Psychrotolerant Mesorhizobium sp. Isolated from Temperate and Cold Desert Regions Solubilizes Potassium and Produces Multiple Plant Growth Promoting Metabolites.

Zahoor Ahmad Baba,R Z Sayyed,Ali Tan Kee Zuan,Tahir Ahmad Sheikh,Saad H Alotaibi,Basharat Hamid,Mohammad Javed Ansari,Hesham A El Enshasy

doi:10.3390/molecules26195758

Abstract

Soil potassium (K) supplement depends intensively on the application of chemical fertilizers, which have substantial harmful environmental effects. However, some bacteria can act as inoculants by converting unavailable and insoluble K forms into plant-accessible forms. Such bacteria are an eco-friendly approach for enhancing plant K absorption and consequently reducing utilization of chemical fertilization. Therefore, the present research was undertaken to isolate, screen, and characterize the K solubilizing bacteria (KSB) from the rhizosphere soils of northern India. Overall, 110 strains were isolated, but only 13 isolates showed significant K solubilizing ability by forming a halo zone on solid media. They were further screened for K solubilizing activity at 0 °C, 1 °C, 3 °C, 5 °C, 7 °C, 15 °C, and 20 °C for 5, 10, and 20 days. All the bacterial isolates showed mineral K solubilization activity at these different temperatures. However, the content of K solubilization increased with the upsurge in temperature and period of incubation. The isolate KSB (Grz) showed the highest K solubilization index of 462.28% after 48 h of incubation at 20 °C. The maximum of 23.38 µg K/mL broth was solubilized by the isolate KSB (Grz) at 20 °C after 20 days of incubation. Based on morphological, biochemical, and molecular characterization (through the 16S rDNA approach), the isolate KSB (Grz) was identified as Mesorhizobium sp. The majority of the strains produced HCN and ammonia. The maximum indole acetic acid (IAA) (31.54 µM/mL) and cellulase (390 µM/mL) were produced by the isolate KSB (Grz). In contrast, the highest protease (525.12 µM/mL) and chitinase (5.20 µM/mL) activities were shown by standard strain Bacillus mucilaginosus and KSB (Gmr) isolate, respectively.

Highlights

Potassium (K) is one of the main macronutrients and the most abundant cation in higher plants [1], with significant absorption that plays a vital role in metabolic activity, activation of ~80 enzymes, starch synthesis, sugar degradation, photosynthesis, disease resistance, etc. [2,3]
From the different soil samples collected from the Ladakh region and Kashmir valley, 110 morphologically different bacteria were isolated
The results of the present study showed that out of a total 110 bacterial isolates, only 13 bacterial isolates showed the ability of potassium solubilization at lower temperature conditions (0 °C, 1 °C, 3 °C, 5 °C, 7 °C, 15 °C and 20 °C) under in-vitro conditions

Summary

Introduction

Potassium (K) is one of the main macronutrients and the most abundant cation in higher plants [1], with significant absorption that plays a vital role in metabolic activity, activation of ~80 enzymes, starch synthesis, sugar degradation, photosynthesis, disease resistance, etc. [2,3]. 10% of the soil K consists of the interlayer of the non-expanded form of K-bearing minerals, such as illite, mica, and feldspar [7,8]. The majority of the K required by plants must be transported in the soil to the roots [14], and the movement of K ions is a significant element in the supply of K. This transport happens mostly in soil fluid, the liquid phase of the soil, by mass flow (with the water going to the roots of a plant) and diffusion through the concentration gradient created by the absorbent surface, i.e., roots. Hydrous mica clays have been found to fix huge quantities of K, which could not be released even with boiling HNO3 [8]

Methods

Results

Conclusion