Effect of UVB radiation on morphological, physiological and biochemical changes in methylotrophs.

Phyllosphere-associated microorganisms must deal with various abiotic stresses such as high-low temperature, low nutrients, and ultraviolet (UV) radiation. These collective actions may trigger the generation of reactive oxygen species (ROS) and causes cellular damage. Cellular defense mechanisms such as morphological changes (size or appearance), production of photo-protectant compounds, and enhancement of antioxidant activities, all of which may contribute to the suppression of ROS and significantly increase survival rates under UV radiation. In this study, five UVB-resistant plant growth-promoting methylotrophs (Methylorubrum thiocyanatum (SD2), Rhodococcus kroppenstedtii (UK3), Methylorubrum populi (KD5), and Methylobacterium brachiatum (KD1 and SD3)) were investigated as adaptive strategies against UVB radiation. Exposure to UVB radiation revealed that methylotrophs changed their morphology to club or dumbbell shapes, and formed biofilm-like structures. Furthermore, Fourier transform-infrared spectroscopy (FTIR) and Gas chromatography-mass spectroscopy (GC–MS) analyses of the methanol-based intracellular extracts of methylotrophs revealed the presence of carotenoids, flavonoids, fatty acids, and antioxidants. Additionally, methylotrophs showed enhanced antioxidant activities such as superoxide dismutase, peroxidase, phenylalanine ammonia-lyase, and proline content with increased UVB exposure (1 -4 h). These findings demonstrate the ability and various adaptation strategies of methylotrophs to survive UVB exposure. These adaptive strategies may be one reason for the promotion of plant growth by methylotrophs under UVB radiation. [ABSTRACT FROM AUTHOR]