Intracellular Metabolic Changes of Rhodococcus sp. LH During the Biodegradation of Diesel Oil

Enhanced degradation of phthalate esters (PAEs) by biochar-sodium alginate immobilised Rhodococcus sp. KLW-1

In this study, a new strain of bacteria, named Rhodococcus sp. KLW-1, was isolated from farmland soil contaminated by plastic mulch for more than 30 years. To improve the application performance of free bacteria and find more ways to use waste biochar, KLW-1 was immobilised on waste biochar by sodium alginate embedding method to prepare immobilised pellet. Response Surface Method (RSM) predicted that under optimal conditions (3% sodium alginate, 2% biochar and 4% CaCl2), di (2-ethylhexyl) phthalate (DEHP) degradation efficiency of 90.48% can be achieved. Under the adverse environmental conditions of pH 5 and 9, immobilisation increased the degradation efficiency of 100 mg/L DEHP by 16.42% and 11.48% respectively, and under the high-stress condition of 500 mg/L DEHP concentration, immobilisation increased the degradation efficiency from 71.52% to 91.56%, making the immobilised pellets have strong stability and impact load resistance to environmental stress. In addition, immobilisation also enhanced the degradation efficiency of several phthalate esters (PAEs) widely existing in the environment. After four cycles of utilisation, the immobilised particles maintained stable degradation efficiency for different PAEs. Therefore, immobilised pellets have great application potential for the remediation of the actual environment.

Degradation of petroleum hydrocarbon contaminants by Rhodococcus erythropolis KB1 synergistic with alfalfa (Medicago sativa L.)

Petroleum hydrocarbons are a stubborn pollutant that is difficult to degrade globally, and plant-microbial degradation is the main way to solve this type of pollutant. In this study, the physiological and ecological responses of alfalfa to petroleum hydrocarbons in different concentrations of petroleum hydrocarbon-contaminated soil with KB1 (Rhodococcus erythropolis) were analyzed and determined by laboratory potting techniques. The growth of alfalfa (CK) and alfalfa with KB1 (JZ) in different concentrations of petroleum hydrocarbons contaminated soil was compared and analyzed. The results of the CK group showed that petroleum hydrocarbons could significantly affect the activity of alfalfa antioxidant enzyme system, inhibit the development of alfalfa roots and the normal growth of plants, especially in the high-concentration group. KB1 strain had the ability to produce IAA, form biofilm, fix nitrogen, produce betaine and ACC deaminase, and the addition of KB1 could improve the growth traits of alfalfa in the soil contaminated with different concentrations of petroleum hydrocarbons, the content of soluble sugars in roots, and the stress resistance and antioxidant enzyme activities of alfalfa. In addition, the degradation kinetics of the strain showed that the degradation rate of petroleum could reach 75.2% after soaking with KB1. Furthermore, KB1 can efficiently degrade petroleum hydrocarbons in advance and significantly alleviate the damage of high concentration of petroleum hydrocarbons to plant roots. The results showed that KB1 strains and alfalfa plants could effectively enhance the degradation of petroleum hydrocarbons, which provided new ideas for improving bioremediation strategies.

Rhodococcus: A promising genus of actinomycetes for the bioremediation of organic and inorganic contaminants

Rhodococcus is a genus of actinomycetes that has been explored by the scientific community for different purposes, especially for bioremediation uses. However, the mechanisms governing Rhodococcus-mediated bioremediation processes are far from being fully elucidated. In this sense, this work aimed to compile the recent advances in the use of Rhodococcus for the bioremediation of organic and inorganic contaminants present in different environmental compartments. We reviewed the bioremediation capacity and mechanisms of Rhodococcus spp. in the treatment of polycyclic aromatic hydrocarbons, phenolic substances, emerging contaminants, heavy metals, and dyes given their human health risks and environmental concern. Different bioremediation techniques were discussed, including experimental conditions, treatment efficiencies, mechanisms, and degradation pathways. The use of Rhodococcus strains in the bioremediation of several compounds is a promising approach due to their features, primarily the presence of appropriate enzyme systems, which result in high decontamination efficiencies; but that vary according to experimental conditions. Besides, the genus Rhodococcus contains a small number of opportunistic species and pathogens, representing an advantage from the point of view of safety. Advances in analytical detection techniques and Molecular Biology have been collaborating to improve the understanding of the mechanisms and pathways involved in bioremediation processes. In the context of using Rhodococcus spp. as bioremediation agents, there is a need for more studies that 1) evaluate the role of these actinomycetes on a pilot and field scale; 2) use genetic engineering tools and consortia with other microorganisms to improve the bioremediation efficiency; and 3) isolate new Rhodococcus strains from environments with extreme and/or contaminated conditions aiming to explore their adaptive capabilities for bioremediation purposes.

Efficient ammonia production from food by-products by engineered Escherichia coli

Ammonia is used as a fertilizer for agriculture, chemical raw material, and carrier for transporting hydrogen, and with economic development, the demand for ammonia has increased. The Haber-Bosch process, which is the main method for producing ammonia, can produce ammonia with high efficiency. However, since it consumes a large amount of fossil energy, it is necessary to develop an alternative method for producing ammonia with less environmental impact. Ammonia production from food by-products is an appealing production process owing to unused resource usage, including waste, and mild reaction conditions. However, when food by-products and biomass are used as feedstocks, impurities often reduce productivity. Using metabolic profiling, glucose was identified as a potential inhibitor of ammonia production from impure food by-products. We constructed the recombinant Escherichia coli, in which glucose uptake was reduced by ptsG gene disruption and amino acid catabolism was promoted by glnA gene disruption. Ammonia production efficiency from okara, a food by-product, was improved in this strain; 35.4 mM ammonia was produced (47% yield). This study might provide a strategy for efficient ammonia production from food by-products.