Difference between revisions of "Team:British Columbia/Project/Consortia"

Abstract

This year, our team aims to make processing and utilization of renewable biomass feedstocks cheaper and more efficient. For this, we decided to design a microbial consortia to separated metabolic processes between two members - Caulobacter and E.coli. As microbial consortia consisting of these two bacteria has never been described before, we needed to detrmine conditions in which this bacteria are able grow together. Next we need to track dynamics of each member to ensure that one bacteria will not over-compete another. And last, as we defined the growth condition, we could start co-culturing Caulobacter displaying cellulases with E.coli producing β-carotene to confirm that our consortia can be efficient for direct transformation of lignocellulosic biomass in useful products.

Key Achievements

Introduction

Microorganisms live in complex microbial communities in the wild, in which individual species with specialized phenotypes interact and cooperate with each other to perform complex metabolic functions. Following nature's examples, there is an increasing trend in using microbial communities for biotechnological application due to their robustness and the ability to perform complex metabolic tasks through the division of labor. Construction of synthetic microbial communities allows to compartmentalize and optimize metabolic functions in different hosts. The goal of our project is to design a stable, robust microbial community for the production of valuable compounds from lignocellulosic biomass. The metabolic processes are split between biomass-degrading bacteria and the production bacteria, which transforms the degradation products into valuable products. For the first part, we engineered Caulobacter displaying functional biomass-transforming enzymes that act on cellulose. For the second part, we engineered E.coli producing β-carotene as a proof of concept. Now we need to confirm that these two bacteria can be co-cultured together to generate a stable consortia for consolidated bioprocessing.

Results

To determine the co-culture dynamics, E.coli and C.crescentus were seeded in triplicate, with each species at an initial OD600 of 0.01 with feedstock of 0.2wt% or 11.1mM glucose. Because there is no species dependence with glucose as a substrate, any negative impacts caused by co-culture should be evident in this experiment, and the compatibility of these species can be evaluated.

As predicted by the developed consortia model and in the individual species cultures, the initial growth rate of the E. coli in the co-culture was significantly higher than the growth rate of C.crescentus. At longer culture times, the growth rate of E.coli drops significantly while the growth of C. crescentus climbs steadily. The decline in E. coli growth rate, while C. crescentus growth rate is affected minimally, indicating that the glucose feedstock is not completely consumed and that oxygen becomes limiting in microwells at relatively low culture densities for E. coli.

The co-culture growth of both species indicates, in the absence of substrate limitation, E.coli and C.crescentus are compatible and there is no unexpected negative impact on community growth: a successful co-culture between E.coli and C.crescentus is possible. Another result from this experiment is the indication that the dissolved oxygen concentration must be increased in order to successfully culture and sustain a high density of E.coli using expressed cellulases on the C.crescentus surface to degrade cellulose for substrate.