Microorganisms are pivotal in decomposing persistent organic pollutants in the environment. However, the bioavailability of pollutants is often hindered by their strong adsorption to ubiquitous fine colloids. This study provides the first evidence that Rhodococcus biphenylivorans, a known intracellular oxidative degradation bacterium, can reductively degrade organochlorine pollutants adsorbed on biochar colloids (BCCs) extracellularly, besides the oxidative degradation of BCC-adsorbed pollutants intracellularly. Over a 30 day biodegradation period, the total biodegradation rates of adsorbed 2,4,4′-trichlorobiphenyl (PCB28, 10 mg L⁻¹) on BCCs (1 g L⁻¹) prepared at pyrolysis temperatures of 300, 500, and 700 °C were 59.4%, 34.8%, and 10.4%, respectively. The biodegradation products of adsorbed PCB28 on low-temperature BCCs were mainly chlorosubstituted-2-hydroxy-6-oxo-6-phenyl-2,4-hexadienoic acid-type products, while in the high-temperature BCC system, dichlorobiphenyl was the main product. Mechanistically, BCCs with low pyrolysis temperature could fragment during the degradation, facilitating the transport of adsorbed PCB28 into bacteria for the intracellular oxidative degradation; the interactions between bacterial cells and BCCs (especially with high pyrolysis temperature) could stimulate the respiratory chain electron efflux for the extracellular dechlorination degradation. These findings not only provide new insights into the modulatory influence of BCCs on microbial degradation of pollutants, but also enrich our knowledge on the environmental fate of colloid-adsorbed pollutants.

中文翻译：

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生物炭胶体既是有机污染物的转运蛋白，也是呼吸链电子外流的兴奋剂：对吸附污染物微生物降解的新认识


微生物在分解环境中的持久性有机污染物方面起着关键作用。然而，污染物的生物利用度往往受到它们对无处不在的细胶体的强烈吸附的阻碍。本研究提供了第一个证据，证明红球菌（一种已知的细胞内氧化降解细菌）除了在细胞内氧化降解 BCC 吸附的污染物外，还可以还原降解吸附在生物炭胶体 （BCC） 上的有机氯污染物细胞外。在 30 天的生物降解期内，在 300、500 和 700 °C 的热解温度下制备的 BCC （1 g ^L-1） 上吸附的 2,4,4'-三氯联苯 （PCB28， 10 mg ^L-1） 的总生物降解率分别为 59.4%、34.8% 和 10.4%。吸附的PCB28在低温BCCs上的生物降解产物主要是氯取代-2-羟基-6-氧代-6-苯基-2,4-己二烯酸型产物，而在高温BCC体系中，二氯联苯是主要产物。从机制上讲，热解温度低的 BCC 在降解过程中会碎裂，促进吸附的 PCB28 转运到细菌中进行细胞内氧化降解;细菌细胞与 BCCs 之间的相互作用 （尤其是在高热解温度下） 可以刺激呼吸链电子外排，从而促进细胞外脱氯降解。这些发现不仅为 BCCs 对污染物微生物降解的调节影响提供了新的见解，也丰富了我们对胶体吸附污染物环境归宿的认识。