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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 (Kdis) by the 61 K-PNSB isolates fluctuated from 56.2 to 98.6 mg L−1. Therein, three isolates, including M-Sl-09, M-So-11, and M-So-14 had Kdis 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. [ABSTRACT FROM AUTHOR]

In rice-shrimp farming systems, the high level of sodium that shrimps are able to grow in may create an adverse environment for rice. This research aimed to isolate purple nonsulfur bacteria (PNSB) from rice-shrimp fields and select strains that were resistant to H+, Al3+, Fe2+ and Mn2+, that can produce plant growth promoting substances such as 5-aminolevulinic acid, exopolymeric substances, indole-3-acetic acid and siderophores. The selected bacteria were applied in a soil pot experiment to determine their ability to enhance rice growth and yield. From 63 PNSB isolated from 21 paddy fields of rice-shrimp systems, four strains were selected for their properties as biofertilizers and plant growth promoters (PGP). They were all identified as strains of Luteovulum sphaeroides. A randomized complete block design incorporating six treatments was used to investigate the ability of the four PNSB strains to ameliorate rice growth and yield in saline acidic soil with saline water irrigation at 4‰. PNSB cultures at 1.90 × 105 CFU g−1 dry soil weight were applied three times, along with normal chemical fertilizers, and all monitored parameters of rice growth and grain yield significantly improved in soil with a toxic Al3+ content of 10.8 meq 100 g−1. A mixed four cultures most effectively increased grain yield (86.8%) compared with no applied PNSB. Remediation of the pot soil was exhibited in decreased exchangeable Na in soil and proline content in leaves. The four PNSB could act as biofertilizers, PGP and bioremediators with potential to enhance rice yield in rice-shrimp systems for sustainable rice cultivation. [ABSTRACT FROM AUTHOR]