High-level production of poly (β-l-malic acid) with a new isolated Aureobasidium pullulans strain

Abstract

Poly (β-L: -malic acid) (PMLA) is a water-soluble polyester with many attractive properties in chemical industry and medicine development. However, the low titer of PMLA in the available producer strains limits further industrialization efforts and restricts its many potential applications. In order to solve this problem, a new strain with the distinguished high productivity of PMLA was isolated from fresh plants samples. It was characterized as the candidate of Aureobasidium pullulans based on the morphology and phylogenetic analyses of the internal transcribed spacer sequences. After the optimization of culture conditions, the highest PMLA concentration (62.27 g l(-1)) could be achieved in the shake flask scale. In addition, the contribution of the carbon flux to exopolysaccharide (EPS) and PMLA could be regulated by the addition of CaCO₃ in the medium. This high-level fermentation process was further scaled up in the 10 l benchtop fermentor with a high PMLA concentration (57.2 g l(-1)) and productivity (0.35 g l(-1) h(-1)), which are the highest level in all the literature. Finally, the suitable acid hydrolysis conditions of PMLA were also investigated with regard to the production of L: -malic acid, and the kinetics of PMLA acid hydrolysis was modeled to simulate the whole degradation process. The present work paved the road to produce this multifunctional biomaterial (PMLA) at industrial scale and promised one alternative method to produce L: -malic acid in the future.

Intensification of β-poly(l-malic acid) production by Aureobasidium pullulans ipe-1 in the late exponential growth phase

“…In the early exponential growth phase, PMLA production was associated with cell growth, whereas the dissociation between the PMLA production and cell growth appeared after 48 h of cultivation. The dissociation between PMLA production and cell growth in the late exponential growth phase was reported by Nakajima-Kambe et al [18], Liu and Steinbüchel [15], and Zhang et al [24]. However, Nakajima-Kambe et al [18] found that PMLA was mainly produced in the late exponential and stationary phases when PMLA was produced by Aureobasidium sp.…”

“…These diVerences could be caused by the diVerent strains and experimental conditions used by diVerent investigators. By summarizing previous literature, Zhang et al [24] also showed that the production levels of PMLA varied a lot among the strains previously used, i.e., P. polycephalum, Aureobasidium sp. A-91, A. pullulans CBS 591.75, and A. pullulans ZD-3d.…”

“…However, Nakajima-Kambe et al [18] found that PMLA was mainly produced in the late exponential and stationary phases when PMLA was produced by Aureobasidium sp. A-91 in Xasks; Liu and Steinbüchel [15] reported PMLA production by A. pullulans CBS 591.75 in a 1-l bioreactor was almost unrelated to cell growth, and production of large amounts of PMLA started only in the late exponential growth phase; whereas Zhang et al [24] found that PMLA concentration in a 10-l bioreactor rapidly increased during the exponential and stationary phases in batch fermentation with A. pullulans ZD-3d. These diVerences could be caused by the diVerent strains and experimental conditions used by diVerent investigators.…”

“…Leathers et al [17] did signiWcant work on PMLA production by strains of Aureobasidium pullulans representing genetically diverse phylogenetic clades, some of which included strains produced relatively high levels of PMLA. Zhang et al [24] also reported a new strain, characterized as the candidate of A. pullulans on the basis of the morphology and phylogenetic analyses of internal transcribed spacer sequences; this strain was isolated from fresh plants samples and gave a high PMLA productivity of 0.35 g l ¡1 h ¡1 in a 10-l bioreactor. However, there are discrepancies regarding the relationship between cell growth and PMLA production in the literature.…”

“…On the other hand, some confusing phenomena relating to cell growth and PMLA production have been reported to occur in bioreactors. Zhang et al [24] found the cell growth of A. pullulans and PMLA concentration in a 10-l bioreactor rapidly increased during the exponential and stationary phases, whereas Liu and Steinbüchel [15] reported that PMLA production was almost unrelated to cell growth and PMLA was largely yielded in the late exponential growth phase when A. pullulans CBS 591.75 was cultivated in a 1-l fermenter. Unfortunately, no detailed explanation was presented in their work.…”