoplankton over vast tracts of the world’s oceans where they occupy a key position at the base of the marine food web and contribute signi¢cantly to global primary productivity [1,2]. Although they often co-occur, they exhibit di¡erent spatialdistributions on a worldwide and a local scale. Synechococcus are distributed ubiquitously throughout oceanic regions, ranging from polar through temperate to tropical waters and are generally more abundant in nutrient-rich
* Corresponding author. Tel. : +44 (24) 76 528363; Fax: +44 (24) 76 523701. E-mail address : firstname.lastname@example.org (D.J. Scanlan).
surface waters, whilst Prochlorococcusare largely con¢ned to a 40‡N^40‡S latitudinal band, being generally absent from brackish or well-mixed waters. Prochlorococcus also generally extend deeper in the water column than Synechococcus . Synechococcus was ¢rst detected earlier than Prochlorococcus by virtue of their intense orange phycoerythrin £uorescence , and it was only in the late 1980s that sensitive £ow cytometers wereable to detect the dim red £uorescence emitted by the unique divinyl derivatives of chlorophyll a and b (chl a2 and chl b2 ) of Prochlorococcus [5,6]. Since their discovery, several studies of cultures and natural populations of Prochlorococcus and Synechococcus have indicated that these populations could be both genetically and physiologically diverse. A wide variety of molecular approaches have...