EFFECT OF HETEROTROPHIC BACTERIA ON DIFFERENT HUMIC SUBSTANCES IN MIXED BATCH CULTURES

Abstract

Humic substances extracted from different soil samples and synthetic humic compounds (two melanoidins and one synthetic polymer) were used as the sole carbon source in liquid media inoculated with a mixed bacterial community selected by adaptation culture technique, and incubated for 90 or 100 d. The results show a high resistance to degradation of humic compounds by heterotrophic bacteria. Only a slight decrease in carbohydrate content and some modifications in carboxyl content were observed with the natural compounds. This resistance to biodegradation does not seem to be related to sample origin (e.g., forest humic substances compared to cultivated soil humic substances), or extraction procedure (sodium pyrophosphate compared to sodium hydroxide). Fulvic acids were as refractory as humic acids. The action of heterotrophic bacteria on incubated humic substances was similar under anaerobic (with nitrate reducing conditions) and aerobic conditions. Key words: Fulvic acids, humic acids, humus recalcitrance, melanoidins