Production of Polyhydroxyalkanoates in Unsterilized Hyper-Saline Medium by Halophiles Using Waste Silkworm Excrement as Carbon Source

Shuangfeng Cai,Shuying Yang,Yujia Shao,Yanan Li,Zhi Liu,Yan Zhao,Jianqiang Lv,Lei Cai,Yuwen Ma,Hongzhe Jia,Yaran Wu

doi:10.3390/molecules26237122

Shuangfeng Cai, Shuying Yang + Show 9 more

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https://doi.org/10.3390/molecules26237122

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Abstract

The chlorophyll ethanol-extracted silkworm excrement was hardly biologically reused or fermented by most microorganisms. However, partial extremely environmental halophiles were reported to be able to utilize a variety of inexpensive carbon sources to accumulate polyhydroxyalkanoates. In this study, by using the nile red staining and gas chromatography assays, two endogenous haloarchaea strains: Haloarcula hispanica A85 and Natrinema altunense A112 of silkworm excrement were shown to accumulate poly(3-hydroxybutyrate) up to 0.23 g/L and 0.08 g/L, respectively, when using the silkworm excrement as the sole carbon source. The PHA production of two haloarchaea showed no significant decreases in the silkworm excrement medium without being sterilized compared to that of the sterilized medium. Meanwhile, the CFU experiments revealed that there were more than 60% target PHAs producing haloarchaea cells at the time of the highest PHAs production, and the addition of 0.5% glucose into the open fermentation medium can largely increase both the ratio of target haloarchaea cells (to nearly 100%) and the production of PHAs. In conclusion, our study demonstrated the feasibility of using endogenous haloarchaea to utilize waste silkworm excrement, effectively. The introduce of halophiles could provide a potential way for open fermentation to further lower the cost of the production of PHAs.

Highlights

The massive use of traditional, nonbiodegradable plastics results in severe environmental pollution and the large consumption of nonrenewable fossil resources [1]; biodegradable plastics have become a hotspot of concern in the world today
Our previous study showed that a culture medium with less than 10% sodium chloride concentration cannot inhibit the growth of most endogenous microorganisms in silkworm excrement [24], while a medium with 15% sodium chloride concentration can
In this study, for screening the candidate strains for the open fermentation with non-sterilized silkworm excrement as the carbon source, the isolation and identification of endogenous microorganisms from silkworm excrement were carried out by using AS-165 with a 15%

Summary

Introduction

The massive use of traditional, nonbiodegradable plastics results in severe environmental pollution and the large consumption of nonrenewable fossil resources [1]; biodegradable plastics have become a hotspot of concern in the world today. In contrast to traditional petroleum-based plastics, PHAs have similar material properties but are completely degradable in a natural environment and, have many advantages, such as biocompatibility, a gas barrier, etc. The production of PHAs still has many limitations; for instance, their cost is higher than that of traditional plastics. The carbon source is the key to the synthesis of PHAs, but the cost of carbon sources in the fermentation accounts for about half of the total cost [5], which seriously hinders the large-scale production and application of PHAs in the industry

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