报告题目：The Evolution of Microbial Ecology
报 告 人：Linda Blackall, Professor
Swinburne University of Technology, Australia
Abstract：By 2012, researchers had proposed numerous, sometimes contentious hypotheses on the origin of cellular life on earth, that were explored by experiments. Key unifying features indicate that cellular life on earth evolved about 1 billion years after the earth was formed. Thus, the last universal common ancestor (LUCA) probably arose between 4.2 and 3.4 billion years ago from inorganic matter, a notion sustained by the Urey-Miller experiment. The first cellular organisms are thought to lack a nucleus and to have evolved from protobionts, which are organic molecules surrounded by a lipid bilayer membrane. Prokaryotes (bacteria and archaea) likely evolved from protobionts, and were the sole cellular organisms on earth for the first 3 billion years of cellular life.
Until the 1980s, microbiologists studied bacteria by isolating them in pure culture on agar media (incubated under specific conditions of temperature, pressure and atmosphere) and defining their taxonomy by determining aspects of their phenotype (e.g. sole carbon sources for growth, etc.) and their genotype (e.g. mol% G+C of the genome). Early analyses of prokaryotic 16S RNAs (oligonucleotide cataloguing on 2D polyacrylamide gels), demonstrated (initially to Carl Woese) that there were two evolutionarilydifferent groups, called bacteria and archaea. Thus, the term “prokaryote” became redundant (sensu Norman Pace).
How did microbial ecology evolve? Development of methods was crucial. PCR using “universal” 16S rRNA gene primers with DNA isolated from complex microbial communities lead to the understanding that microbial diversity was tremendously greater than imagined and that taxonomy based on phenotype was flawed. Metagenomics was born and several complex microbial communities were subjected to this procedure. This led to some comprehension of resident microorganisms and genes in the community. Methods for DNA sequencing generated enormous volumes of data that outstripped the capacity for their analyses.
So here we are with loads of microbial community DNA sequence data that can be correlated with data from similar or dissimilar environments. Conclusions from this correlative exercise are drawn. But what of the function of the microbes in any environment? An operon for a particular phenotype might be revealed in a metagenomic analysis. Does any community member have this phenotype? This cannot be unequivocally addressed by metagenomic analyses.
Microbial ecology is a field in evolution. It will continue to inform us about critical aspects of life on earth.