*2.1. Growth Response to ZnCl2 in M. Aeruginosa UTEX LB 2385*

To better evaluate the zinc metal resistance and response mechanisms of a globally important toxigenic cyanobacteria species, *M. aeruginosa* UTEX LB 2385 cultures were used for the observation of physiological responses to long-term ZnCl2 concentrations exposure via growth monitoring (Figure 1). For *M. aeruginosa*—UTEX LB 2385 cells exposed to 0.1 mg/L ZnCl2, the cell concentration was similar to 0 mg/L ZnCl2 (control) through 15 days (Figure 1). However, the average turbidity for *M. aeruginosa* UTEX LB 2385 culture cells exposed to all ZnCl2 concentrations decreased below the initial control measurement (optical density, OD750 nm ≈ 0.47) for 0.1, 0.25, and 0.5 mg/L ZnCl2 by Day 1 (Figure 1b). When compared to control cells, *M. aeruginosa* UTEX LB 2385 culture cell numbers exposed to 0.25 mg/L ZnCl2 were reduced by ~28% by Day 15 ((4.73 ± 1.243/8.41 ± 0.122) × 100) (Figure 1a). At the highest concentration treatment (0.5 mg/L ZnCl2), *M. aeruginosa* UTEX LB 2385 culture cells were almost completely inhibited in comparison to 0.25 mg/L ZnCl2 cells by the end of the growth monitoring period. This concentration (0.5 mg/L ZnCl2) may therefore present as the ZnCl2 minimum inhibitory concentration (MIC) for *M. aeruginosa* UTEX LB 2385 within this study (Figure 1). Aside from these observations, *M. aeruginosa* UTEX LB 2385 culture cells treated with 0.25 and 0.5 mg/L ZnCl2 were observed via hemocytometer to possess larger aggregate cell clusters and extracellular debris compared to control cells.
