EFFECT OF SELECTED ANTIBIOTICS ON THE GROWTH AND MORPHOLOGY OF CYANOBACTERIA

Antibiotics in the environment represent a significant pollutant with a great impact on the biota. With the increasing use of these substances, the resistance against them notably grows. The phototrophs, as the key part of microbial communities, often have different responses to antibiotics. Some species could be inhibited; on the other hand, some species show the ability to use antibiotics as a source of necessary nutrients. In our study, we investigated the impact of streptomycin, gentamicin, and sulfacetamide on six strains of cyanobacteria commonly present in water sources. The growth inhibitory effect of the studied antibiotics was measured in sterile 96-well microtiter plates, which contained different concentrations of antibiotics (1024 – 0.5 µg/mL) during 7 days at 23 °C and with 24h illumination (light intensity 48,6 µmol. foton m-2 s-1).  Then the results were statistically evaluated, and growth curves were designed for each studied strain. The minimum inhibitory concentration (MIC) of the investigated antibiotics was evaluated using probit analysis. The potential effect of antibiotics on tested strains morphology was also studied.  The results show that the antibiotics have an inhibitory effect at higher concentrations (891.76 μg/mL to 1495.10 μg/mL). The highest values of MIC were estimated for Synechocystis sp. (PCC 6803) and Cephalotrix sp. (KL 18). The stimulation of growth was observed in the strains Synechocystis (PCC 6803) and Cephalothrix (KL 18). The most sensitive strains to selected antibiotics were Chlorogleopsis fritschii (CCALA 1005), Lyngbya martensiana (CCALA 930), and Geitlerinema acuminatum (CCALA 141). Strain Cyanobium sp. (LH14) was sensitive to streptomycin sulphate and gentamicin sulphate, but sulfacetamide stimulated its growth. The visible morphological changes were caused by streptomycin in Chlorogloeopsis fritschii (CCALA 1005). After five days of cultivation the bleached cells were present in the cultures of this strain.