ABSTRACT
As acid soils of Odisha have been facing a major constraint in phosphorus availability, application of native P solubilizing bacteria could be promising as well as ecofriendly step towards sustainable P availability for crop growth and development. To address the problem of P availability in acid soil of Bhubaneswar, Odisha, rhizosphere soil samples (pH ? 5.50) with rice – pulses (green gram/black gram) cropping system were collected and phosphate solubilising bacteria were isolated. In vitro characterization of the PSB isolates were conducted with calcium, aluminium and iron phosphates to recover soluble P. All the five strains i.e. Bacillus cereus BLS18 (KT582541), Bacillus amyloliquefaciens CTC12 (KT633845), Burkholderia cepacia KHD08 (KT717633), Burkholderia cepacia KJR03 (KT717634), Burkholderia cepacia K1 (KM030037) could solubilize Ca3(PO4)2, AlPO4, FePO4, and Fe3(PO4)2. Higher recovery of soluble P was with Ca3(PO4)2 while the least was with AlPO4. All the strains exibited a trend similar with respect to P recovery i.e. Ca3(PO4)2 > FePO4 > AlPO4 > Fe3(PO4)2. B. amyloliquefaciens CTC12 was most efficient in solubilizing calcium and iron phosphates whereas B. cepacia KHD08 recovered maximum P with aluminium phosphate. All the inorganic salt fortified mediums showed a significant decline in pH which necessitated the identification of compounds present in the mediums. Organic acids viz; acetic, citric, gluconic, lactic, malic, succinic, tartaric acids in the mediums were identified by HPLC. Tartaric acid was only found in the mediums supplemented with AlPO4. B. amyloliquefaciens CTC12 and B. cepacia KHD08 showed promising results in in vitro analysis of P solubilization. The present study is focused on problematic acid soils where phosphorous is unavailable and mostly fixed with aluminium and iron ultimately making it unavailable for the crops to take up. This leads to unbalanced and frequent use of chemical fertilizer. Hence the study is a significant attempt to characterize native PSBs with capacity to solubilize Al-P and Fe-P
ABSTRACT
Experiments were conducted in two phases, first under in vitro condition to study the stress tolerant ability and then in pot experiment to study the effect of Rhizobium isolates on rhizospheric microbial activity. The strain CHRS-7 could tolerate the pH 4.0, whereas RAN-1 and RAB-1 could not. The growth of all the strains was luxuriant in 1% NaCl solution and decreased with increase in the concentration of NaCl. All the strains could produce the phytohormone indole acetic acid (IAA) by metabolizing different carbon sources. The highest amount of IAA was produced by RAB-1 (81 µg/mL), CHRS-7 (78 µg/mL) and RAN-1 (72 µg/mL) by metabolizing mannitol, glucose , and sucrose, respectively. The higher bacteria and rhizobial population was enumerated in the treatment with inoculation of Rhizobium strains and added with 50% of soil test dose of nitrogen whereas higher fungi population was enumerated with the treatment receiving 150% of a soil test dose of nitrogen. The soil enzymes activity, microbial biomass carbon and nitrogen were also higher with a lower dose of external sources of N (50% of a soil test dose) and decreased with increase in nitrogen dose.
ABSTRACT
Three bacterial strains CHRS-7, RAB-1 and RAN-1 were isolated from root nodules of redgram (Cajanus cajan) and identified as Rhizobium sp. based on 16S rDNA sequence homology and assigned accession number MH636329, MH636773 and MH541051, respectively by National Center for Biotechnology Information (NCBI). All the strains could produce copious amount of exopolysaccharides in yeast extract manitol broth medium. All the three strains had different stationary phases but the bacterial growth and exopolysaccharides production occurred simultaneously. The glucose (1.5 %), manitol (2.0%) and sucrose (1.5%) were the preferable carbon sources of CHRS-7, RAB-1 and RAN-1 respectively, for both growth and EPS production. Among the nitrogen sources glycine (0.1%), NaNO3 (0.1%) and KNO3 (0.1%) were the preferable N sources for CHRS-7, RAB-1 and RAN-1 respectively, whereas, CHRS-7, RAB-1 and RAN-1 preferred biotin 1.5%, 2.0% and 1%, respectively.