Utilization of different nitrogen sources by the marine cyanobacteria Prochlorococcus and Synechococcus

Abstract

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 predominate in, but are not limited to, NO -depleted surface waters, where they outnumber coexisting Synechococcus populations. The niche parti-tioning by different Prochlorococcus ecotypes begs the question of whether they also differ in their nitrogen (N) utilization physiology, especially with respect to NO utilization. To explore this possibility, we studied the capa-Ϫ 3 bilities of different Prochlorococcus and Synechococcus strains to grow on a variety of N sources. We found that all the isolates grew well on NH and all were capable of urea utilization, occasionally at a lower growth rate. physiology and ecology. Thus, the utilization of different N sources in the marine environment is partitioned among closely related ecotypes, each with adaptations optimized for the environment where these sources are available.Since the first description of unicellular cyanobacteria as an abundant component of the marine phytoplankton community (Johnson and Sieburth 1979), the genus Synechococcus has been established as a major primary producer in the surface ocean. Synechococcus presence has been reported from waters in the (sub)tropics, temperate, and even polar regions and is often the dominant phytoplankter in both nutrient-deplete stratified, and nutrient-rich mixed waters (Par-

Response of Prochlorococcus ecotypes to co-culture with diverse marine bacteria

“…MED4 is a small cell with a highly streamlined genome, and is a member of the high-light adapted clade of Prochlorococcus. MIT9313, in contrast, is a slightly larger cell with a larger genome, and is better adapted for growth at the low light levels found deeper in the water column (Moore et al, 1998(Moore et al, , 2002Rocap et al, 2003;Bouman et al, 2006;Johnson et al, 2006;Coleman and Chisholm, 2007). Both strains are growing in these experiments below their respective temperature and light optima (although closer to those of MIT9313, (Rocap et al, 2003;Zinser et al, 2007)), but have been preacclimated to the experimental conditions for 47 months (B120 generations) and thus the difference in co-culture outcome is likely not caused by a general stress response in one strain because of culture conditions.…”

“…While Prochlorococcus have been extensively studied vis-a`-vis the role of environmental factors, such as light, temperature and nutrient availability in shaping their ecology (Moore et al, 1998(Moore et al, , 2002Bouman et al, 2006;Johnson et al, 2006;Coleman and Chisholm, 2007), and 'top down' processes, such as predation and viral lysis have also been studied to some degree (Lindell et al, 2005Sullivan et al, 2005;Frias-Lopez et al, 2009), systematic studies of their interaction with heterotrophic bacteria are limited to that of Morris and Zinser (Morris et al, 2008) described above, who focused on the growth-enhancing role of bacteria in low-density cultures of Prochlorococcus. Inspired by this work, and by systemic analyses of Long and Azam (2001), we undertook a broad-based and quantitative analysis of co-cultures of two axenic Prochlorococcus ecotypes (Saito et al, 2002;Moore et al, 2005) with hundreds of diverse heterotrophic bacteria, examining the response of the Prochlorococcus cells to the presence of bacteria over the entire growth curve of the cultures.…”

Cell surface acid-base properties of the cyanobacterium Synechococcus : Influences of nitrogen source, growth phase and N:P ratios

“…The results suggest that the primary cause of these changes was the presence of urea, and to a lesser extent ammonium, as the sole fixed nitrogen source. Nitrogen utilization by cyanobacteria has been widely studied in the past (Moore et al, 2002;Collier et al 2012), and altered gene expression in response to nitrogen utilization has been previously described (Hettero et al, 2001;Foster et al, 2007). For instance, Sakamoto et al (1999) suggested that the expression of both nrtP and narB genes that encode for nitrate/nitrite permease and nitrate reductase, respectively, in Synechococcus strain PCC 7002 are high in nitrate-containing media and low in media containing ammonium or urea.…”

Effects of high light on transcripts of stress-associated genes for the cyanobacteria Synechocystis sp. PCC 6803 and Prochlorococcus MED4 and MIT9313

“…Highlight-adapted genotypes occupy the upper, well-illuminated but nutrient-poor part of the water column whereas lowlight-adapted genotypes are preferentially found at the bottom of the illuminated layer but in a nutrient-rich environment. These ecotypes differ in their optimal light intensity for growth (Moore et al, 1998), pigment content (Moore et al, 1995), light harvesting efficiency, sensitivity to trace metals (Mann, 2002) and nitrogen utilization ability (Moore et al, 2002). Full genome information is available for Prochlorococcus MED4, which experiences growth in high light (HL) waters of the open oceans, and Prochlorococcus MIT9313, which typically grows in low light (LL) environments and is found deeper down in the water column (Rocap et al, 2003).…”