*Article* **Finding a Benign Plasticizer to Enhance the Microbial Degradation of Polyhydroxybutyrate (PHB) Evaluated by PHB Degrader** *Microbulbifer* **sp. SOL66**

**Jang Yeon Cho 1, Su Hyun Kim 1, Hee Ju Jung 1, Do Hyun Cho 1, Byung Chan Kim 1, Shashi Kant Bhatia <sup>1</sup> , Jungoh Ahn <sup>2</sup> , Jong-Min Jeon <sup>3</sup> , Jeong-Jun Yoon <sup>3</sup> , Jongbok Lee <sup>4</sup> and Yung-Hun Yang 1,\***


**Abstract:** As a biodegradable plastic, polyhydroxybutyrate (PHB) has relatively poor mechanical properties, preventing its wider use. Various plasticizers have been studied to improve the mechanical properties of PHB; however, due to the slow degradation speed in the soil environment and lack of evaluation methods, studies on the degradation of PHB with plasticizers are rarely reported. In this study, by applying *Microbulbifer* sp. SOL66, which is able to degrade PHB very quickly, a benign plasticizer was evaluated with good properties and good degradability, not inhibiting microbial activities. Eight different plasticizers were applied with PHB and *Microbulbifer* sp. SOL66, PHB film containing 10% and 20% tributyl citrate showed significant biodegradability of PHB. It was confirmed that tributyl citrate could increase the speed of PHB degradation by *Microbulbifer* sp. SOL66 by 88% at 1 day, although the degree of degradation was similar after 3 days with and without tributyl citrate. By the analysis of microbial degradation, physical, chemical, and mechanical properties, tributyl citrate was shown not only to improve physical, chemical, and mechanical properties but also the speed of microbial degradation.

**Keywords:** polyhydroxybutyrate; plasticizer; biodegradation; *Microbulbifer* sp. SOL66
