Potassium (K) is immobilized within the clay minerals, making it unavailable for plant use. Therefore, the current study aimed to (i) select isolates of purple nonsulfur bacteria that can dissolve K (K-PNSB) and (ii) evaluate the production of plant growth-promoting substances by the K-PNSB isolates. The results revealed that from in-dyked alluvial soils in hybrid maize fields, 61 K-PNSB isolates were obtained under the pH 5.50 conditions. The total dissolved K content (K_dis) by the 61 K-PNSB isolates fluctuated from 56.2 to 98.6 mg L^-1. Therein, 3 isolates, including M-Sl-09, M-So-11, and M-So-14 had K_dis of 48.1-48.8 mg L^-1 under aerobic dark condition (ADC) and 47.6-49.7 mg L^-1 under microaerobic light condition (MLC). Moreover, these three isolates can also fix nitrogen (19.1-21.5 mg L^-1 and 2.64-7.24 mg L^-1), solubilize Ca-P (44.3-46.8 mg L^-1 and 0.737-6.965 mg L^-1), produce indole-3-acetic acid (5.34-7.13 and 2.40-3.23 mg L^-1), 5-aminolevulinic acid (1.85-2.39 and 1.53-2.47 mg L^-1), siderophores (1.06-1.52 and 0.92-1.26 mg L^-1), and exopolymeric substances (18.1-18.8 and 52.0-56.0%) respectively under ADC and MLC. The bacteria were identified according to their 16S rDNA as Cereibacter sphaeroides M-Sl-09, Rhodopseudomonas thermotolerans M-So-11, and Rhodospeudomonas palustris M-So-14. These potential bacteria should be further investigated as a plant growth-promoting biofertilizer