*Article* **Finding of Novel Galactose Utilizing** *Halomonas* **sp. YK44 for Polyhydroxybutyrate (PHB) Production**

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


**Abstract:** Polyhydroxybutyrate (PHB) is a biodegradable bioplastic with potential applications as an alternative to petroleum-based plastics. However, efficient PHB production remains difficult. The main cost of PHB production is attributed to carbon sources; hence, finding inexpensive sources is important. Galactose is a possible substrate for polyhydroxyalkanoate production as it is abundant in marine environments. Marine bacteria that produce PHB from galactose could be an effective resource that can be used for efficient PHB production. In this study, to identify a galactose utilizing PHB producer, we examined 16 *Halomonas* strains. We demonstrated that *Halomonas cerina* (*Halomonas* sp. YK44) has the highest growth and PHB production using a culture media containing 2% galactose, final 4% NaCl, and 0.1% yeast extract. These culture conditions yielded 8.98 g/L PHB (78.1% PHB content (*w*/*w*)). When galactose-containing red algae (*Eucheuma spinosum*) hydrolysates were used as a carbon source, 5.2 g/L PHB was produced with 1.425% galactose after treatment with activated carbon. Since high salt conditions can be used to avoid sterilization, we examined whether *Halomonas* sp. YK44 could produce PHB in non-sterilized conditions. Culture media in these conditions yielded 72.41% PHB content. Thus, *Halomonas* sp. YK44 is robust against contamination, allowing for long-term culture and economical PHB production.

**Keywords:** polyhydroxybutyrate 1; *Halomonas* sp. YK44 2; galactose 3
