Development of a cost-effective production process for Halomonas levan

Abstract

Levan polysaccharide is an industrially important natural polymer with unique properties and diverse high-value applications. However, current bottlenecks associated with its large-scale production need to be overcome by innovative approaches leading to economically viable processes. Besides many mesophilic levan producers, halophilic Halomonas smyrnensis cultures hold distinctive industrial potential and, for the first time with this study, the advantage of halophilicity is used and conditions for non-sterile levan production were optimized. Levan productivity of Halomonas cultures in medium containing industrial sucrose from sugar beet and food industry by-product syrup, a total of ten sea, lake and rock salt samples from four natural salterns, as well as three different industrial-grade boron compounds were compared and the most suitable low-cost substitutes for sucrose, salt and boron were specified. Then, the effects of pH control, non-sterile conditions and different bioreactor modes (batch and fed-batch) were investigated. The development of a cost-effective production process was achieved with the highest yield (18.06 g/L) reported so far on this microbial system, as well as the highest theoretical bioconversion efficiency ever reported for levan-producing suspension cultures. Structural integrity and biocompatibility of the final product were also verified in vitro.

Production of levan by Bacillus licheniformis NS032 in sugar beet molasses-based medium

“…1. Control of pH value has proved to be one of the most important factors in optimizing the fermentation medium, not only for B. licheniformis NS032, but also for other levan producers [14,27,28,29].…”

Engineering self‐flocculating Halomonas campaniensis for wastewaterless open and continuous fermentation

“…Chen et al, 2017;Erkorkmaz, Kırtel, Ateş Duru, & Toksoy Öner, 2018;Fu et al, 2014;Jiang et al, 2017;Yue et al, 2014). with some successes (X.…”

“…with some successes (X. Chen et al, 2017;Erkorkmaz, Kırtel, Ateş Duru, & Toksoy Öner, 2018;Fu et al, 2014;Jiang et al, 2017;Yue et al, 2014). The continuous processes demand continuous biomass collection and product purification, leading to increased process complexity (Brethauer & Wyman, 2010;Lynd, Grethlein, & Wolkin, 1989).…”

Effect of temperature on the hydrolysis of levan treated with compressed hot water fluids

“…Microbial levan can serve a variety of purposes, including forming an important component of biofilms, shielding microorganisms from desiccation, increasing the virulence of plant pathogens, forming an oxygen diffusional barrier, and serving as an extracellular nutrient reservoir. Unlike other natural polymers, levan self‐assembles into spherical colloids with low intrinsic viscosity and high biocompatibility (Adnan Erkorkmaz, Kirtel, Duru, & Toksoy Öner, 2018). “Green” processes involving the conversion of microbial levan into industrial products and (particularly) food additives offer further possibilities for sustainable commercial development (Ortiz & García, 2010).…”

“…Blake, Clarke, Jansson, and McNeil (1982) investigated levan production from a strain of the gram‐negative bacterium Erwinia herbicola ( E. herbicola ) (isolated from a crushing mill at a sugar factory), and this product is now commercially available. Halomonas smyrnensis ( H. smyrnensis ) AAD6T was reported by Poli et al (2009) as the first halophilic, levan‐producing microorganism, facilitating levan production under non‐sterile conditions by use of high‐salinity medium (Adnan Erkorkmaz et al, 2018).…”