The number, structure, and physical state of the microbial communities in high-moor and low-moor peat bogs were compared. Distinct differences in these characteristics were revealed. The microbial biomass in the high-moor peat exceeded that in the low-moor peat by 2–9 times. Fungi predominated in the high-moor peat, whereas bacteria were the dominant microorganisms in the low-moor peat. The micromycetal complexes of the high-moor peat were characterized by a high portion of dark-colored representatives; the complexes of the low-moor peat were dominated by fast-growing fungi. The species of the Penicillum genus were dominant in the high-moor peat; the species of Trichoderma were abundant in the low-moor peat. In the former, the bacteria were distinguished as minor components; in the latter, they predominated in the saprotrophic bacterial complex. In the high-moor peat, the microorganisms were represented by bacilli, while, in the low-moor peat, by cytophages, myxobacteria, and actinobacteria. The different physiological states of the bacteria in the studied objects reflecting the duration of the lag phase and the readiness of the metabolic system to consume different substrates were demonstrated for the first time. The relationships between the trophic characteristics of bacterial habitats and the capacity of the bacteria to consume substrates were established.

This review presents an analysis of the results of mycological investigations of peat obtained by the authors and other Russian and foreign scientists. High-moor peat, unlike low-moor peat, is shown to contain great reserves of fungal biomass mainly represented by mycelium. The viability of the mycelium and spores is high in the upper peat horizons and does not exceed 50% in the lower ones. In high-moor peat, fungi that are capable of destroying the complex structural polymers composing up to 50% of the peat rarely occur. The analysis of the factors limiting the activity of fungi in the high-moor peatbogs showed that, in the upper layers, the main factor was the strength of the sphagnum cellular walls. In the lower layers, the significant oxygen deficit and the accumulation of sphagnans, sphagnols, phenol-containing compounds, and antioxidants that block the activity of hydrolytic and oxidizing enzymes are of great importance.

The population density and taxonomic structure of micromycetes were monitored for six months in a model experiment with natural and mechanically fragmented (fine and coarse) samples of sphagnum. Sphagnum fragmentation favored an increase in the number of micromycetes only during the first week of the experiment. On the average, the number of micromycetes in fine-fragmented samples was two times greater than that in the coarse-fragmented samples. The diversity of micromycetes increased in the fragmented samples of sphagnum owing to the activation of some species, which remained in the inactive state as spores in the peat before fragmentation.

Activity of extracellular enzymes was assessed in 20 strains of microscopic fungi involved in biodegradation of technical objects exploited under tropical climate conditions (Vietnam). It was found that 19 strains possessed catalase activity, 18 strains had phenol oxidase activity, and eight strains had protease activity. The effect of industrial biocides on the activity of these enzymes was also assessed. The biocides Bior-1, Bioneutral A 10, and Bioneutral A 101 were shown to inhibit the enzymatic activity to various extent. All biocides inhibited extracellular catalase activity in most fungal strains studied. The inhibition of protease and phenol oxidase activity of same test strains was less pronounced. The response to biocides varied at the strain level; its characteristics could differ significantly even between strains of the same species. In several cases, it was observed that exposure to biocides resulted in an increase in enzyme activity.

With high-throughput sequencing of the variable region V3–V4 of the 16S rRNA gene, the study of the full phylogenetic composition of microbial communities developed on the surface of titanium plates exposed in the water column of the coastal zone of the Black and White Seas was carried out. The presence of potentially corrosive microorganisms from various physiological groups, such as sulfate-reducing bacteria, acidophilic iron-oxidizing bacteria and archaea, sulfur-oxidizing and nitrifying bacteria, was shown in the fouling. In the fouling of titanium plates exposed in the Black Sea, the most common microorganisms were uncultivated sulfate-reducing bacteria of the order Desulfotomaculales, which accounted for 8.13% of all 16S rRNA gene sequence reads, as well as acidophilic iron-oxidizing bacteria of the genera Acidiferrobacter (5.47%), Acidithiobacillus (4.52%), and Acidiphilium (2.55%). Acidophilic archaea accounted for up to 7.97% of all reads. In the fouling of titanium plates exposed in the White Sea, the most common were also acidophilic bacteria from the orders Acidiferrobacterales and Acidithiobacillales (7.68%), as well as acidophilic archaea from the order Thermoplasmatales (7.43%). Uncultivated sulfate-reducing bacteria of the order Desulfotomaculales were also represented in relatively high numbers (6.61% of all reads).