Double-stranded RNA viruses in a mycocinogenic strain of Cystofilobasidium infirmominiatum

The viral particles (about 30 nm in diameter) that contain dsRNAs (2.0 and 6.3 kbp) encapsidated by a coat of protein were detected in a mycocin-secreting strain of Cystofilobasidium infirmominiatum isolated from plants in an oak forest (Moscow region). The mycocin with a molecular mass above 15 kDa is fungicidal (maximum activity at pH 4.5) and active mainly against some species of the Cystofilobasidiales and Filobasidiales ('Cryptococcus aerius' clade). Curing by incubation at elevated temperature resulted in the concomitant loss of dsRNAs and mycocinogenic activity, and cured derivatives became sensitive to the mycocin produced by the parent strain.

[Specificity of sensitivity to mycocin from Tilletiopsis flava BKM Y-2838]

The mycocinogenous strain Tilletiopsis flava VKM Y-2823 was found to possess fungicidal activity at pH 3.5-4.5, which was retained after curing the strain by eliminating the extrachromosomal genetic elements. The mycocin produced by the strain had a molecular mass of more than 10 kDa and was readily inactivated by heating and treatment with protease K. This mycocin was found to be active against species of the anamorphic genus Tilletiopsis. The overwhelming majority of other representatives of the order Tilletiales, as well as ascomycetous and basidiomycetous yeasts, which either form or did not from ballistospores of the orders Sporidiales and Tremellales, were resistant to it.

[Importance of Bdellovibrio in regulating microbial cenoses and self-purification processes in domestic sewage]

The bacterial parasite Bdellovibrio was directly proved to be involved in the regulation of microbial cenoses and in the self-purification of domestic waste waters. The incidence of heterotrophs, Gram-negative bacteria, E. coli and Bdellovibrio was followed up in dynamics in the microecological system of waste waters for ten days. In control experiments, bdellovibrions were removed using pteridine as a vibriostatic agent. In the absence of bdellovibrions, the cell number of the studied microorganisms did not increase after reaching a stationary level. In the control, the total incidence of heterotrophs decreased 1355 times, that of Gram-negative bacteria fell down 527 times, and that of E. coli cells dropped 3419 times due to the interaction between the host bacteria and Bdellovibrio. The variations in the number of interacting cells were characteristic of a two-component parasite-host system.

[Comparative characteristics of the Bdellovibrio strains isolated from river water and sewage]

The morphology, the host ranges, the resistance to pteridine and the nucleotide composition of DNA were compared in 12 newly isolated and 10 collection strains of Bdellovibrio. The significance of properties used for the taxonomy of these organisms was evaluated. The host ranges of Bdellovibrio strains are heterogeneous with respect to the taxonomy of host bacteria. The specificity of the parasite depends to a significant degree on the host bacterium in which it grows. All the strains including Bd. starrii which was described earlier as a pteridine resistant species are sensitive to pteridine. Therefore, such properties as the host range action and the response to pteridine cannot be used for diagnostics of Bdellovibrio species. The strains were found to be very heterogeneous with regard to the nucleotide composition of the DNA. Eight out of the 12 newly isolated strains were assigned to the species Bd, bacteriovorus.