Characterization of polyhydroxyalkanoate (PHA)-producing bacteria
Recently, biodegradable plastics have recieved increased attention in terms of recycling-based society.
Polyhydroxyalkanoates (PHA) produced by bacteria is one of such bio-plastics and have some unique features such as biocompatibility that could be applied for the manufacture of biodegradable medical materials. We have isolated thousands of PHA-producing bacteria from various environmental niches such as seawater, soil, caves, karst and hot springs. The isolates have been analyzed in our laboratory, focusing on PHA synthase, which is the key enzyme that polymerizes PHA monomers and determines the properties of PHA plastics such as molecular weight and mechanical strength. We believe that the screening of PHA synthases could provide new insights into the properties of PHA and bacterial PHA production.

Mizuno Lab studies molecular-based microbiology of environmental and intestinal bacteria, focusing on the interaction between intestinal bacterial species, and screening of PHA (polyhydroxyalkanoate), a kind of biodegradable plastics, producing bacteria in environmental niches such as soil, seawater, hot springs, and limestone caves.

We live in a microbial world. It is said that we revealed only 5–10% of the whole microbes on the earth, which means that we have a huge resource of unknown microorganisms potentially useful for our society and that the microbes exist as the whole in which each one
mutually interacts with one another and is hard to be isolated, and thus microbial interactions should be investigated.

Mizuno Laboratory
Characterization of coaggregation between Escherichia coli and Lactobacillus species
between intestinal bacteria is thought to be important to establish and maintain a healthy microbiota in our intestine. We found coaggregates with diameters ranging from 500 to 1,000 µm in the mixed culture of Escherichia coli MG1655 and Lactobacillus species known as intestinal lactic acid bacteria. The interaction between these two intestinal bacteria required specific outer membrane structures such as fimbriae and LPS (Lipopolysaccharides) of E. coli (Mizuno et al. BBB. 2014).
APEN in a bacterial community
Recently, we found that E. coli K-12 supports the growth of some Lactobacillus species during co-culture in minimal medium via a process that requires
cell-cell contact or close proximity, but does not require fimbriae or LPS. We consider the significance of this finding in terms of ‘adjacent-possible ecological niches’ in a microbial community. The ‘adjacent-possible’ concept itself was previously proposed by the theoretical biologist Stuart Kauffman not only in the context of biology but also in a broad range of scientific fields, including economics. The species specificities and overall relevance of APENs to the LAB lifestyle, as well as the bacterial strategies targeting APENs, are intriguing questions that will need be addressed in future studies (Mizuno et al. Sci Rep 2017).
Research topics