Effect of different heterotrophic plate count methods on the composition of culturable microbial community

Heterotrophic plate counts (HPC) are routinely determined within the scope of water qualityassessment. However, variable HPC methods with different cultivation conditions are applied.These variabilities can have a significant effect on the outcome of the analysis, particularly withregard to the composition of culturable microbial community. This was demonstrated by testingcommonly used low and high incubation temperatures (22 and 37°C) as well as high and lownutrient media (yeast extract agar and R2A). The culturable microbial community composition wasinvestigated by 16S rRNA gene sequencing and additional statistical analysis (ANOVA permutationtest on CCA and PERMANOVA). Lower temperature(22°C) showed the abundance of naturallyoccurring Pseudomonadaceae and Aeromonadaceae, whereas at high temperature (37°C)numerous Enterobacteriaceae and Bacilli were identified. The highest biodiversity was detected atlower temperature, especially on R2A medium. The most significant effect of tested cultivationconditions was assigned to temperature (p certain detected bacteria (as seen in the number of operational taxonomic units). These resultsendorse the supposition that different temperatures (low and high) should be included into HPCmeasurement, whereas the selection of media should take into account the monitored watersource itself. Accordingly it can be inferred that the HPC method is more suitable for continuousmonitoring of water quality than for single assessments.