Vassili V Velkov
Articles written in Journal of Biosciences
Volume 24 Issue 3 September 1999 pp 279-286 Articles
Changes in the activity of key enzymes of the methanol utilization pathway of the recombinant strains of methylotrophic yeast
Volume 24 Issue 4 December 1999 pp 529-559 Review
This review is focused on the physiological and evolutionary strategies of the processes occurring during the entry of microbial cells into stationary phase and the subsequent period of stasis. The molecular mechanisms adapting microorganisms from exponential growth to a static state involve activation and complex regulation of the stationary factor Sigma-S, which directs RNA polymerase to the specific promoters. As a result the static cells acquire general resistance (simultaneous tolerances) to different environmental stresses. In parallel with the physiological adaptation to stasis, diverse genetical processes are aimed towards resuming the growth of the static cells. Different types of mutagenesis occur: (i) in cells entering stasis and (ii) in static cells (adaptive mutagenesis). Cessation of growth induces the transient hypermutator state resulting in the accumulation of random mutations in the subpopulation of the static cells. If by chance, one or a few of such mutations lead to resumption of division, the growing cell will return to a normal mechanism of spontaneous mutagenesis.
Another mechanism for generating genetical variability in stressed cells involves transposons and conjugative plasmids. Stresses can stimulate the excision of some transposons, which, in turn, can generate chromosomal mutations and activate intracellular mechanisms of mutagenesis. Under stress some conjugative plasmids activate genes encoding antirestriction proteins that repress restriction-modification systems of the recipient cells. Moreover, under stress special cellular mechanisms decrease (alleviate) the activity of restriction-modification systems which, in turn, enhance the probability of gene transfer into the stressed cells.
Under stress, the efficiency of inter-species genetical barriers also decreases. This, stimulates inter-species gene transfer and may lead to a burst of incipient speciation in the population of non-growing cells. After resumption of growth the genetical barriers leading to isolation will be restored.
In general, the cessation of growth “switches on”, and resumption of growth “switches off”, a set of special processes that are responsible for generating bursts of genetical variability in populations of microorganisms.
Volume 25 Issue 2 June 2000 pp 125-131
Volume 26 Issue 5 December 2001 pp 667-683 Review
This article is focused on the problems of reduction of the risk associated with the deliberate release of genetically modified microorganisms (GMMs) into the environment. Special attention is given to overview the most probable physiological and genetic processes which could be induced in the released GMMs by adverse environmental conditions, namely: (i) activation of quorum sensing and the functions associated with it, (ii) entering into a state of general resistance, (iii) activation of adaptive mutagenesis, adaptive amplifications and transpositions and (iv) stimulation of inter-species gene transfer. To reduce the risks associated with GMMs, the inactivation of their key genes responsible for stress-stimulated increase of viability and evolvability is proposed.
Volume 30 Issue 4 September 2005 pp 515-548 Review
Transgenic insecticidal plants based on