A facile technique for automatically counting odor-producing algae (Pseudanabaena sp.) in drinking water sources

Abstract

The frequent analysis of the 2-methylisoborneol (2-MIB)-generating algae Pseudanabaena sp. for predicting odor occurrence in drinking water sources is a major challenge for many drinking water utilities. This study aims to establish a facile method for automatically determining the counts of Pseudanabaena sp. in lake water by site workers without requiring analytical skills. The analytical technique is based on observations of auto-fluorescence emitted from chlorophyll. The auto-fluorescence intensity of cyanobacteria, including Pseudanabaena sp., was relatively weak and uniform throughout the cells, whereas other algae such as diatoms and green algae showed a highly variable auto-fluorescence intensity in their cells, which allowed us to discriminate cyanobacteria from all other algae. Among cyanobacteria, the length and width of Pseudanabaena sp. are unique; thus, the criteria for recognizing only Pseudanabaena sp. among algae were developed based on its dimensions and fluorescence intensity. The developed auto-counting method was successfully validated by attaining a high correlation between the manually and automatically recorded Pseudanabaena sp. counts in lake water samples. Although the developed method can overestimate the Pseudanabaena sp. counts due to the presence of other similar-sized microorganisms, frequent on-site analysis using this facile method will play a role in providing early warnings of potential 2-MIB occurrence and enabling precautionary countermeasures at drinking water treatment plants.