Differences in melting temperatures of degenerated oligonucleotides targetting nitrous oxide reductase (nosZ) genes | Razlike v temperaturi taljenja začetnih oligonukleotidov za odkrivanje gena nosZ

English. One of the basic principles of molecular biology is the use oligonucleotides with comparable melting temperatures (Tm). To accommodate various evolutionary changes in target gene sequences in order to detect numerous variants of the same gene in complex microbial communities, the researchers were forced to design degenerated oligonucleotide probes and primers. In addition, recent studies suggested that relevant parameters influencing microbial activity should be included into models currently describing the final greenhouse gas emissions for public use. Further, data on microbial community structure and abundance should be included as well in near future. As one of the most potent greenhouse gases, nitrous oxide, results mainly from incomplete denitrification process, we chose nitrous oxide reductase gene (nosZ) as a model and surveyed published literature for nosZ gene oligonucleotides. We calculated in-silico Tm for each oligonucleotide degenerated variant and compared the resulting average Tm of both oligonucleotides used in pair. Degenerated oligonucleotides were found to contain variants differing in Tm for as much as 13 °C. More than 85% of oligonucleotides had difference in average Tm of paired oligonucleotide larger than 2 °C, more than 60% larger than 4 °C and more than 40% larger than 6 °C, 25% larger than 8 °C. By using such combinations at one annealing temperature or touch-down PCR or hybridization protocol, the full use of all degenerate variants could never be achieved thus bringing under the consideration the reaction chemistry. To increase the consistency of molecular results, a simple adjustment of Tm to at least comparable average Tm is recommended. In addition, critical evaluation of other methodological pitfalls should be regular practice in order to strengthen the value of molecular results as future public models parameters.

Slovenian. Eden osnovnih principov molekularne biologije je uporaba oligonukleotidov s primerljivimi temperaturami taljenja (Tm). Da bi lahko z oligonukleotidi zajeli tudi evolucijske spremembe na tarčnih sekvencah istega gena znotraj kompleksnih mikrobnih združb, so se raziskovalci zatekli k uporabi degeneriranih oligonukleotidov. Nedavne študije predlagajo vključitev za mikrobe relevantnih parametrov, ki vplivajo na njihovo aktivnost, v modele, ki se trenutno uporabljajo za opis emisij toplogrednih plinov v javnosti. V bližnji prihodnosti pa se predvideva tudi vključitev podatkov o strukturi mikrobnih združb in velikosti njihovih populacij. Ker je eden najmočnejših toplogrednih plinov, N2O, rezultat v največji meri nepopolnega poteka denitrifikacije, sva izbrala gen za reduktazo N2O (nosZ) kot model ter iz objavljene literature sestavila nabor uporabljanih oligonukleotidnih parov. Za vsako varianto degeneriranega oligonukleotida v paru sva izračunala predvideno Tm in primerjala povprečne Tm obeh oligonukleotidov v paru. Tm variant degeneriranih oligonukleotidov so se razlikovale do 13 °C. Več kot 85 % oligonukleotidov je imelo povprečno razliko Tm para > 2 °C, več kot 60 % > 4 °C in več kot 40 % oligonukleotidov je imelo Tm večjo od 6 °C. Z uporabo takih kombinacij pri eni temperaturi prileganja ali ,,PCR z zniževanjem temperature’’ ali hibridizacijskih protokolih, je praktično nemogoče zagotoviti polno uporabo vseh degeneriranih variant. Našteto posledično različno vpliva na potek kemijskih reakcij prepoznave tarčnih mest. Da bi izboljšali konsistentnost molekularnih rezultatov, priporočava uskladitev povprečnih Tm para oligonukleotidov. Podobno pa je potrebno kritično oceniti druge metodološke šibke točke, da bi zagotovili uporabno vrednost rezultatov molekularnih tehnik kot bodočih parametrov v modelih.