Isolation and characterisation of sulfur-oxidising bacteria, including strains of Rhizobium, from calcareous sandy soils and their effects on nutrient uptake and growth of maize (Zea mays L.)

Four sulfur-oxidising bacteria were selected among 427 bacterial isolates from calcareous sandy soils in the United Arab Emirates (UAE). These isolates were selected based on their strong ability to oxidise elemental sulfur (S°) in vitro and were identified as Paracoccus versutus CBS 114155, Paracoccus pantotrophus CBS 114154, and 2 strains as Rhizobium spp. NCCB 100053 and NCCB 100054. This is the first published report of a Rhizobium species capable of S° oxidation and also the first record of sulfur-oxidising bacteria from UAE soils. These isolates were tested in a greenhouse in the presence and absence of S° to study their effects on maize growth. Best growth was observed in the treatment with P. versutus application combined with S°, which significantly reduced soil pH, increased soil SO₄ level and the uptake of N, S, Fe, Mn, and Zn in maize roots and shoots. The P and Cu uptake in the shoots of maize plants was not significant compared with the treatment that received the application of S° alone. There was no response in plant growth to treatments that included the application of S° combined with P. pantotrophus or Rhizobium strain NCCB 100053 compared with the treatment that received the application of S° alone. There was significant growth inhibition of maize plants in the treatment receiving Rhizobium strain NCCB 100054 with or without the application of S° compared with the treatment that included the application of S° alone. This growth inhibition was associated with a significant decrease in the levels of N, P, S, Fe, Mn, Zn, and Cu in roots and shoots in the absence of S°. Rhizobium strain NCCB 100054 applied with S° significantly decreased the levels of N, S, and Fe in the roots and the levels of N, P, S, Fe, Mn, and Cu in the shoots of maize, with no significant differences in the levels of P and Mn in the roots and in the levels of Zn in the shoots, compared with the treatment with S° alone. These results indicate that the treatment P. versutus combined with S° can be effective as a soil conditioner for horticultural production in calcareous sandy soils.