Amino acid uptake of Prochlorococcus spp. in surface waters across the South Atlantic Subtropical Front

Abstract

To test the hypothesis that surface-living Prochlorococcus spp. (Pro) cyanobacteria metabolism declines towards the boundaries of its natural habitat, a latitudinal transect of surface waters was sampled from the centre of the Southern Atlantic Gyre (SAG, 20 to 35°S) to the South Subtropical Frontal Zone (SSFZ, 35 to 45°S). Along this transect, amino acid uptake rates of Pro, Synechococcus spp. (Syn) and an average bacterioplankton cell were determined using 35 S-methionine precursor and flow-cytometry sorting, with methionine uptake rate as an index of cellular metabolic activity. Methionine and possibly other amino acids were a very minor nutrient source for Syn, while their contribution to Pro production was significant. Contrary to expectations, the mean methionine uptake rate per Pro cell in the SSFZ was about 3 times higher than in the SAG. The uptake rates per unit Pro biomass were equal to or higher than that of an average bacterioplankton cell in both the SAG and SSFZ. About 20 and 5% of total bacterioplankton consumption of amino acids could be assigned to Pro in the SAG and SSFZ, respectively. Methionine and leucine turnover rates were 3.5 and 3 times higher in the SSFZ than in the SAG, respectively. These results suggest that Pro remained highly metabolically active and acquired more methionine at its habitat boundaries, despite higher rates of bacterioplankton activity and therefore greater competition, as well as exposure to deep water mixing, low light and low temperature conditions. KEY WORDS: Cyanobacteria · Prochlorococcus · Synechococcus · Bacterioplankton · Flow cyto-metric sorting · Bioassay · Isotopic tracer Resale or republication not permitted without written consent of the publisherAquat Microb Ecol 40: [241][242][243][244][245][246][247][248][249] 2005 nitrogen in the form of amino acids (Zubkov et al. 2003). The uptake of amino acids as well as other organic nitrogen could provide an additional source of macronutrients to be used in protein synthesis, and make Pro, in particular, photo-organotrophs.In the present study we determined the amino acid uptake by Pro and Syn in an attempt to find a physiological explanation for the dramatic shift between Proand Syn-dominated surface waters across the South Atlantic Subtropical Front. We hypothesised that surface-living Pro cyanobacteria metabolism based on the specific uptake of methionine declines towards the boundaries of its natural habitat. MATERIALS AND METHODSSampling site. The study was carried out on board the RRS 'James Clark Ross' (Cruise No. JR91) in September and October 2003. Surface seawater samples were generally collected at 5 to 7 m depth with a rosette of 20 l Niskin bottles mounted on a conductivity-temperature-density (CTD) profiler. Total bacterioplankton and cyanobacteria abundance reported herein were determined at 17 stations ( Fig. 1), microbial turnover rates of the amino acids, methionine (met) and leucine (leu) were determined at 13 stations, and group flow-sorting of Pro, Syn and an average bacterio...

Fine-scale variability in methanol uptake and oxidation: from the microlayer to 1000 m

“…Zubkov and co-workers demonstrated that Prochlorococcus use organic nitrogen compounds, e.g. amino acids (Mary et al, 2008;Zubkov and Tarran, 2005;Zubkov et al, 2003Zubkov et al, , 2004, whilst sulphur uptake from dimethylsulfoniopropionate has also been demonstrated (Vila-Costa et al, 2006). The uptake of glucose by Prochlorococcus has also more recently been suggested by Gómez-Baena et al (2008) as the first example of an organic molecule containing only carbon skeletons, i.e.…”

Changing bacterioplankton growth characteristics on a large spatial scale: oligotrophic versus mesotrophic ocean

“…In addition to substrate supply, the possible impact of picocyanobacteria (Synechococcus and Prochlorococcus) on TLi:TTi ratios must be considered (Zubkov et al 2000, Zubkov & Tarran 2005. Several species of cyanobacteria have been reported to incorporate leucine but not thymidine (Bern 1985, Kamjunke & Jähnichen 2000, Hietanen et al 2002.…”

Towards a better understanding of microbial carbon flux in the sea*

“…Mixotrophy is known to be common among eukaryotic phytoplankton (i.e. dinoflagellates and ciliates), but significant amino acid uptake was recently also documented in Prochlorococcus, the main prokaryotic primary producers of tropical and subtropical oceans (Zubkov & Tarran 2005). In the year 2000, 2 independent studies documented a widespread ability to utilize light energy among marine bacteria (Béjà et al 2000, Kolber et al 2000.…”

“…Fenchel 2001, Karl 2002) and dissolved and particulate organic matter (DOM and POM) is used by prokaryotes that were previously considered to be strictly phototrophic (e.g. Zubkov et al 2003, Zubkov & Tarran 2005, VilaCosta et al 2006, Unrein et al 2007, that chemoautotrophic metabolisms seem to dominate even in well-oxygenated areas of the deep ocean , and that coastal ocean carbon metabolism mediated by bacteria might include lithoheterotrophic metabolisms (Moran & Miller 2007), etc. Considering this, how should we depict the microbial food web?…”