Characteristics and influencing factors of biofilm formation by a pyridine-degrading bacterium Pseudomonas sp. ZX08

Abstract:

[Background] The wastewater discharged by coal chemical industries contains a large number of refractory and highly toxic organic pollutants. It is an economically feasible strategy to treat the wastewater with bioaugmentation technology based on efficient degrading bacteria. Promoting the biofilm formation of degrading bacteria is proved to be beneficial to the performance of the biofilm wastewater treatment system. [Objective] To investigate the biofilm formation process and characteristics of a pyridine-degrading bacterium Pseudomonas sp. ZX08, and to identify the influence of different environmental factors such as temperature, pH, Na+, K+, Ca2+, Mg2+ on biofilm formation, and finally to provide references for regulating biofilm formation in wastewater treatment systems. [Methods] A modified microtiter dish biofilm formation assay was used to determine the biofilm formation and the planktonic bacteria growth in the 12-well plate under different conditions; the structural characteristics of biofilm was observed and analyzed by a confocal laser scanning microscope (CLSM). [Results] Pseudomonas sp. ZX08 showed good pyridine-degrading performance and biofilm-forming abilities. According to the CLSM analysis, the thickness of its biofilms formed at the surface reached 40?50 mm, and the proportion of live cells and protein/cell ratio were higher in the outer layer of the biofilms. A periodic variation was observed in the biofilm formation process in 72 h, and the biofilm biomass at 12 h and 48 h were relative peaks. The optimum temperature for ZX08 biofilm formation was 25 °C, and the optimum pH range was 7.0?9.0. Higher concentrations of NaCl (>0.6 mol/L) and KCl (>0.4 mol/L) significantly inhibited the biofilm formation of ZX08. Within a certain range (0?16 mmol/L), the increase of Ca2+ concentration could promote the biofilm formation at the solid-liquid interface of the 12-well plate bottom. Adding Mg2+ ranged from 0?16 mmol/L also resulted in a slight increase in the biofilm formation of ZX08. [Conclusion] The pyridine-degrading bacterium Pseudomonas sp. ZX08 can form thick and stable biofilms, and it needs to comprehensively consider the influence of various environmental factors on its biofilm formation in future applications.