Application of molecular techniques to addressing the role of P as a key effector in marine ecosystems

One of the fundamental questions of marine biology is what limits the growt h of marine organisms? Although there are many environmental variables that may impact on thsis problem, limitation for inorganic nutrients is a key c omponent. Recent examples in the literature provide good evidence for phosp horus (P) limitation of phytoplankton and bacterioplankton growth in severa l ocean regions. This review seeks to address new molecular methods that ma y be used to evaluate the P status of bacterial and algal groups in situ. P hysiological parameters of the photosynthetic apparatus and cell cycle vari ables are considered, but attention is focused on the development of protei n biomarkers that can be used to derive antibody probes for the immunologic al interrogation of natural microbial populations. The need to identify sui table protein markers in key genera, and for a good knowledge of the regula tion of the marker in the target organism to be obtained before assessing e xpression in natural populations, is emphasised. We also examine the role o f viruses, which are now widely accepted as being abundant in marine enviro nments, as a source of dissolved DNA, and hence an intermediate in P regene ration. Using molecular techniques, we present evidence that the availabili ty of P can influence virus-host interactions, with particular reference to viral lysogeny in marine Synechococcus spp.