苯系物降解菌的筛选及改进补料策略的PHA生产

Screening of Aromatic Hydrocarbons-degrading Bacteria and Production of PHA by an Improved Feeding Strategy

苯、甲苯、乙苯、二甲苯(BTEX)是废气中常见且难被消除的有机污染物。微生物将其降解并转化成聚羟基脂肪酸酯(PHA),可在消除污染的同时实现变废为宝的双重功效。该研究从活性污泥中筛选到多种可将BTEX转化成聚羟基脂肪酸酯(PHA)的菌株,3株较强PHA合成菌被分别鉴定为Pseudomonas fulva TY16、Pseudomonas putida MY21和Pseudomonas fluorescence SX11。其含不同的BTEX降解基因,对BTEX各种物质的降解效果也有所不同。当甲苯初始浓度超过1.5 g/L时,TY16菌株的生长会受其毒性作用而受到抑制。通过注射器动力泵精确提供碳源,并通过气态形式给料,其毒副作用的影响得以解决,当甲苯按设计补料速率进行分批补料发酵时,培养40 h后,菌体干重可达3.8 g/L,胞内积累PHA含量达总干重的58%,其PHA转化率提升至0.315 g/g。相比于利用空气流量计作为碳源提供方式的转化率0.113 g/g,增加了近3倍。

Benzene, toluene, ethylbenzene, xylene（BTEX） are types of contaminants that are common and also very difficult to remove among volatile organic compounds. The method of utilizing microorganism to degrade BTEX and then converting into polyhydroxyalkanoate（PHA）, has a double effect not only in pollutant disposing but also for recycling into environmental-friendly products. In this study, microorganisms capable of converting BTEX compounds to polyhydroxyalkanoate（PHA） were isolated from activated sludge by enrichment process. Among the isolates, three strains, identified as Pseudomonas fulva TY16, Pseudomonas putida MY21, and Pseudomonas fluorescence SX11, were selected for further study. These strains possessed different aromatic hydrocarbon-degrading genes and showed different degradation patterns towards BTEX compounds. The growth of strain TY16 was significantly decreased when the initial concentration of toluene in the medium exceeded 1.5 g/L. This problem could be successfully resolved by a novel continuous feeding system of gaseous aromatic substrates using a syringe pump. In fed-batch experiments, where toluene was constantly supplied to the fermentor at a defined flow rate, the growth of TY16 reached 3.8 g/L of dry cell weight（DCW） after 40 h of cultivation and the cellular content of accumulated PHA was 58% of DCW. In this case, the conversion yield was 0.315 g/g, increasing about three times compared with 0.113 g/g obtained from a fermentation experiment with conventional airflow meter feeding system.