Impact of humic substances on bacterioplankton in eutrophic lake

This paper presents the results of resarch on impact of humic substances (HS) on bacterioplancton in eutrophic Lake Jeziorak (north-eastern Poland). In cultures of natural bacteria from the lake water, enriched with 0, 5, 10, 25 and 50 mg dm⁻³ of HS (natural HS – isolated from lake water or commercial HS – sodium salt of humic substance; Sigma-Aldrich), were determined the following parameters: total number of bacteria (TNB), number of heterotrophic bacteria (CFU), bacterial production (BP) (measured with [³H]methyl thymidine method) and general activity of esterases. Natural HS had a more positive impact on bacterial growth, bacterial production and activity of esterases than the commercial preparation HS. The highest TNB and CFU was observed when the water was enriched with 25 mg dm⁻³ of natural HS. All concentrations of the natural HS stimulated bacterial production. The activity of hydrolytic enzymes increased with rising concentrations of natural HS.