GERBAM — Deuxième Colloque International de Bactériologie marine — CNRS, Brest, 1-5 octobre 1984
IFREMER, Actes de Colloques, 3, 1986, pp. 103-108
11
EVALUATION OF THE HETEROTROPHIC ACTIVITY IN WATERS BY MICROANALYTICAL METHODS
R. BERTONI
CNR - Istituto Italiano di Idrobiologia, Pallanza, (ITALY).
ABSTRACT - The radiochemical methods proposed for evaluating heterotrophic activity in waters have been
severely criticized in recent years because they are not considered to be sufficiently realistic. Thus, the possibility
of directly measuring the heterotrophic consumption of naturally occurring Organic Carbon (OC) in fresh water
samples incubated under controlled conditions has been evaluated. The analytical performances of two OC
analyzers utilizable for this purpose are discussed here, and some examples of the results obtained by the direct
measurement of OC consumption are presented. The consumption rates thus measured range from 11.6 to
50.2 µgC/ 1.h. Although the technique discussed here is less sensitive than radiochemical methods, the few
assumptions needed when making a direct measurement largely offset this loss of sensitivity.
Key words : heterotrophic activity, organic carbon cycle, organic microanalysis.
RÉSUMÉ - Les méthodes consistant à estimer l’activité hétérotrophe à partir de mesures d’incorporation de
substrats radioactifs ont été critiquées dans ces dernières années parce que insuffisamment proches de la réalité.
Pour obtenir une estimation plus représentative, on a essayé de mesurer directement la consommation
hétérotrophe du carbone organique naturellement présent dans les eaux sur des échantillons incubés en
conditions contrôlées. Les potentialités analytiques de deux instruments utilisables pour ce but sont ici illustrées
et des résultats obtenus par la mesure directe de la consommation hétérotrophe du carbone organique sont
présentés. Dans les lacs étudiés on a mesuré des vitesses de consommation du substrat naturel comprises entre
11.6 et 50.2 µg C/l.h. Bien que cette technique soit moins sensible que les méthodes radiochimiques, elle
n’implique pas des hypothèses difficiles à vérifier et cet avantage compense largement sa moindre sensibilité.
Mots clés : activité hétérotrophe, cycle du carbone organique, microanalyse organique.
INTRODUCTION
It is essential for those concerned with the heterotrophic processes within the Organic
Carbon (OC) cycle to know the total OC flow through the decomposer microheterotrophs. For this purpose the methods which evaluate the microbial heterotrophic activity
by tracing the fate of specific labelled substrates are inadequate. The main reason for their
inadequacy is due to the fact that they provide an indirect, although very sensitive,
measurement. A comprehensive review of those methods and of the problems involved in
their use was published by van Es and Meyer-Reil (1982). In order to evaluate directly the
flow of naturally occurring OC through the microbial heterotrophic population, the
heterotrophic consumption of the natural pool of OC in lake water was followed by
microanalytical methods. This approach is based on the assumption that modern OC
analyzers are sensitive enough to allow the direct measurement of heterotrophic OC
utilization under controlled conditions. As a necessary premise to this approach, the
analytical capabilities of the instruments used will be illustrated.
103
IFREMER, Actes de Colloques, 3, 1986, pp. 103-108
11
EVALUATION OF THE HETEROTROPHIC ACTIVITY IN WATERS BY MICROANALYTICAL METHODS
R. BERTONI
CNR - Istituto Italiano di Idrobiologia, Pallanza, (ITALY).
ABSTRACT - The radiochemical methods proposed for evaluating heterotrophic activity in waters have been
severely criticized in recent years because they are not considered to be sufficiently realistic. Thus, the possibility
of directly measuring the heterotrophic consumption of naturally occurring Organic Carbon (OC) in fresh water
samples incubated under controlled conditions has been evaluated. The analytical performances of two OC
analyzers utilizable for this purpose are discussed here, and some examples of the results obtained by the direct
measurement of OC consumption are presented. The consumption rates thus measured range from 11.6 to
50.2 µgC/ 1.h. Although the technique discussed here is less sensitive than radiochemical methods, the few
assumptions needed when making a direct measurement largely offset this loss of sensitivity.
Key words : heterotrophic activity, organic carbon cycle, organic microanalysis.
RÉSUMÉ - Les méthodes consistant à estimer l’activité hétérotrophe à partir de mesures d’incorporation de
substrats radioactifs ont été critiquées dans ces dernières années parce que insuffisamment proches de la réalité.
Pour obtenir une estimation plus représentative, on a essayé de mesurer directement la consommation
hétérotrophe du carbone organique naturellement présent dans les eaux sur des échantillons incubés en
conditions contrôlées. Les potentialités analytiques de deux instruments utilisables pour ce but sont ici illustrées
et des résultats obtenus par la mesure directe de la consommation hétérotrophe du carbone organique sont
présentés. Dans les lacs étudiés on a mesuré des vitesses de consommation du substrat naturel comprises entre
11.6 et 50.2 µg C/l.h. Bien que cette technique soit moins sensible que les méthodes radiochimiques, elle
n’implique pas des hypothèses difficiles à vérifier et cet avantage compense largement sa moindre sensibilité.
Mots clés : activité hétérotrophe, cycle du carbone organique, microanalyse organique.
INTRODUCTION
It is essential for those concerned with the heterotrophic processes within the Organic
Carbon (OC) cycle to know the total OC flow through the decomposer microheterotrophs. For this purpose the methods which evaluate the microbial heterotrophic activity
by tracing the fate of specific labelled substrates are inadequate. The main reason for their
inadequacy is due to the fact that they provide an indirect, although very sensitive,
measurement. A comprehensive review of those methods and of the problems involved in
their use was published by van Es and Meyer-Reil (1982). In order to evaluate directly the
flow of naturally occurring OC through the microbial heterotrophic population, the
heterotrophic consumption of the natural pool of OC in lake water was followed by
microanalytical methods. This approach is based on the assumption that modern OC
analyzers are sensitive enough to allow the direct measurement of heterotrophic OC
utilization under controlled conditions. As a necessary premise to this approach, the
analytical capabilities of the instruments used will be illustrated.
103