Conclusions
It has been recognized that methanotroph-photoautotroph cocultures offer
a highly promising biological platform for biogas conversion. Through
the interspecies metabolic coupling of methane oxidation to oxygenic
photosynthesis, the coculture can simultaneously convert both
CH4 and CO2 into microbial biomass
without external oxygen supply. However, one key obstacle in developing
methanotroph-photoautotroph based biotechnology for biogas conversion is
the lack of an effective tool for fast, accurate and frequent
characterization of the coculture growth dynamics. In this work, based
on the organism’s growth stoichiometry, the interspecies metabolic
coupling and the total mass balance, we developed an E-C protocol to
characterize the coculture. The E-C protocol provides not only accurate
estimates of the individual biomass concentration within the coculture,
but also the individual substrate consumption and product excretion
rates of each organism. To the best of our knowledge, the developed E-C
protocol is the first ever approach that could obtain individual
substrate consumption and product excretion rates for
methanotroph-photoautotroph or any other cocultures.
The accuracy of the developed E-C protocol was validated by cell
counting approach using flow cytometry. In addition, by comparing the
predicted total OD from the individual biomass concentration with the
measured total OD, we showed that the E-C protocol provided better
accuracy than the cell counting approach through statistical testing. It
is worth noting that the developed E-C protocol only requires commonly
used analytical equipment to provide quick and accurate characterization
of the methanotroph-photoautotroph cocultures.
Finally, we showed that it is very important to use static cocultures
with known concentration to validate the cell counting method, as the
cell fixation protocol could result in severely skewed cell counting
results. Currently, although cell counting with flow cytometry has
become increasingly common in determining the individual biomass
concentration in mixed culture or microbiome, very few publications have
presented validation results on their cell counting approaches.