The impact of UV mediated hydrogen peroxide on culturable bacteria in the surface microlayer of eutrophic lake

Hydrogen peroxide (H₂O₂) formation in surface waters is initiated by the absorption of sunlight by dissolved organic matter (DOM). The fraction of the DOM pool that interacts with sunlight, referred to as chromophoric dissolved organic matter, impacts the optical properties of surface waters. Second source of H₂O₂ is wet and dry deposition of photogenerated substance in the atmosphere and biological production. The study examined the concentration of hydrogen peroxide in water from the surface microlayer (SM) (<100 m) and subsurface water (SSW) (25 cm) in the typical eutrophic (TOC 5–15 mg dm⁻³; chlorophyll 5–26 g dm⁻³, water transparency 0.6–1.0 m) lake as well as the impact of this compound on occurrence and survivorship of catalase-positive and catalase-negative bacteria isolated and cultured on the TSA medium (Difco). The experimental H₂O₂ concentrations ranged between 500–5000 nM. The concentration of H₂O₂ in analyzed water samples clearly increased in day-time hours and was different in May, July and October. The highest natural concentration of H₂O₂ (700 nM) was observed in SM water in summer in afternoon hours. During that period, 100% of bacterial populations found in SM water produced catalase. The experiments confirmed that environmental concentrations of H₂O₂ caused no considerable decrease in survivorship of culturable bacteria, while concentrations exceeding 1000 nM were lethal for the majority of catalasenegative bacteria, but not for catalase-positive bacteria.