Aim The aim of this study was to evaluate the ability of Bacillus methylotrophicus M4-1 to protect winter wheat from the harmful effects of soil salinity and alkalinity. Methods and Results We isolated the halotolerant B. methylotrophicus M4-1. Two representative soils with different salt contents (S1, 213 mu s cm(-1); S2, 786 mu s cm(-1)) in the Yellow River delta region of China were selected for experiments. The effects of the M4-1 strain on the typical wheat variety (Jimai 21) in this environment were proven. In S1 soil, the M4-1 strain reduced the wheat rhizosphere soil pH (1 center dot 61%) and electrical conductivity (EC) (8 center dot 01%) and increased the exchangeable K content (11 center dot 14%). The uptake of Mg2+ (20 center dot 73%) by wheat roots and K+ (8 center dot 84%) by leaves was increased, and the content of Na+ (23 center dot 62%) in leaves was reduced. In S2 soil, the M4-1 strain was able to reduce soil EC (2 center dot 56%) and increase exchangeable K (11 center dot 20%) content. The absorption of K+ (13 center dot 28%) in wheat leaves was increased, and the content of Na+ (12 center dot 41%) in roots was decreased. Total N and organic matter contents in rhizosphere soil were significantly positively correlated with wheat growth and salt tolerance, whereas EC showed a significant negative correlation. Conclusions M4-1 attenuates salt stress injury in wheat under both low and high salt stress. Significance and Impact of the Study We demonstrated the efficacy and value of plant growth-promoting rhizobacteria addition to protect winter wheat against salt stress and improve crop yield. We also elucidated the physicochemical and biochemical interactions among M4-1, the rhizosphere and the host plant.