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AME 23:213-224 (2001)
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Abstract
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Metabolically active bacteria in Lake Kinneret
T. Berman1,*, B. Kaplan1, S. Chava1, Y. Viner1, B. F. Sherr2, E. B. Sherr2
1Israel Oceanographic and Limnological Research, The Yigal Allon Kinneret Limnological Laboratory, PO Box 345, Tiberias 14 102, Israel
2College of Oceanic and Atmospheric Sciences, Oregon State University, Corvallis, Oregon 97330-5503, USA
*E-mail: tberman@ocean.org.il
ABSTRACT: Three staining methods were used to identify metabolically active bacteria in Lake Kinneret, northern Israel: CTC, DAPI staining followed by a propanol wash, and the Molecular Probes Live/Dead stain. Positive results from these methods purport
to show, respectively, actively respiring bacteria (CTC+), cells with intact nucleoids (NuCC), and cells with intact membranes (MEM+). Concomitantly, bacterial metabolic activity was measured as electron transport system (ETS) flux, O2 uptake,
activities of peptidase, b-glucosidase and lipase, and rate of leucine incorporation in monthly samples taken for 2.5 yr at a pelagic lake station. Laboratory experiments followed changes during 22 or 40 h in the percentages of
'active' bacteria in GF/C-filtered lake water with or without substrate enrichment or antibiotic inhibitors of cell division, or with bacterivorous protists. In lake samples, each of the staining methods detected different aspects of cellular state or
metabolic activity but all 3 indicated low percentages of 'active' bacteria relative to total bacterial abundance. CTC+ ranged from 1.0 to 27.3% (average 5.1%), NuCC from 1.4 to 42.9% (average 8.3%) and MEM+ from 1.0 to 29.9% (average 8.8%), with no clear
seasonal or spatial patterns. No significant correlations were found between the proportions of 'active' bacteria in lake water as determined by these methods, although such correlations were observed in the laboratory experiments. Significant
correlations were obtained between ETS and O2 uptake, peptidase and b-glucosidase, and between leucine incorporation and peptidase. ETS was significantly correlated with CTC+ and NuCC cell abundance, but not with
total bacteria (DAPI counts). In contrast, peptidase activity correlated with total bacterial counts. Results of time course experiments indicated that some bacteria which initially appear to be inactive can become active when stimulated by substrate
addition, even though cell division is inhibited. Grazing by protists increased the percentage of active bacteria, at least during the active predator-prey phase. Our data support the hypothesis that in natural waters usually only a small fraction
(probably <20%) of the entire bacterial assemblage is strongly active metabolically at any given time. This proportion may increase dramatically with localized substrate inputs. The concept of bacterial assemblages, heterogeneous not only in terms of
phylotype, but also in terms of levels of metabolic activity will need to be considered in future aquatic ecosystem models.
KEY WORDS: Metabolically active bacteria · Respiration · Hydrolytic enzymes · Lake Kinneret
Full text in pdf format
Published in AME Vol.
23, No. 3
(2001) on February 28
ISSN: 0948-3055.
Copyright © Inter-Research, Oldendorf/Luhe, 2001
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