1. science
2. biology

Evolution of Microbial Systems
Dr. Shun Adachi
Assistant Professor
Institute of Biomedical Sciences
Tokushima University
Time: 2015. 04. 20 Mon. 15:00
Venue: Auditorium, 1st Floor
Interdisciplinary Research Building
跨領域科技研究大樓1 樓演講廳
Host: Dr. Sen-Lin Tang 湯森林副研究員
Abstract
In molecular biology, microbial systems are useful for their handiness in experimental
techniques and have had major roles on systems biology. However, relatively little is known
about their actual ecology and evolution. I am interested in study for evolution of microbial
systems, especially for species problem that is distinguishable concept from ordinary ideas
in physics or chemistry, by utilizing molecular techniques such as genetics and imaging
available.
In this seminar, I first present understanding systemic bases of a model organism
Escherichia coli by faithful positioning and segregation of the sex factor F plasmid and an
adaptive transportation mechanism for chromosome segregation without microfilaments.
Previously we studied chromosome and plasmid segregation machineries of E. coli by
molecular biological methods and bioimaging, resulting in explanation of F plasmid
positioning activity by Turing’s reaction-diffusion system (J Mol Biol 356: 850.). The
question was how the equidistant positioning of plasmid DNA molecules is achieved for
proper segregation of the plasmid. We speculated the mechanism as a reaction-diffusion
system, and by bioimaging and modeling, we proposed the model. The scheme was proved
by a different group in homologous Min system later, at least in vitro (Science 320: 789.). We
have also elucidated intracellular protein-protein interaction network of E. coli chromosome
segregation acting as molecular ‘tether’ for adaptive transportations of the chromosomes
(Microbiology 160: 1648.; Front Microbiol 6: 75.). The chromosome segregation mechanism
in bacteria without microfilaments is a long-held mystery. However, Fisher et al. (2013) Cell
153: 882. proposed a new model that described a hypothetical molecular ‘tether’, which
undergoes stressing and releasing cycles against chromosomal DNA, could mediate such a
process. We searched for actual molecules that could be the ‘tether’ and found out a Sectranslocon interacting molecular network could be such a tether.
After the notes for molecular biology, I expand the study to the scaling difference of adaptive
species and neutral populations in Dictyostelia community in wild (Evol Biol doi:
10.1007/s11692-015-9312-0.). I distinguish the distributions of populations and species, and
the phenomenon might be due to different time scale of the two criteria, characterized by
ecological neutrality and adaptation to the environments. This might be a starting point to
understand what species is, from ecological aspects.
From now on I would like to focus on evolutionary biology based on molecular/genomic
biology, bioimaging and modeling. My future themes for studying evolution are (i)
postzygotic reproductive isolation by chromosome dynamics of Malaysian Saccharomyces
cerevisiae, and (ii) social biology and newly proposed ‘size matter’ hypothesis in
Dictyostelium discoideum. The questions for (i) are what are the factors related to
postzygotic reproductive isolation in budding yeast, and whether the factors are universal
among eukaryotes or not. I speculate and show some evidence that chromosome dynamics
plays a prominent role in the isolation, together with future plans to expand the study. The
study is an approach toward species problem from molecular biology. The question for (ii) is
whether there is a particular size limit of populations related to social requirements. I
speculate that DNA repair, ageing and reproductive isolation play prominent roles, and by
evolutionary experiments with D. discoideum I try to propose how social games affects
hierarchical structures of the living organism as observed. The study is an approach toward
biological hierarchies, not restricted to species, from social biology.