Vol 88, No 1 (2019)

The review presents the results of investigation of the interaction between the hydrophobic substrate hexadecane and microbial cells. Three aspects of this process are discussed in more detail: (1) interaction of bacterial cells with the hydrophobic substrate, including characteristics of the cell surface and the conformational changes occurring at contact between the cell and the insoluble substrate; (2) molecular basics of the degradation of hydrophobic compounds at each stage of the cell–substrate interaction, such as synthesis of dispersing components, dispersion of the water-insoluble substrate, sorption of the hydrophobic compound by the cell and its storage, as well as transcription regulation of the genes involved either directly in biodegradation or in the processes associated with growth on hydrophobic substrates; and (3) bacterial synthesis of surfactants in the course of the degradation of hydrophobic compounds, diversity of their structure and conditions for their enhance release, as well as their biotechnological application.

Taking into account the accepted concept of the ancient whole genome duplication (WGD) in the yeast genus Saccharomyces, comparative analysis of the multiple α-glucosidases MAL and IMA of the genetic line Saccharomyces cerevisiae S288C and α-glucosidases of protoploid yeasts Kluyveromyces and Lachancea, which have not experienced genome duplication, was carried out. Only certain MAL and IMA isoforms of the latter two genera were shown to be in a close phylogenetic relationship to α-glucosidases MAL12, MAL32, and IMA1-IMA4 of S. cerevisiae S288C, while others were closer to the divergent IMA5. These results are consistent with the WGD concept, according to which the yeast Saccharomyces, Kluyveromyces, and Lachancea originated from the common protoploid ancestor and may therefore have common closely related α-glucosidases MAL and IMA. The identity of amino acid sequences of the IMA1-IMA4 isomaltoses of S. cerevisiae S288C to those of L. dasiensis, L. fantastica, L. fermentati, L. lanzarotensis, L. meyersii, L. quebecensis, and L. thermotolerans was 75−100%, while identity of the MAL maltoses of the same species was 75−99%. Importantly, the MAL and IMA α-glucosidases diverged independently in each genus, species, and even strain.

In order to investigate the effect of the RapA1 protein on growth-stimulating activity, biofilm formation, and root colonization by rhizobia, strains Rhizobium leguminosarum Pvu5, VSy12, Thy2, TPr4 and R. galegae 0702 were transformed with the pJN105TurboRapA1GFP vector, providing for constitutive expression of the rapA1 and gfp genes. Constitutive expression of the rapA1 gene was shown to result in more efficient biofilm formation on inert surfaces and to promote microcolony formation on plant root surfaces. Analysis of auxin production by wild and transformed strains revealed decreased auxin synthesis in all transformed strains, except for R. leguminosarum Thy2. Growth-stimulating activity of the wild and transformed strains did not correlate with the amount of auxins produced in vitro.

Effect of low-frequency pulsed magnetic field and of low-intensity laser radiation on mycelial fungi actively degrading various polymer materials was studied. These factors had a different effect on spores of fungi and mycelia. Irradiation could stimulate and suppress fungal growth. The studied physical factors had dose-dependent effects on activity of the extracellular fungal oxidoreductases (catalase and peroxidase); both increased and decreased enzymatic activities were observed.

Present study was carried out to isolate the effective bacterial strains for the degradation of petroleum hydrocarbons and biosurfactant production. The bacterial strains were screened for production of biosurfactant by CTAB methylene blue agar assay, hemolytic activity assay and drop collapse assay. The selected strain was identified as Corynebacterium species by 16S rRNA sequence analysis. Biosurfactant was characterized using thin layer chromatographic analysis revealed that the biosurfactant may be glycolipids which have different functional groups viz: alkenes, carboxylic acids and aliphatic amines. GC-MS analysis confirmed that the biosurfactant was 13-docosenamide (z). Biosurfactant also induces the growth of petroleum degrading bacteria i.e. Corynebacterium species. The results proved that the maximum growth was found at 96 h with biosurfactant (13-docosenamide (z)) and 144 h without biosurfactant. The study reflected the potential use of this biosurfactant for petroleum degradation and its application for in situ bioremediation of petroleum hydrocarbons contaminated sites.

The community of anoxygenic phototrophic bacteria (APB) from the water column of the meromictic Lake Trekhtsvetnoe (Kandalaksha Bay, White Sea, Russia) was studied in March 2012 and 2013 and in September 2013 and 2014. The community structure below the chemocline was shown to restore during three years after partial mixing resulting from seawater admixture into the lake in autumn 2011; a dense layer (at least 10⁸ cells mL^–1) of green-colored (g/c) sulfur bacteria (GSB) was formed. During winter, development of low numbers of brown colored (b/c) GSB was observed in the upper layer of green water. During summer seasons, b/c GSB were found to be located in the oxic zone above the green water layer, which was unusual for these organisms. The APB community was found to contain purple bacteria. Four APB strains were isolated from the upper part of the sulfide zone. The b/c and g/c GSB strains were phylogenetically close to each other and to the type species Chlorobium phaeovibrioides DSM 265 (99% similarity gene sequences). One strain of purple bacteria was phylogenetically related to the brackish sulfur bacteria Thiocapsa marina, while the other was related to freshwater bacteria Rhodopseudomonas palustris. The strains of sulfur bacteria were phylogenetically close to the chemocline bacteria from the stratified Lake Kislo-Sladkoe, also located in the coastal zone of the Kandalaksha Bay, White Sea.