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 quality<br>assessment. However, variable HPC methods with different cultivation conditions are applied.<br>These variabilities can have a significant effect on the outcome of the analysis, particularly with<br>regard to the composition of culturable microbial community. This was demonstrated by testing<br>commonly used low and high incubation temperatures (22 and 37°C) as well as high and low<br>nutrient media (yeast extract agar and R2A). The culturable microbial community composition was<br>investigated by 16S rRNA gene sequencing and additional statistical analysis (ANOVA permutation<br>test on CCA and PERMANOVA). Lower temperature(22°C) showed the abundance of naturally<br>occurring Pseudomonadaceae and Aeromonadaceae, whereas at high temperature (37°C)<br>numerous Enterobacteriaceae and Bacilli were identified. The highest biodiversity was detected at<br>lower temperature, especially on R2A medium. The most significant effect of tested cultivation<br>conditions was assigned to temperature (p &lt; 0.01), although media also affected the abundance of<br>certain detected bacteria (as seen in the number of operational taxonomic units). These results<br>endorse the supposition that different temperatures (low and high) should be included into HPC<br>measurement, whereas the selection of media should take into account the monitored water<br>source itself. Accordingly it can be inferred that the HPC method is more suitable for continuous<br>monitoring of water quality than for single assessments.