Comparison of detachment procedures for direct counts of bacteria associated with sediment particles, plant litter and epiphytic biofilms

Efficient detachment of bacterial cells is crucial for assessing bacterial abundance, biomass and community composition in natural and technical systems (e.g. sewage plants) by a wide range of analytical methods. There is no agreement on which procedure gives the best results with which type of substratum. We tested the effect of 4 detachment instruments on the release of bacteria associated with leaf litter, sediment and epiphytic biofilms from a natural aquatic system. Treatment with most instruments increased bacterial counts and biovolumes significantly compared to simple vortexing (by 2.7 to 7x). However, both the numbers and biovolume of released bacterial cells varied significantly between detachment devices. With leaf litter and epiphytic biofilms, an ultrasonic probe treatment released 10 and 4 times more bacterial cells than the most inefficient instrument. A stomacher-type blender gave the best results for sediment samples, releasing 3 times higher numbers of bacteria than the least efficient instrument. Neither the detachment instrument nor the treatment time affected the composition of bacterial morphotypes. These results indicate that the choice of the appropriate detachment device depends critically on the type of substratum examined, when the absolute abundance or biomass of bacteria is to be determined. In qualitative analyses of bacterial community structure the chosen device appears to be less important.