Quantitative Study of Saprophytic and Cellulose-Decomposing Microorganisms in Mountain Meadow, Soddy Meadow, Alluvial-Carbonate, and Meadow Brown Soils of Eastern Georgia

Abstract

Microorganisms play a particularly important role in the biological activity of soils, as they are responsible for the transformation of organic matter, humus formation, and minerals mobilization. Georgia is distinguished by exceptional soil diversity, and nearly all major soil types except tropical soils are represented within its territory. The aim of the present study was to investigate the microflora of different soil types of Eastern Georgia — mountain meadow, soddy mountain meadow, alluvial-carbonate, and meadow brown soils; in particular to study the content of saprophytic and among them cellulose-decomposing microorganisms in relation to soil type. The study employed widely accepted modern microbiological methods. Sampling was carried out using the Waksman’s envelope method. Microbial groups were studied using the dilution method. Meat-peptone agar (MPA) was used for cultivating saprophytic bacteria, while Imshenetsky-Solntseva’s and Czapek’s media were used for cellulose-decomposing microorganisms. The number of saprophytic bacteria was determined by the direct counting method, whereas cellulose-decomposing microorganisms were quantified using McCready’s table. For microorganisms identification were studied: structural features of colonies (shape, size, spore formation, motility, colony morphology); nutritional characteristics; utilization and transformation of chemical compounds; metabolic products; response to oxygen, temperature, and acidity; and genetic characteristics. In all soil types, saprophytic bacteria belonged to the genus Bacillus, while cellulose-decomposing bacteria belonged to the genus Cellulomonas. Three genera of cellulose-decomposing fungi were identified in the soils: Aspergillus, Penicillium, and Fusarium. The maximum total number of microorganisms was observed in alluvial-carbonate soil. Mountain meadow and meadow brown soils were distinguished by greater morphological diversity of microorganisms. The largest number of saprophytic bacteria was recorded in alluvial-carbonate soil. Cellulose-decomposing microorganisms dominated in meadow brown soil. The obtained results indicate that the studied soils of Eastern Georgia are characterized by high microbial activity and a well-developed cellulose-decomposing microflora. Near-neutral pH, moderate moisture, and the presence of organic matter create favorable conditions for the functioning of both bacteria and fungi, which play an important role in organic matter mineralization and biogeochemical cycles in soils.