Ecophysiological performance of an urban strain of the aeroterrestrial green alga Klebsormidium sp (Klebsormidiales, Klebsormidiophyceae)

Aeroterrestrial green algae are among the most ubiquitous members of the microbial flora colonizing aerial surfaces. Filamentous green algae, in particular, produce large populations in several natural and artificial habitats. In recent years it has been shown that the bases of the walls of urban environments are frequently colonized by filamentous green algae. However, information concerning the physiology of these organisms and the factors that determine their distribution is extremely limited. We studied the physiological responses of a strain of Klebsormidium sp. (Klebsormidiales, Klebsormidiophyceae) collected in an urban area (Konstanz, Germany). Growth responses, photosynthetic performance, desiccation tolerance and accumulation of organic osmolytes were measured in several different combinations of environmental factors. Klebsormidium sp. exhibited optimal growth and highest photosynthetic efficiency under relatively low photon fluence rates, performing optimally between 15 and 30 mu mol photons m(-2)s(-1) and showing increasing inhibition above 85 mu mol photons m(-2)s(-1). Although it could survive at salinities up to 60 psu, this alga was relatively stenohaline; growth was optimal between 1.2 and 15 psu and declined considerably at higher salinities. Sucrose acted as the major organic osmolyte, and its concentration increased almost linearly between 1.2 and 30 psu from 29.7 to 171.2 mu mol g(-1) dry weight. Further increases in salinity, however, were accompanied by a strong reduction in sucrose content pointing to insufficient osmotic adjustment. Klebsormidium sp. was able to photosynthesize efficiently for up to 2 hours under complete desiccation. Afterwards, however, there was no measurable photosynthetic activity although complete photosynthetic efficiency (F-v/F-m) was recovered upon rehydration for 48 hours. Overall, the results correlate well with the ecology of Klebsormidium sp. in the field and its distribution in continental Europe.