Degradation of formaldehyde at high concentrations by phenol-adapted Ralstonia eutropha closely related to pink-pigmented facultative methylotrophs

Abstract

The ability of the phenol-adapted Ralstonia eutropha to utilize formaldehyde (FD) as the sole source of carbon and energy was studied. Adaptation to FD was accomplished by substituting FD for glucose in a stepwise manner. The bacterium in the liquid test culture could tolerate concentrations of FD up to 900 mg L⁻¹. Degradation of FD was complete in 528 h at 30°C with shaking at 150 rpm (r = 1.67 mg L⁻¹ h⁻¹), q = 0.035 g_FD g_cell ⁻¹ h⁻¹. Substrate inhibition kinetics (Haldane and Luong equations) are used to describe the experimental data. At non-inhibitory concentrations of FD, the Monod equation was used. According to the Luong model, the values of the maximum specific growth rate (μ_max), half-saturation coefficient (k_S), the maximum allowable formaldehyde concentration (S_m), and the shape factor (n) were 0.117 h⁻¹, 47.6 mg L⁻¹, 900 mg L⁻¹, and 2.2, respectively. The growth response of the test bacterium to consecutive FD feedings was examined, and the FD-adapted R. eutropha cells were able to degrade 1000 mg L⁻¹ FD in 150 h through 4 cycles of FD feeds. During FD degradation, formic acid metabolite was formed. Assimilation of FD, methanol, formic acid, and oxalate by the test bacterium was accompanied by the formation of a pink pigment. The carotenoid nature of the cellular pigment has been confirmed and the test bacterium appeared to be closely related to pink-pigmented facultative methylotrophs (PPFM). The extent of harm to soil exposed to biotreated wastewaters containing FD may be moderated due to the association between methylotrophic/oxalotrophic bacteria and plants.

Keywords:

• Ralstonia eutropha
• formaldehyde biodegradation
• pink pigmented facultative methylotrophs
• substrate inhibition models
• oxalate degrader.

Acknowledgments

The authors are very grateful to Dr. Azadeh Mogharei, assistant professor in department of chemical engineering at AUT, and Alireza Monazzami (PhD student).