Increasingly complex synthetic environmental pollutants are prompting further research into bioremediation, which is one of the most economical and safest means of environmental restoration. From the current research, using microbial consortia to degrade complex compounds is more advantageous compared to using isolated bacteria, as the former is more adaptable and stable within the growth environment and can provide a suitable catalytic environment for each enzyme required by the biodegradation pathway. With the development of synthetic biology and gene-editing tools, artificial microbial consortia systems can be designed to be more efficient, stable, and robust, and they can be used to produce high-value-added products with their strong degradation ability. Furthermore, microbial consortia systems are shown to be promising in the degradation of complex compounds. In this review, the strategies for constructing stable and robust microbial consortia are discussed. The current advances in the degradation of complex compounds by microbial consortia are also classified and detailed, including plastics, petroleum, antibiotics, azo dyes, and some pollutants present in sewage. Thus, this paper aims to support some helps to those who focus on the degradation of complex compounds by microbial consortia.

Design and construction of synthetic microbial consortia is a promising strategy to enhance the performance of bioelectrochemical systems (BESs) and to facilitate practical applications in bioenergy production. According to the design principle of “division-of-labor”, we synthesized a three-species microbial consortium for power generation, consisting of engineered Escherichia coli, Bacillus subtilis and Shewanella oneidensis. In this consortium, E. coli digested glucose to produce lactate as a carbon source and an electron donor; B. subtilis produced riboflavin as an electron shuttle; and S. oneidensis served as the exoelectrogen to generate electricity. In return, S. oneidensis oxidized lactate to acetate, which fed E. coli and B. subtilis as the carbon source. Thus, the three species formed a cross-feeding microbial consortium, which performed “better together” for power generation. As a result, glucose (11 mM, total 0.28 g) was converted to electricity for more than 15 days with high energy conversion efficiency (up to 55.7%). The microbial composition and electricity output were stable throughout the operation cycle. Furthermore, the consortium exhibited highly functional robustness to fluctuations in the initial inoculation ratio of the three strains. This system provided new insight into the rational design of more efficient, stable, and robust synthetic microbial consortia applicable in bioenergy and environmental bioremediation.

Polyethylene terephthalate (PET) biodegradation is regarded as an environmentally friendly degradation method. In this study, an artificial microbial consortium composed of Rhodococcus jostii, Pseudomonas putida and two metabolically engineered Bacillus subtilis was constructed to degrade PET. First, a two-species microbial consortium was constructed with two engineered B. subtilis that could secrete PET hydrolase (PETase) and monohydroxyethyl terephthalate hydrolase (MHETase), respectively; it could degrade 13.6% (weight loss) of the PET film within 7 days. A three-species microbial consortium was further obtained by adding R. jostii to reduce the inhibition caused by terephthalic acid (TPA), a breakdown product of PET. The weight of PET film was reduced by 31.2% within 3 days, achieving about 17.6% improvement compared with the two-species microbial consortium. Finally, P. putida was introduced to reduce the inhibition caused by ethylene glycol (EG), another breakdown product of PET, obtaining a four-species microbial consortium. With the four-species consortium, the weight loss of PET film reached 23.2% under ambient temperature. This study constructed and evaluated the artificial microbial consortia in PET degradation, which demonstrated the great potential of artificial microbial consortia in the utilization of complex substrates, providing new insights for biodegradation of complex polymers.

Astaxanthin is a natural carotenoid pigment with tremendous antioxidant activity and great commercial value. Microbial production of astaxanthin via metabolic engineering has become a promising alternative. Although great efforts have been conducted by tuning the heterologous modules and precursor pools, the astaxanthin yields in these non-carotenogenic microorganisms were still unsatisfactory for commercialization, indicating that in addition to targeted tailoring limited targets guided by rationally metabolic design, combining more globe disturbances in astaxanthin biosynthesis system and uncovering new molecular mechanisms seem to be much more crucial for further development. Since combined metabolic engineering with mutagenesis by screening is a powerful tool to achieve more global variations and even uncover more molecular targets, this study would apply a comprehensive approach integrating heterologous module engineering and mutagenesis by atmospheric and room temperature plasma (ARTP) to promote astaxanthin production in Saccharomyces cerevisiae. Here, compared to the strain with β-carotene hydroxylase (CrtZ) from Alcaligenes sp. strain PC-1, involving new CrtZ from Agrobacterium aurantiacum enhanced astaxanthin yield to 1.78-fold and increased astaxanthin ratio to 88.7% (from 66.6%). Astaxanthin yield was further increased by 0.83-fold (to 10.1 mg/g DCW) via ARTP mutagenesis, which is the highest reported yield at shake-flask level in yeast so far. Three underlying molecular targets (CSS1, YBR012W-B and DAN4) associated with astaxanthin biosynthesis were first uncovered by comparative genomics analysis. To be noted, individual deletion of CSS1 can recover 75.6% improvement on astaxanthin yield achieved by ARTP mutagenesis, indicating CSS1 was a very promising molecular target for further development. Eventually, 217.9 mg/L astaxanthin (astaxanthin ratio was 89.4% and astaxanthin yield was up to 13.8 mg/g DCW) was obtained in 5-L fermenter without any addition of inducers. Through integrating rational engineering of pathway modules and random mutagenesis of hosts efficiently, our report stepwise promoted astaxanthin yield to achieve the highest reported one in yeast so far. This work not only breaks the upper ceiling of astaxanthin production in yeast, but also fulfills the underlying molecular targets pools with regard to isoprenoid microbial overproductions.

Polyethylene terephthalate (PET) is a widely used plastic that is polymerized by terephthalic acid (TPA) and ethylene glycol (EG). In recent years, PET biodegradation and bioconversion have become important in solving environmental plastic pollution. More and more PET hydrolases have been discovered and modified, which mainly act on and degrade the ester bond of PET. The monomers, TPA and EG, can be further utilized by microorganisms, entering the tricarboxylic acid cycle (TCA cycle) or being converted into high value chemicals, and finally realizing the biodegradation and bioconversion of PET. Based on synthetic biology and metabolic engineering strategies, this review summarizes the current advances in the modified PET hydrolases, engineered microbial chassis in degrading PET, bioconversion pathways of PET monomers, and artificial microbial consortia in PET biodegradation and bioconversion. Artificial microbial consortium provides novel ideas for the biodegradation and bioconversion of PET or other complex polymers. It is helpful to realize the one-step bioconversion of PET into high value chemicals.

Polyolefins, including polyethylene (PE), polypropylene (PP) and polystyrene (PS), are widely used plastics in our daily life. The excessive use of plastics and improper handling methods cause considerable pollution in the environment, as well as waste of energy. The biodegradation of polyolefins seems to be an environmentally friendly and low-energy consumption method for plastics degradation. Many strains that could degrade polyolefins have been isolated from the environment. Some enzymes have also been identified with the function of polyolefin degradation. With the development of synthetic biology and metabolic engineering strategies, engineered strains could be used to degrade plastics. This review summarizes the current advances in polyolefin degradation, including isolated and engineered strains, enzymes and related pathways. Furthermore, a novel strategy for polyolefin degradation by artificial microbial consortia is proposed, which would be helpful for the efficient degradation of polyolefin.