Cellulosimicrobium funkei: A Novel Bacterium in Potassium Solubilization from Soil in Bangalore
Abstract
Potassium (K) is avery essential element needed by plants for healthy growth and good yield. Most soils have abundance of potassium underneath in rock as insoluble forms that are unavailable for plant use. This research was carried out to join in the search to unearth microorganisms from the rhizosphere soil that are able to acton the mineral containing substances, solubilizing them to release the needed soluble form of the potassium for plant use. An isolate, which was characterized and identified to be Cellulosimicrobium funkei, showed significant solubilization on feldspar (a potassium containing compound) supplemented media. It is novel for potassium solubilization. The amount of potassium released by the isolate in comparison to reference cultures varied but favourably compared with the reference cultures. In glucose amended broth, solubilization was: Cellulosimicrobium funkei 7.04mg/l, Enterobacter hormaechei 7.15 mg/land 6.91mg/lfor Aspergillus terreus. Urea supplemented broth: Cellulosimicrobium funkei 5.45mg/l, Enterobacter hormaechei 5.38mg/land Aspergillus terreus 6.33mg/l. KCl supplemented broth: Cellulosimicrobium funkei 10.23mg/l, Enterobacter hormaechei 8.05mg/land Aspergillus terreus 9.11mg/l. For temperature, the cultures solubilized best at these respective temperatures: Cellulosimicrobium funkei 27oC, Enterobacter hormaechei 35oC and Aspergillus terreus 30oC. PH was 7.5 for Cellulosimicrobium funkei, 8 for Enterobacter hormaechei and for 7.5 for Aspergillus terreus. When they were now cultured using the combination of the above parameters Cellulosimicrobium funkei, Enterobacter hormaechei and Aspergillus terreus gave a maximum yield of 7.24mg/l, 7.03mg/land 6.81mg/l of solubilized potassium respectively. This means that the isolate Cellulosimicrobium funkei yielded more solubilized potassium from feldspar than the reference cultures and could therefore be abetter potassium solubilizer.
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Introduction
Potassium (K) exists in several forms in the soil, including mineral potassium, non-exchangeable potassium and exchangeable potassium and dissolved or solution potassium (K+ ions). Plants can only directly take up solution potassium (Shanware, 2014).
Soils commonly holdover 20000 ppm of total potassium, plants can use only the exchangeable potassium on the surface of the soil particles and that dissolved in the soil water which often amounts to less than 100 ppm and comprise only 0.1 to 2% of the total potassium (George & Michael, 2002). The rest is held up in insoluble minerals such as feldspar and mica. This is further compounded by the imbalance in fertilizer application where the ratio of potassium to other minerals like phosphorus and nitrogen is very small.
Potassium (K) is a major essential macronutrient for plant growth. The concentrations of soluble potassium in the soil are usually very low and more than 90% of potassium in the soil exists in the form of insoluble rocks and silicate minerals. Potassium (K), one of the seventeen chemical elements required for plant growth and reproduction, is often referred to as “the regulator” since it is involved with over 60 different enzyme systems in plants. Besides its potential to resist drought and disease (Cakmak, 2005; Billore, et al., 2009), it helps in the production of starch, controls root growth and regulates the stomata movement in plant cells and also contributes to quality. Organic matter after decomposition produces acids like citric acid, formic acid, malic acid, oxalic acid. These organic acids produced, enhance the dissolution of potassium compounds by supplying protons and by complexing Ca2+ ions .Previous work has shown organic compounds produced by micro-organisms such as acetate, citrate and oxalate can increase mineral dissolution in soil (Sheng, 2003). Solubilization of potassium occurs by complex formation between organic acids and metal ions such as Fe2+, Al 3+ and Ca2+ (Styriakova, 2003).
In Indian soil, the soluble potassium form is present in approximately 2% and the insoluble form is present in the range of 98% inform of minerals like biotite, feldspar, mica, muscovite and vermiculite (Goldstein, 1994). This presents an apparent need to search for alternative sources of potassium for plant uptake and use as well as maintaining its availability in the soil for a sustained use. Soil microbes have been reported to playa key role in the natural potassium cycle and therefore, potassium solubilizing microorganisms present in the soil could provide an alternative technology to make potassium available for uptake by plants (Rogers et. al., 1998).
This research was therefore embarked upon to further search out such microorganisms from rhizosphere soil with capabilities of dissolving the insoluble forms of potassium compound to release the soluble potassium for plant use, healthy growth and increased yield.
Conclusion
In this study, an isolate showed zone of potassium solublization in aleksandrov medium using feldspar as the insoluble potassium source. Morphological and biochemical tests on the isolate from the rhizosphere soil that showed solubilization activity pointed to its identity as Cellulosimicrobium funkei a novel organism in potassium solubilization. Optimization tests with varying concentrations of carbon, nitrogen, potassium sources, temperature and pH showed encouraging solubilization ability by the isolate and it compared favourably and in some instances better than the
