A seawater-based open and continuous process for polyhydroxyalkanoates production by recombinant Halomonas campaniensis LS21 grown in mixed substrates

Background: High-cost production of bioplastics polyhydroxyalkanoates (PHA) is a major concern for their large scale application. In order to produce PHA economically, new technology must be developed to reduce costs on energy consumption, fresh water and substrate usages. It is also important to conduct the PHA production process in a continuous way rather than in a batch process. Results: A halophile Halomonas campaniensis strain LS21 was isolated to allow the development of a sea water based open and continuous process for PHA production utilizing mixed substrates consisting of mostly cellulose, starch, lipids and proteins. To study the feasibilities of open and long-term cultivation as well as genetic manipulation of this strain, polyhydroxybutyrate (PHB), the first member of the diverse PHA family, was taken as an example for the application of H. campaniensis LS21 in a robust and long lasting fermentation process. Wild type and recombinant H. campaniensis LS21 containing a PHB synthesis genes phbCAB were allowed respectively to grow in artificial seawater containing mixed substrates similar to kitchen wastes, including soluble and insoluble cellulose, proteins, fats, fatty acids and starch for 65 days without interruption. In the presence of 27 g/L NaCl under a pH around 10 at 37 C, the recombinant produced approximately 70% PHB and the wild type 26% during the 65 days fermentation process without infection. H. campaniensis LS21 secreted extracellular amylase, lipase, protease and cellulase simultaneously during the whole process to allow consumption of the mixed substrates. The recombinant was also found to stably maintain the phbCAB plasmid over the entire 65 days process. Conclusions: The seawater based open and continuous process based on halophilic Halomonas campaniensis LS21 allowed the applications of kitchen wastes like mixed substrates as nutrients for production of bioplastic PHB. This study demonstrates the advantages of this technology in terms of energy saving (non-sterilization), seawater based (not fresh water needed), long-lasting and continuous open processing (against batch process), and low cost substrates (non-food mixed substrates). Combined with its ease of genetic manipulation, Halomonas campaniensis LS21 could be developed into a platform for low cost production of chemicals, materials and biofuels.