Parallel experiments with Thalassiosira rotula in outdoor plastic tanks: Development of dissolved free amino acids during an algae bloom

Micro-algae are thought to be involved in the turnover of pools of dissolved free amino acids (DFAA) in seawater either by their excretion or by the uptake of these compounds. Our study showed that, in vitro, 3 benthic diatom species were able to deplete small additions of individual Lamino acids down to concentrations below 10 to 40 nmol I-', as determined by HPLC. When nitrogen was limited, all test species scavenged their media for 10 or 11 amino acids added but Amphiprora cf. paludosa assimilated 3 amino acids also in the presence of surplus nitrate. Navicula salinarum took up all 10 amino acids supplied, whereas Nitzschia closterium assimilated none of them, when nitrate was present. Excretion of DFAA could not be detected in the medium of growing nitrate-sufficient cultures; N. clostenum, N. saljnaium and A. cf. paludosa excreted respectively less than 0.03, 0.05 and 0.1 Oh of the cellular nitrogen as amino acids. Only silicate deprivation induced A. cf. paludosa to excrete 1 % cellular nitrogen as DFAA. The results show that benthic diatom populations may act as net consumers of DFAA, even when the concentrations are as low as 100 to 1,000 nmol I-', the range reported for nearshore seawater and the porewater of mudflats.

Section: A Y Smentioning

confidence: 48%

Participation of diatoms in the amino acid cycle of coastal waters; uptake and excretion in cultures

Admiraal¹,

Laane²,

Peletier³

1984

“…Growing phytoplankton cells release minimal amounts of amino acids, but amino acids are released by senescent cells during post-bloom conditions (Hammer e t al. 1981, Poulet & Martin-Jezequel 1983, Hammer & Eberlein 1986, Hammer & Kattner 1986. DFAAs c a n ongin a t e from faecal pellets a wide spectrum of amino aclds.…”

Section: Discussionmentioning

confidence: 99%

Responses of copepods to dissolved free amino acids

Gill¹,

Poulet²

1988

ABSTRACT. The first maxilla (Ml) beating frequency of Temora longicornis, which is considered to be an index of feeding behaviour, was measured using a computerized micro-impedance technique, in filtered seawater as a control, and after exposure to 9 different particle-free mixtures of equimolar (10-' M) amino acids dissolved in seawater. Mixtures containing 20 dissolved free amino acids (ASP, GLU,

“…Furthermore, the time scales over which bacterial and phytoplankton production covary may change depending on the relative contribution of the various pathways by which phytoplankton carbon becomes available for bacterial consumption. Examples of these pathways include: continuous exudation by healthy algal cells (Sharp 1977); pulsed release by stressed or decaying phytoplankton blooms (Hammer & Eberlein 1981); release by zooplankton excretion (Bidigare 1983); or 'sloppy feeding' by zooplankton (Lampert 1978).…”

Section: Introductionmentioning

confidence: 99%

Unbalanced growth in natural assemblages of marine bacterioplankton

Chin-Leo¹,

Kirchman²

1990

113

We tested whether natural assemblages of marine bactenoplankton undergo periods when rates of macromolecular syntheses are uncoupled (unbalanced growth). In seawater cultures of bacteria, rates of DNA and protein syntheses (thymidine and leucine incorporation) and changes in the DNA amount and cell size were compared to fluctuations in growth rate. Rates of DNA and protein syntheses became uncoupled when the bacterial assemblage shifted between growth rates. During these periods of unbalanced growth, rates of bacterial protein synthesis changed faster than rates of DNA synthesis. Variations in the DNA concentration and size of cells paralleled changes in rates of DNA and protein syntheses. The C : DNA ratio of bacteria varied 2-fold depending on the growth state with an average value of 4.6 -t 0.48. The delay between unbalanced growth and shifts in the growth rate was on the order of hours and was always shorter than the generation time. Information about unbalanced growth may reveal the delay between fluctuations in the environment and the corresponding bacterial response. In addition, the unbalanced growth model may explain why rates of thymidine and leucine incorporation occasionally do not covary in pelagic ecosystems.