Biotransformations of HBCDs by Rhodococcus Strain Stu-38 and Identification of Transformation Products

1, 2, 5, 6, 9, 10-Hexabromocyclododecanes (HBCDs) are new brominated flame retardants causing serious environmental pollution. Dozens of degradative bacteria have been found with capacity to transform HBCDs. In the present study, an aerobic functional bacterium Rhodococcus strain stu-38 was isolated from enriched culture of mangrove sediment using HBCDs as carbon source. This strain could stereoselectively transform HBCDs, the removal rate was α-＞γ-＞β-HBCD in the mineral salt medium, but was β-＞α- and γ-HBCD in the growth medium, and it selectively transformed γ- HBCD in the seawater. Transformation rate of strain stu-38 was lower than other functional strains, however, seven potential debrominated products of HBCDs were identified by using GC-MS. These debrominated products, included dibromocyclododecadiene, bromocyclododecadienol and bromocyclododecatriene were formed through reductive debromination, hydrolytic debromination and dehydrobromination. Overall, Rhodococcus sp. stu-38 diastereoisomer-specifically transformed HBCDs to various debrominated products in the different cultural media, which highlighted the complicated stereoselective biotransformation of HBCDs.

A Pesticide Biopurification System: A Source of Biosurfactant-Producing Bacteria with Environmental Biotechnology Applications

Biosurfactants, a wide group of compounds produced by different microorganisms, generally have less toxicity and are more biodegradable than synthetic surfactants. Biosurfactant-producing bacteria can be found in contaminated environments, such as soils receiving pesticide applications constantly, or in pesticides treatment systems where microorganisms are adapted to biodegrading pesticides. Five pesticide-tolerant bacteria previously isolated from a pesticide biopurification system were evaluated as biosurfactant-producers. Pseudomonas rhodesiae C4, Rhodococcus jialingiae C8 and Pseudomonas marginalis C9 strains were positive in qualitative tests. Biosurfactant production by these strains using Bushnell-Haas medium with olive oil at 2% (w/v) was evaluated as emulsification index, oil displacement, droplet collapse test and surface tension. After 144 h, these strains showed a similar emulsification index of >55%. The two Pseudomonas (C4 and C9) strains showed lower superficial tension compared with Rhodococcus strain (C8)—34.47, 37.44 and 47.55 mN/m for strains C4, C9 and C8, respectively. The chemical characterization of the biosurfactants revealed the presence of glycolipids in P. rhodesiae (C4) and glycopeptides in P. marginalis (C9). The degradation of chlorpyrifos increased from 39.2% to 51.6% when biosurfactants produced by P.rhodesiae (C4) were added (10%) with respect to the control. Therefore, biopurification systems are a relevant source of biosurfactant-producing bacteria with environmental biotechnology applications.