Yeast Over the Years: From Secret Fermenter to Synthetic Biology

The beginning of fermentation was first observed when yeast landed in in an open vessel of sugar rich substance several years ago before it became known that it’s simply a biological process. Yeasts are one-celled fungi. They are usually cylindrical, oval and spherical. Yeast reproduce mainly by binary fission, transverse division via spore formation and budding; a small outgrowth on the cell surface which gives rise to another new cell.
It was around 1680 when a draper from Holland Antony Van Leeuwenhoek observed this small creature under the microscope which he called "animacules". These are what we know today as bacteria, protozoa to mention a few.

Since then, various experiments were done with different strains to obtain product of special interest. For instance, the yeast Saccharomyces pastorian which is hybrid of Saccharomyces cerevisiae and Saccharomyces eubayanus could ferment or brew beer at cold temperature. Yeast is now obviously an industrial power house when it comes to brewing. There are vast majority of fermentation application apart from drinks and foods.

Saccharomyces cerevisiae

There are various modifications such as optimizing production of ethanol from corn, cassava and many cereals. On the other hand, yeast has been in the recombinant technology especially in large protein production. In the bid to improve these fermentations, scientist has been manipulating the yeast genetic materials to obtain new strain with desired and more efficient strains. These effort has been encouraged by the sequencing of Saccharomyces cerevisiae known as baker’s yeast in 1996 a move that has been in pipe line since 1989. This collective effort includes many laboratories from Asia, North America and Europe (divide and conquer strategy). This recorded the largest organism genetic material ever sequenced completely (12 million base pair in 16 chromosome) prior to the completion of human genome.

About two years ago, the synthetic yeast genome project completed and published a synthetic eukaryotic genome, Sc2.0. The aim of the project was to actually narrow out and disentangled the genetic composition of this widely studied eukaryotic species. Sc2.0’s design is a well modified Saccharomyces cerevisiae genome with an appreciable reduced size by about 8%. This has about 1.1 megabases of the genetic materials altered.

The most obvious reason apart from other reasons for the disentangled was to allow the organism grow faster. This translate to time and cost efficiency for industrial application vis-à-vis researchers. The underlining advantage of this is a simpler and well tracked genome to work with, just like a computer programmer debugging codes. If the codes were bare and elementary with only the pieces responsible for the running of the script, it becomes easier to detect the origin of the problem. The effect of streamlining the genome is synonymous to removing repeating regions such as jumping genes and nonessential genes. This makes synthetic biologist better predict the fate of modified or newly introduced pathways. Yeast is not the only organism to have its genome or natural chromosomes replaced by chemically synthesized gene. Mycoplasma mycoides a popular ruminant parasite had its genome replaced by synthetic genetic materials in 2010.

Mycoplasma mycoides

Subsequently Synthia 3.0 was derived by the splicing and removal of nonessential genes to obtain a minimal bacteria genome of 473, shorter than the 525-gene of the wild type. As a result of those studies scientists were able to discover cell replication processes, essential genes as well as delicate DNA sequence that must remain untorched.
Recently this year, researchers of Chinese Academy of Science made known in their establishing the functional single-chromosome yeast genome with all the 16 linear chromosome fused together end-to-end.

Does the number of chromosomes really matter? Gene manipulation could answer some fundamental mind provoking questions: why are some genes not essential? Why the variation in the number of chromosomes from species to species? It was a big surprise that the fusion pf the chromosomes did not substantially affect reproduction time; this is a pointer that the number of chromosomes might be less significant in organisms’ definition as one would think.

The building of chemically synthesized genome and joining of distinct chromosomes comprises the field of synthetic biology, an interdisciplinary branch of biological sciences that build artificial biology systems using the biological principles. On the other hand, this new branch of biological science helps researchers design more efficient pathways to speed up synthesis of complex molecules for instance rose oil by yeast among other medically important compounds apart from artificial building of organism’s genome.

Thank you for reading.