卷 52, 编号 10 (2018)

The cold-water Volkhov and warm-water Keila hardgrounds of the Ordovician Baltic Basin represent a specialized product of cyanobacterial communities of the seafloor, another member in a group containing stromatolites and microbially induced sedimentary structures. The leading role of cyanobacterial communities in the development of hardgrounds is suggested by their macrofeatures, structure, and elemental composition revealed by SEM equipped with a microprobe microanalyzer. During the formation of the hardgrounds, the cyanobacterial films were of considerable thickness (up to 4–5 mm), but lacked vertical zonation of bacterial communities, thereby being at an intermediate stage between the mature biofilms and true mats. The soft substrate underlying hardgrounds was inhabited by an abundant infauna. Thanks to bioturbation, the cyanobacterial film was in places destroyed, which prevented the development of hardgrounds. In the warm Late Ordovician basin of northern Estonia, cyanobacterial films formed hardgrounds on the surface of ripple marks. Abundant peloids and warm pore waters facilitated further cementation and hardening of the substrate underneath the hardground before the burial of the ripple marks and the hardground. Cyanobacterial films appeared simultaneously over large areas of the seafloor due to settling of planktonic bacteria. The extracellular polymeric substances (EPSs) released by these bacteria were rapidly mineralized within a maximum of one season, apparently at a depth of 15–25 m, below the fair weather wave base. The formation of hardgrounds in bioherms occurred in a shallower environment and was patchy due to the alternation of living and dead cyanobacterial mats, mineralizing mats and resulting hardgrounds. Inhabitants of biohermal hardgrounds were producers of carbonate detritus, including of micritic size, over vast areas of the seafloor surrounding the bioherm.

The leading role of bacterial communities in the formation of marine sedimentary rocks is inferred from the synthesis of expert knowledge about bacterial paleontology, while the results of oceanic studies (materials and data) offer new insights into symbiotic relationships between phototrophic and chemotrophic bacteria and fauna.

Precambrian cyanobacteria demonstrate unprecedented evolutionary conservatism and have remained practically unchanged for the last 2 Ga, considering that ancient forms have counterparts among genera and even species of modern microorganisms. However, Proterozoic cyanobacteria and other prokaryotes form unique assemblages of restricted geochronological range and broad spatial distribution. The most remarkable of these assemblages are the Gunflint-type Paleoproterozoic microbiotas and the Early Riphean Archaeoellipsoides-dominant Kotuikan-type assemblages. Their observed taxonomic uniqueness and short geochronological ranges reflect irreversible changes in the Earth’s global environments, rather than evolutionary innovations. Nonetheless, the fossil blue-green algae demonstrate some evolutionary changes throughout the Proterozoic: the stalked cyanobacteria Polybessurus appeared in the Middle Riphean and the spiral cylindrical cyanobacteria Obruchevella emerged in the Late Riphean.

Microstructures of silicic rocks shaped by the activity of thermophilic bacterial communities in active volcanism areas of Kamchatka are described in the present article. The role of microorganisms as a special matrix that accelerates the formation of microlayered rocks of mixed chemogenic and biogenic origin is demonstrated. The authors suggest the term “biosilicites” for such rocks.

Results of an integrated study of microbial communities in soils and soil-like bodies formed in the wet intermountain valleys of East Antarctic oases under moss-, lichen-, algae- or cyanobacteria-dominated associations are summarized. Colonization of soil horizons by microorganisms, microbial biomass, potential biological activity, high viability of soil microorganisms and their resistance to extreme environmental conditions are considered. Perspectives of microbiological studies addressed towards evaluation of the functional role of microorganisms in the formation of Antarctica soils are discussed.

Ionizing radiation is among the most important planetary factors that regulate the intensity and dynamics of biospheric processes. At the early stages of life on the Earth, short-wave radiation permeated the Earth surface. The evolution of the planet, corrected by fluctuations of cosmophysical factors, contributed to the development of the adaptation processes in the emerging biosystems, including resistance to a wide range of ionizing effects. Studies of microorganisms from extreme habitats have changed the scientific paradigm of cell viability and adaptive potential. The taxonomic spectrum of bacteria and archaea, isolated from extreme biotopes and resistant to ionizing radiation, is constantly enlarged. However, it is also necessary to develop in situ studies at the system level, as well as to assess the ecosystem stability and prospects for its restoration as the basic unit of the biosphere during prolonged exposure to radiation and accumulation of significant doses. The goal of this research was to study the effects of high doses (60‒250 kGy) of ionizing gamma radiation on the viability of bacterial communities in frozen sedimentary rocks and modern soils, as well as to assess the aftereffect of high doses on natural samples.