Original paper

Ecophysiological status of bacteria in freshwater lakes during steep summer stratification

Tammert, Helen; Ott, Ingmar; Kisand, Veljo

Abstract

Bacterioplankton as a whole comprises a variety of individual cells ranging in physiological status from dead to highly active. Insight into the physiological status of bulk bacterioplankton allows the functional role of bacteria in a particular environment to be better understood. In the present study, three sharply stratified freshwater lakes were studied because such lakes provide a wide variety of ecological niches in a relatively small scale. Water samples were taken from the major layers of the water column and the total number and productivity of bacteria were measured. Two staining methods were used to determine the abundance of cells with respiratory activity and cell membrane integrity. The proportions of dead, intact and respiring bacteria were highly variable. The highest percentage of dead cells observed was close to 90%, while the highest proportion of respiring bacteria was 31%. Assuming that only respiring bacteria were responsible for bacterial production, the observed generation times ranged from 7 h to 30 days. When all cells (total number of bacteria) were assumed to grow actively, the calculated generation time increased to 2 years. The relationship between biomass and production indicated that respiring bacteria had lower growth efficiency in a shallow lake with high primary production; growth efficiency was higher in a deep lake with lower primary production.

Keywords

bacterioplanktonactivedormant and dead cellsgrowth rate