Pigments accumulation via light and oxygen in Rhodobacter capsulatus strain XJ-1 isolated from saline soil

Enhanced pollutants removal and high-value cell inclusions accumulation with Fe2+ in heavy oil refinery treatment system using Rhodopseudomonas and Pseudomonas

Metal ions has been widely used as a method of improving pollutant removal efficiency in wastewater biological treatment system. In order to enhance pollutants removal and high-value cell inclusions accumulation in heavy oil refinery wastewater treatment systems using PSB, different reactors were built feeding with different Fe²⁺ concentrations respectively, and run with enriching Rhodopseudomonas and Pseudomonas in the reactors. Solute chemical oxygen demand (SCOD), ammonia (NH₄⁺-N), nitrate nitrogen (NO₃^--N), nitrous nitrogen (NO₂^--N), Fe²⁺, and related cell inclusions were all detected, moreover, microbial community structure and the quantity of Rhodopseudomonas and Pseudomonas were also detected. The results showed that at the optimal dosage of Fe²⁺ with 20 mg/L, the corresponding removal ratios of solute chemical oxygen demand and ammonia were 73.51% and 92.26%, respectively. The yields of carotenoid, bacteriochlorophyll, and coenzyme Q₁₀ were 11.18, 6.75, and 9.84 mg/g-DCW respectively. Furthermore, with 20 mg/L Fe²⁺ dosage, the relative abundance and gene number of Rhodopseudomonas were the highest in the system, which were 91.57% and 1.843 × 10⁶ gene copies/μL, while Fe²⁺ had no obvious effect on the growth of Pseudomonas. The results showed that adding Fe²⁺ has improved the removal of pollutants and accumulation of high-value cells inclusions, also provided theoretical guidance for the treatment of heavy oil refinery wastewater using PSB.

Functional replacement of isoprenoid pathways in Rhodobacter sphaeroides

Advances in synthetic biology and metabolic engineering have proven the potential of introducing metabolic by-passes within cell factories. These pathways can provide a more efficient alternative to endogenous counterparts due to their insensitivity to host's regulatory mechanisms. In this work, we replaced the endogenous essential 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway for isoprenoid biosynthesis in the industrially relevant bacterium Rhodobacter sphaeroides by an orthogonal metabolic route. The native 2-C-methyl-D-erythritol 4-phosphate (MEP) pathway was successfully replaced by a heterologous mevalonate (MVA) pathway from a related bacterium. The functional replacement was confirmed by analysis of the reporter molecule amorpha-4,11-diene after cultivation with [4-13 C]glucose. The engineered R. sphaeroides strain relying exclusively on the MVA pathway was completely functional in conditions for sesquiterpene production and, upon increased expression of the MVA enzymes, it reached even higher sesquiterpene yields than the control strain coexpressing both MEP and MVA modules. This work represents an example where substitution of an essential biochemical pathway by an alternative, heterologous pathway leads to enhanced biosynthetic performance.