Spore Photoproduct: A Key to Bacterial Eternal Life

Bacterial spores as platforms for bioanalytical and biomedical applications

Genetically engineered bacteria-based sensing systems have been employed in a variety of analyses because of their selectivity, sensitivity, and ease of use. These systems, however, have found limited applications in the field because of the inability of bacteria to survive long term, especially under extreme environmental conditions. In nature, certain bacteria, such as those from Clostridium and Bacillus genera, when exposed to threatening environmental conditions are capable of cocooning themselves into a vegetative state known as spores. To overcome the aforementioned limitation of bacterial sensing systems, the use of microorganisms capable of sporulation has recently been proposed. The ability of spores to endow bacteria-based sensing systems with long lives, along with their ability to cycle between the vegetative spore state and the germinated living cell, contributes to their attractiveness as vehicles for cell-based biosensors. An additional application where spores have shown promise is in surface display systems. In that regard, spores expressing certain enzymes, proteins, or peptides on their surface have been presented as a stable, simple, and safe new tool for the biospecific recognition of target analytes, the biocatalytic production of chemicals, and the delivery of biomolecules of pharmaceutical relevance. This review focuses on the application of spores as a packaging method for whole-cell biosensors, surface display of recombinant proteins on spores for bioanalytical and biotechnological applications, and the use of spores as vehicles for vaccines and therapeutic agents.

Photooxidation of nucleic acids on metal oxides: physico-chemical and astrobiological perspectives

Photocatalytic oxidation of nucleic acid components on aqueous metal oxides (TiO(2), α-FeOOH, and α-Fe(2)O(3)) has been studied. The oxidation of purine nucleotides results in the formation of the purine radical cations and sugar-phosphate radicals, whereas the oxidation of pyrimidine nucleotides other than thymine results in the oxidation of only the sugar-phosphate. The oxidation of the thymine (and to a far less extent for the 5-methylcytosine) derivatives results in deprotonation from the methyl group of the base. Some single stranded (ss) oligoribonucleotides and wild-type ss RNA were oxidized at purine sites. In contrast, double stranded (ds) oligoribonucleotides and DNA were not oxidized. These results account for observations suggesting that cellular ds DNA is not damaged by exposure to photoirradiated TiO(2) nanoparticles inserted into the cell, whereas ss RNA is extensively damaged. The astrobiological import of our observations is that the rapid degradation of monomer nucleotides make them poor targets as biosignatures, whereas duplex DNA is a better target as it is resilient to oxidative diagenesis. Another import of our studies is that ds DNA (as opposed to ss RNA) appears to be optimized to withstand oxidative stress both due to the advantageous polymer morphology and the subtle details of its radical chemistry. This peculiarity may account for the preference for DNA over RNA as a "molecule of life" provided that metal oxides served as the template for synthesis of polynucleotides, as suggested by Orgel and others.

Chemical investigation of light induced DNA bipyrimidine damage and repair

In all organisms, genetic information is stored in DNA and RNA. Both of these macromolecules are damaged by many exogenous and endogenous events, with UV irradiation being one of the major sources of damage. The major photolesions formed are the cyclobutane pyrimidine dimers (CPD), pyrimidine-pyrimidone-(6-4)-photoproducts, Dewar valence isomers and, for dehydrated spore DNA, 5-(α-thyminyl)-5,6-dihydrothymine (SP). In order to be able to investigate how nature's repair and tolerance mechanisms protect the integrity of genetic information, oligonucleotides containing sequence and site-specific UV lesions are essential. This tutorial review provides an overview of synthetic procedures by which these oligonucleotides can be generated, either through phosphoramidite chemistry or direct irradiation of DNA. Moreover, a brief summary on their usage in analysing repair and tolerance processes as well as their biological effects is provided.