Formation of chloroplast ribosomes and ribosomal RNA in Euglena incubated with protein inhibitors

Aquatic plants exposed to pharmaceuticals: effects and risks

Pharmaceuticals are biologically active, ubiquitous, low-level contaminants that are continuously introduced into the environment from both human and veterinary applications at volumes comparable to total pesticide loadings. Recent analytical advances have made possible the detection of a number of these compounds in environmental samples, raising concerns over potential nontarget effects to aquatic organisms, especially given the highly specific biologically active nature of these compounds. These concerns become paramount when the evolutionary conservation of metabolic pathways and receptors is taken into consideration, particularly in the case of aquatic plants, where a great deal of homology is displayed between the chloroplast and bacteria, as well as between other metabolic pathways across multiple phyla of biological organization. Common receptors have been identified in plants for a number of antibiotics affecting chloroplast replication (fluoroquinolones) transcription and translation (tetracyclines macrolides, lincosamides, P-aminoglycosides, and pleuromutilins), metabolic pathways such as folate biosynthesis (sulfonamides) and fatty acid biosynthesis (triclosan), as well as other classes of pharmaceuticals that affect sterol biosynthesis (statin-type blood lipid regulators). Toxicological investigations into the potency of these compounds indicates susceptibility across multiple plant species, although sensitivity to these compounds varies widely between blue-green algae, green algae, and higher plants in a rather inconsistent manner, except that Cyanobacteria are largely the most sensitive to antibiotic compounds. This differential sensitivity is likely dependent on differences in metabolic potential as well as uptake kinetics, which has been demonstrated for a number of compounds from another class of biologically active compounds, pesticides. The demonstration of conserved receptors and pathways in plants is not surprising, although it has been largely overlooked in the risk assessment process to date, which typically relies heavily on physiological and/or morphological endpoints for deriving toxicity data. However, a small number of studies have indicated that measuring the response of a pathway- or receptor-specific target in conjunction with a physiological endpoint with direct relatedness can yield sublethal responses that are two to three times more sensitive that the traditional gross morphological endpoints typically employed in risk assessment. The risk assessment for this review was based almost entirely on evaluations of gross morphological endpoints, which generally indicated that the risk pharmaceuticals pose to aquatic plants is generally low, with a few exceptions, particularly blue-green algae exposed to antibiotics, and both green and blue-green algae exposed to triclosan. It is critical to note, however, that the application of sublethal pathway or receptor-specific responses in risk assessment has largely been unconsidered, and future research is needed to elucidate whether evaluating the toxicity of pharmaceuticals using these endpoints provides a more sensitive, subtle, yet meaningful indication of toxicity than the traditional endpoints used in prospective and retrospective risk assessments for aquatic plants.

Macromolecule metabolism and photosynthetic functions in blue-green algae treated with virginiamycin, an inhibitor of protein synthesis

The M component of virginiamycin inhibited growth of Plectonema boryanum under both photoautotrophic and heterotrophic conditions. Though the S component of this antibiotic had no apparent activity per se, it enhanced the inhibitory action of its partner. Cells incubated with suitable concentrations of either M or M + S stopped growing and lysed. Loss of the colony-forming capacity occurred quickly in the presence of M + S and slowly in the presence of M alone. Virginiamycin M inhibited protein synthesis in autotrophically and heterotrophically growing Plectonema. This effect was very rapid and could be reversed by removing the antibiotic. The S component did not block the incorporation of amino acids into proteins, but prevented the reversibility of the inhibitory effect of M. Virginiamycin M or S did not affect the photosynthetic oxygen development (Hill's reaction) in Plectonema. Moreover, carbon dioxide photoassimilation and formation of chlorophyll were inhibited only after an appreciable lag. Deoxyribonucleic acid synthesis was blocked virtually without delay by virginiamycin M. Since virginiamycin inhibited protein synthesis in a similar fashion in the unicellular Anacystis nidulans, as well as in the filamentous P. boryanum, the mechanism of action of this antibiotic is probably the same in all blue-green algae.

Effect of virginiamycin on the growth cycle of Bdellovibrio

The two components of virginiamycin, virginiamycin M (VM) and virginiamycin S (VS), were used to explore the life cycle of symbiosis-dependent and -independent strains of Bdellovibrio bacteriovorus during multiplication in a two-membered system with either living or heat-inactivated Escherichia coli or in axenic cultures. Relatively high concentrations of these inhibitors separately were required to stop growth under all the conditions, but the minimum inhibitory concentration of the single components was reduced 1,000-fold by the association of VM and VS. No dissociation between mass growth and cell division was observed with VM; VS specifically halted cell division without affecting the kinetics of macromolecules formation and overall growth. This effect on cell division was only obtained when the antibiotic was added during the first half of the multiplication cycle and was reversible at any time.

Origin and metabolic properties of the RNA species formed during the replication cycle of virus 2C

When short pulses of [(3)H]uracil were administered to Bacillus subtilis infected with phage 2C, the main species of labeled RNA was a 10S component that hybridized chiefly, but not exclusively, with the heavy strand of 2C DNA. After long pulses, most of the radioactivity was found in the 23S, 16S, and 5S rRNA's, which are coded for by the cell genome. Formation of such RNA species was reduced but not suppressed upon infection, the extent of inhibition being proportional to the virus-to-cell ratio. When bacteria were incubated with virginiamycin, an inhibitor of protein synthesis, and then infected with phage 2C, formation of virus-specific RNA decreased. This antibiotic also reduced the preferential transcription of the heavy strand of 2C DNA. The methylation pattern of rRNA remained unchanged upon infection with phage 2C. Virginiamycin reduced both the methylation and stability of rRNA in uninfected cells; this effect, however, was clearly reduced during the viral cycle. It can be concluded that in 2C-infected B. subtilis, cellular and viral RNA species are simultaneously synthesized and a preferential transcription of viral message depends not only on the number of available copies of viral template, but also on their translation. Moreover, virus-dictated proteins are responsible for the inhibition of cellular RNA formation as well as for the asymmetrical transcription of phage genome. Finally, virginiamycin and phage 2C have antagonistic, nonoverlapping effects on the metabolism and function of the RNA of the host cell.