Production of poly (3-hydroxybutyrate) and extracellular polymeric substances from glycerol by the acidophile Acidiphilium cryptum

Abstract

Acidiphilium cryptum is an acidophilic, heterotrophic, and metallotolerant bacteria able to use dissolved oxygen or Fe(III) as an electron sink. The ability of this extremophile to accumulate poly(3-hydroxybutyrate) (PHB) and secrete extracellular polymeric substances (EPS) has also been reported. Hence, the aim of this work is to characterize the production of PHB and EPS by the wild strain DSM2389 using glycerol in shaken flasks and bioreactor. Results showed that maximum PHB accumulation (37-42% w/w) was obtained using glycerol concentrations of 9 and 15 g L −1 , where maximum dry cell weight titers reached 3.6 and 3.9 g L −1 , respectively. The culture in the bioreactor showed that PHB accumulation takes place under oxygen limitation, while the redox potential of the culture medium could be used for online monitoring of the PHB production. Recovered EPS was analyzed by Fourier-transform infrared spectroscopy and subjected to gas chromatography-mass spectrometry after cleavage and derivatization steps. These analyses showed the presence of sugars which were identified as mannose, rhamnose and glucose, in a proportion near to 3.2:2.3:1, respectively. Since glycerol had not been used in previous works, these findings suggest the potential of A. cryptum to produce biopolymers from this compound at a large scale with a low risk of microbial contamination due to the low pH of the fermentation process.

Acidophilic heterotrophs: basic aspects and technological applications

“…Several strains of Acidiphilium cryptum can accumulate P3HB (Xu et al, 2013;González et al, 2023) while EPS production has also been reported for Acidiphilium sp. (Tapia et al, 2009(Tapia et al, , 2011González et al, 2023). The section below addresses how these aspects may be involved in biotechnological applications of these microorganisms.…”

“…PHAs are biopolyesters accumulated by numerous microorganisms as storage compounds, being poly (3-hydroxybutyrate) (P3HB) the most common type of PHA (Palmeiro-Sánchez et al, 2022). Several strains of Acidiphilium cryptum can accumulate P3HB (Xu et al, 2013;González et al, 2023) while EPS production has also been reported for Acidiphilium sp. (Tapia et al, 2009(Tapia et al, , 2011González et al, 2023).…”

“…Acidiphilium sp. DX1-1 (Zhang et al, 2013) has been the most commonly used strain to study the accumulation of P3HB at low pH from glucose, although the type strain A. cryptum Lhet 2 was utilized in a recent study using glycerol (González et al, 2023). The optimal conditions for P3HB production (glucose 40 g/L, KNO 3 15 g/L, and pH 3.0) were determined through an orthogonal array test which yielded the maximum of 19.75 g/L of P3HB (Xu et al, 2008).…”

“…Acidiphilium sp. also produces bound EPS mainly consisting of proteins and carbohydrates where Fe(III) can be sorbed (Tapia et al, 2009(Tapia et al, , 2011, whereas A. cryptum Lhet 2 generates soluble EPS which analysis showed the presence of mannose, rhamnose, and glucose in a proportion near to 3.2:2.3:1 (González et al, 2023).…”