Microbiology of sediments in lakes of differing degrees of eutrophication
A general survey was carried out on the sediments of seventeen lakes, ranging from oligotrophic to eutrophic, in the English Lake District. Several variables not directly concerned with the population of bacteria were measured to provide background information. Estimates of the total population of bacteria and of the population of filamentous bacteria were made using direct counts with acridine orange and fluorescein di-acetate, and counts by an MPN technique. The counts with acridine orange showed an upward trend with increasing degree of enrichment of the lakes, particularly at the eutrophic end of the spectrum. The distribution pattern obtained with the fluorochrome fluorescein di-acetate was different with an apparent upward trend in the intermediate lakes. The viable counts of the bacterial population in the sediments did not agree with the ranking of the lakes according to published information from the Freshwater Biological Association, although a slight upward trend was observed in the distribution of the viable filamentous bacteria. The preliminary survey led to the selection of three lakes representing the oligrotrophic, mesotrophic and eutrophic states in which a more detailed investigation on the population of filamentous bacteria was made. The profundal and littoral zones of the three lakes were investigated particularly in relation to the different groups of filamentous bacteria and their vertical distribution in the sediments. The groups of filamentous bacteria were described based on morphological and cytochemical tests. A tentative key for identification of filamentous bacteria was devised.