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Title: The biochemical ecology of freshwater modular systems : the role of amino acids and humic substances.
Author: Eaton, Philip.
ISNI:       0000 0001 3437 616X
Awarding Body: University of Sussex
Current Institution: University of Sussex
Date of Award: 1995
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1. Free amino acid (faa) and humic substance (HS) concentrations were measured seasonally using high performance liquid chromatography (HPLC) in two contrasting freshwater ecosystems. FAA concentrations were generally higher in the eutrophic Lewes Brooks than in the oligotrophic Isle of Thorns lake, whereas the converse was the case with HS concentration. 2 Faa and HS accumulation patterns were measured in media conditioned by Ceratophyllum demersum alone, Biompha/aria g/abrata alone, and media conditioned by the snail and plant together. It was hypothesised that nutrient exchange may benefit the modular components and that HS may also provide benefits by acting as a growth factor or as a protective shield. 3 Total faa (tfaa) and HS accumulated at a significantly higher rate in axenic compared to non-axenic Lemna cultures. This seems to be the first clear report of HS formation without bacterial involvement. Tfaa concentrations accumulated at a significantly higher rate in the axenic Lemna system, most probably due to the absence of bacteria. 4 The rate of accumulation of exogenous faa in snail conditioned media (SCM) decreased with temperature and oxygen availability, and displayed saturable kinetics. 5 B. g/abrata tissue faa were shown to act as osmolytes. Thus their cellular faa concentrations increased proportionately with rises in environmental osmolarity. 6 The exogenous faa medleys that accumulated in SCM were shown by statistical methods to be species specific. These medleys may therefore serve as sources of information and could have a role in chemotaxonomy. 7 B. g/abrata was capable of inward net accumulation of exogenous amino acids, including a non-metabolisable amino acid analogue - aminoisobutyric acid (AlB). 8 The experimental evidence suggested that AlB was accumulated by B. g/abrata via an active amino acid transport system. The transport system had a low Vmax (15.4 nmol/g/hr) and a Km of 20.6 f.lM, a concentration similar in magnitude to that measured in natural sediments (chapter 2). Inward transport of exogenous faa was calculated to meet 0.24 % of basal metabolism, and thus has a limited nutritional role.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Biochemistry