Different interactions of phycoerythrin- and phycocyanin-rich Synechococcus spp. with diazotrophic bacteria from the picoplankton of Lake Constance
Postius, Christine; Böger, Peter
Archiv für Hydrobiologie Volume 141 Number 2 (1998), p. 181 - 194
published: Feb 19, 1998
ArtNo. ESP141014102009, Price: 29.00 €
The picoplankton (PP) from the pelagic zone of Lake Constance comprises photoautotrophic picocyanobacteria of the Synechococcus type and heterotrophs including nitrogen-fixing purple bacteria. Phycocyanin (PC)-rich and phycoerythrin (PE)-rich Synechococcus spp. isolated from this ecosystem responded differently to N-deprivation. The PC-rich strains BO8801, BO8805 and BO8806 exhibited a rapid decrease of phycobiliprotein to chlorophyll-a ratio. Concomittantly, an accumulation of cellular carbohydrates as well as enhanced concentrations of released extracellular polysaccharides were observed. Addition of the concentrated cell-free culture medium from the N-deprived PC-rich strain BO8806 increased the light-induced nitrogenase activity of picoplankton fractions enriched in heterotrophic bacteria including diazotrophic ones from the pelagic zone (HPP). In contrast, the PE-rich strains BO8807, BO8808 and BO8809 did not respond to N-deprivation in pigment composition and no significant accumulation of polysaccharides was observed. Accordingly, no support of bacterial light-induced nitrogenase activity was found when concentrated culture medium of the N-deprived PE-rich isolate B08807 was applied. This indicates that, different from the PE-rich isolates, the PC-rich strains released compounds which were metabolized by diazotrophic phototrophs present in the HPP. Weekly examination during one year of picoplankton fractions of Lake Constance for the capability to reduce acetylene revealed the occurrence of an enhanced lightinduced nitrogenase activity profile concurrent with the spring bloom of picocyanobacteria. These findings suggest that PC-rich picocyanobacteria may contribute to the C-supply of diazotrophic bacteria in the natural environment.