Gram stain index of a natural bacterial community at a nutrient gradient in the freshwater environment

Species succession of a natural bacterial community was indicated by the Gr am stain index (GSI) using an experimental nutrient gradient in an oligotro phic pond created with an in situ gradostat. Various trophic conditions, ra nging from eutrophic to mesotrophic, were formed experimentally with contin uous inflow of sterile peptone solution in the gradostat, while the water m ass outside the gradostat was oligotrophic. The GSI spectra of the natural bacterial populations show different profiles in accordance with the trophi c level of the ambient water and the time progression of adaptation to diff erent levels of eutrophication. Therefore, GSI can be used as a potential i ndicator of organic pollution in aquatic environments. (C) 2000 Elsevier Sc ience Ltd. All rights reserved.