ABSTRACT
A non-linear dependence of the inhibition of E. coli cells is found when irradiated simultaneously with the blue and red regions of the spectrum at a power density of 100 mW/cm2. Such dependence is explained by the assumption of a cascade two-photon absorption of light by DNA molecules with an intermediate resonance at cellular chromophores, causing excitation and subsequent DNA damage similar to damage when exposed to UV radiation.
Subject(s)
DNA Damage/radiation effects , Escherichia coli/radiation effects , Microbial Viability/radiation effects , Light , Ultraviolet RaysABSTRACT
Bacterial mats in sulfide aquatic systems of North Caucasus are basically composed by the species of genera Thiothrix and Sphaerotilus. Additionally, several non-filamentous sulfur-oxidizing bacteria were isolated from the mats and several minor 16S rRNA phylotypes were found in clone libraries from these mats. The minor components were affiliated with Proteobacteria, Chlorobia, Cyanobacteria and Firmicutes. Even in an individual mat population heterogeneity of Thiothrix spp. was revealed by analysis of 16S rRNA gene and RAPD-PCR. Five Thiothrix isolates were described as new species Thiothrix caldifontis sp. nov. and Thiothrix lacustris sp. nov. In the Thiothrix-Sphaerotilus type of bacterial mat the proportion of dominant organisms might be influenced by sulfide concentration in the spring water. The higher sulfide concentration (more than 10 mg/l) in the spring water is more favorable for the development of bacterial mats with dominant Thiothrix organisms than for Thiothrix-Sphaerotilus type of sulfur mat.
