Knowledge of life on the Southern Ocean seafloor has substantially grown since the beginning of this century with increasing ship-based surveys and regular monitoring sites, new technologies and greatly enhanced data sharing. However, seafloor habitats and their communities exhibit high spatial variability and heterogeneity that challenges the way in which we assess the state of the Southern Ocean benthos on larger scales. The...

Summary Marine Synechococcus thrive over a range of light regimes in the ocean. We examined the proteomic, genomic and physiological responses of seven Synechococcus isolates to moderate irradiances (5–80 μE m −2 s −1 ), and show that Synechococcus spans a continuum of light responses ranging from low light optimized (LLO) to high light optimized (HLO). These light responses are linked to phylogeny and pigmentation. Marine sub...

We assessed the significance of cyanate utilization in marine primary productivity from the distribution of a dedicated transporter (encoded by cynABD ) in different ocean environments. Several lines of evidence indicate that the cyanate utilization potential is associated mainly with surface populations of Prochlorococcus . Spatial and temporal dimensions of cynA , cynS , and ntcA expression by picocyanobacteria in the northe...

Summary The above‐ground surfaces of terrestrial plants, the phyllosphere, comprise the main interface between the terrestrial biosphere and solar radiation. It is estimated to host up to 10 26 microbial cells that may intercept part of the photon flux impinging on the leaves. Based on 454‐pyrosequencing‐generated metagenome data, we report on the existence of diverse microbial rhodopsins in five distinct phyllospheres from ta...

Cyanate, a by‐product of urea decomposition, is a potential nitrogen (N) source in marine environments, but to date it has received scant attention. Cyanobacteria presumably acquire this compound via a substrate‐specific ABC‐type transporter ( cynABD ), and they convert it to ammonium and carbon dioxide by cyanase ( cynS ) activity. Participation of cyanate utilization genes in N‐stress responses in cyanobacteria has been impl...

The relationships among phytoplankton taxon‐specific phosphorus‐status, phytoplankton community composition, and nutrient levels were assessed over three seasons in the Gulf of Aqaba, Red Sea. During summer and fall, stratified surface waters were depleted of nutrients, and picophytoplankton populations comprised the majority of cells (80% and 88%, respectively). In winter, surface nutrient concentrations were higher and large...

Summary The cyanobacteria Synechococcus and Prochlorococcus are abundant primary producers in the nitrogen‐poor waters of the Gulf of Aqaba, northern Red Sea. Expression of the nitrogen regulatory gene ntcA is a useful indicator for determining the N‐status of cyanobacteria, and preliminary work with this gene suggests that it may also serve as a useful biodiversity marker. Here we investigated the genotypic diversity of ntcA...

Summary Unicellular cyanobacteria of the genus Synechococcus are a major component of the picophytoplankton and make a substantial contribution to primary productivity in the oceans. Here we provide evidence that supports the hypothesis that virus infection can play an important role in determining the success of different Synechococcus genotypes and hence of seasonal succession. In a study of the oligotrophic Gulf of Aqaba, R...

Summary Marine cyanobacteria of the genus Prochlorococcus belong to one of two ecotypes that are specifically adapted to either low light (LL) or high light (HL) conditions. Previous analyses of the differences in pigmentation and gene complement revealed that LL‐adapted ecotypes carry a gene cluster to produce a functional phycoerythrin, whereas in the fully sequenced genome of the HL‐adapted strain MED4, only a single and fr...

Summary Photosynthetic microorganisms play a crucial role in the marine environment. In vast areas of the oceans, marine primary productivity is performed by cells smaller than 2–3 µm (picoplankton). Here, we report on molecular analyses of the conserved photosynthetic psbA gene (coding for protein D1 of photosystem II reaction centre) as a diversity indicator of naturally occurring marine oxygenic picophytoplankton. The psbA...

Summary The expression of ftsZ , encoding the initiating protein of the prokaryotic cell division was analysed in natural Prochlorococcus populations in the Gulf of Aqaba, northern Red Sea. During the seasonal Prochlorococcus bloom in September 2000, picoplankton was collected from the deep chlorophyll maximum (DCM) at 2–4 h intervals over 3 consecutive days. Flow cytometric measurements as well as DNA sequence analyses showed...

Prochlorococcus is the most abundant phytoplankter throughout the photic zone in stratified marine waters and experiences distinct gradients of light and nitrogen nutrition. Physiologically and genetically distinct Prochlorococcus ecotypes partition the water column: high‐B/A (low‐light adapted) ecotypes are generally restricted to the deep euphotic zone near or at the nitracline. Low‐B/A (high‐light adapted) ecotypes predomin...

Depletion of phytoplankton cells and pigments over coral reefs was studied in the Gulf of Aqaba, Red Sea, during 1994–1996. Phytoplankton abundance and chlorophyll (Chl) a concentrations were 15–65% lower near the reefs than in the adjacent open waters. The decrease in chlorophyll near the reef was typically associated with an increase in the concentration of its degradation products, the pheopigments. The steepest slope of th...