Effect of tetracycline on the colonization and growth of microbes on Scirpus lacustris litter in oligotrophic and eutrophic waters

Abstract

Studies of microbes on Scirpus lacustris submerged in river (oligotrophic) and wetland (eutrophic) waters were conducted to determine how nutrient status affected colonization and growth on the same substrate. The antibiotic tetracycline was used to repress bacteria to determine if they inhibited fungal growth. The use of tetracycline was also relevant in a broader context as antibiotics are now being detected in aquatic systems. Dead S. lacustris stems were submerged for 33 d in natural and tetracycline amended (500 and 4000 µg l -1 ) river and wetland waters. Confocal laser scanning microscopy was used to scan the biofilm while image analysis was used to determine microbial (algal, bacterial, fungal) cell volume and fungal biomass by measuring the length of fungal hyphae. In all treatments, microbial cell volume peaked on Day 10 and was greater (ANOVA, all p 0.05). On Day 10, the controls of both water treatments had significantly greater microbial biovolume than both the 500 and 4000 µg l -1 antibiotic treatments (both p = 0.02), indi- cating that tetracycline had a negative effect on microbes colonizing Scirpus.