Bacterial community dynamics and enhanced degradation of di-n-octyl phthalate (DOP) by corncob-sodium alginate immobilized bacteria

Abstract

A bacterial strain designated as ETG-101, capable of utilizing DOP as source of carbon and energy, was isolated from activated sludge. According to the 16s rRNA gene sequences, strain ETG-101 was identified as Burkholderia sp. Analysis of DOP degradation intermediates indicated that strain ETG-101 could completely degrade DOP via de-esterification pathway that transforms di-esters to monoesters, where DOP was transferred to M-n-O-P which in turn metabolized to phthalic acid (PA) and eventually entered into tricarboxylic acid (TCA) cycle. Further, strain ETG-101 was immobilized into complex carriers (corncob and sodium alginate). The environmental factors tests demonstrated that the immobilized cells had broader range of pH and temperature than free cells. Carrier and entrapment media significantly affected the efficiency of DOP removal in soil. Corncob-sodium alginate (SA) immobilized cells had the highest DOP removal rate of 78.1% in soil, which was 60-fold and 2.3-fold more increase in DOP removal rate compared to corncob and free cells, respectively. The bacterial quantity and community structure dynamics in soil were also investigated by the real-time quantitative PCR (q-PCR) and Illumina Miseq sequencing. The results revealed that inoculation of free cells into soil significantly reduced the bacterial quantity of soil and altered the bacterial community structure, whereas the introduction of immobilized cells to soil increased the total bacterial quantity and slightly changed the bacterial community composition. As the acclimatization, Sphingomonas and Rhodocyclus gradually disappeared when free cells were inoculated to soil. Burkholderia along with Acinetobacter, Bacteroides and Arthrobacter were the predominant genera in both free and immobilized cells systems, which were probably responsible for DOP biodegradation in soil system. Corncob-sodium alginate immobilized bacteria significantly enhanced DOP biodegradation in soil and had little impact on soil biodiversity. Therefore this immobilization method has potential in DOP-contaminated soil remediation.