Production of gaseous hydrocarbons by the microbial community of the Posolsky Bank methane seep bottom sediments (southern Baikal) was studied at 4°C. Formation of both methane and a heavier gaseous...

Under natural conditions, biodegradation processes proceed slowly, especially in regions with low temperature. To activate vital processes in hydrocarbon-oxidizing microorganisms at low temperatures, biologically active compounds can be employed as growth stimulants. A low-temperature (10 °C) study has shown that tris-(2 hydroxyethyl) ammonium arylchalcogenylacetates, "protatranes" exert an effect on the growth of hydrocarbon-oxidizing strains of Rhodococcus erythropolis and Pseudomonas fluorescens, isolated from natural oil seepage on Lake Baikal. It has been found that "protatranes", at microconcentrations, increase the growth rate of R. erythropolis bacteria by 2-16 times. It has been established that compounds slightly effect the growth of P. fluorescens. The positive effect of "protatranes" compounds on the growth rate of hydrocarbon-oxidizing microorganisms at low positive temperatures can be used for the development of environmentally benign methods for the restoration of natural objects after their contamination with oil.

The microbial community in the area of oil seep in Mid-Baikal (Cape Gorevoi Utes) was studied. The number of microorganisms that oxidize normal hydrocarbons, petroleum, and easily accessible organic matter in the water mass of the lake, bottom sediments, and bitumen structures was studied in 2005–2009. The high heterogeneity of the distribution of microorganisms associated with the deparaffination of oil in the areas of oil seeps was noted. The maximum concentrations of hydrocarbon-oxidizing microorganisms in the samples of bottom water above bitumen structures (up to 2200 ± 175 CFU/mL) and in bitumen structures themselves (up to 170 000 ± 13 000 CFU/g) were determined. A model experiment showed that in the conditions of low temperatures (4°C) the degradation of the fraction of oil n-alkanes by the natural microbial community reaches 90% over a period of 60 days.

This paper performs a detailed study of a wide set of organic-geochemical proxies in 15 sediment cores collected from the main basins of Lake Baikal (the northern, the central and the southern) where processes of focused fluid discharge were detected. A variety of studied zones includes sites with gas and hydrothermal seepage, mud volcanoes with or without gas-oil fluid discharge, gas hydrates and authigenic carbonates. The composition of the dispersed organic matter and individual hydrocarbon molecular markers (n-alkanes, dimethyl alkanes, isoprenoids, steranes, terpanes and polycyclic aromatic hydrocarbons) testify to the input from predominantly allochthonous terrestrial and autochthonous microbial and algal sources. The studied sources, maturity and biodegradation parameters of organic matter vary significantly for areas with different fluid discharge. The composition of specific biomarkers including isoprenoids and immature hopanoids reflects the lateral and vertical changes of microbial activity in sediments associated with various environmental conditions. The identified types of terpanes distribution (mature, mixed and immature) correlate well with types of fluid discharge and attest to the development of various methanogenic and methanotrophic microbial communities in sediments. Moreover, the revealed specificity of microbial molecular markers distribution allowed us to suggest the fluid discharge processes in zones where they were not previously detected.