الملخص الإنجليزي
Biotechnological solutions for environmental issues are preferred over other chemical
or physical approaches for their efficacy, eco, and environmental sustainability. The
use of sulfur-oxidizing bacteria (SOBs) as bio-inoculants has been widely proposed. It
enhances sulfur oxidation in soils, increases bioavailable soil sulfate and lessens
fertilizer application. In this project, we hypothesize that: a) Omani soils will hold a
diverse SOB community; and b) Extremophilic (halophilic, thermophilic alkaliphiles)
SOB can be isolated with potential biotechnological applications for increasing the
oxidation of the elemental S during the reclamation and management of saline-sodic
soil. The objectives of the study are, to assess the impact of elemental sulfur in the
abundance and diversity of the chemo-lithotrophic sulfur-oxidizing bacteria in soils by
16S rRNA sequencing, and to isolate and identify sulfur-oxidizing bacteria from soils
fertilized with elemental sulfur using enrichment and plating. This study also aimed to
quantify the elemental sulfur oxidation activity of isolated culturable SOB strains and
evaluate the range of temperatures, pHs and ionic strengths in which these SOB
bacteria can be cultivated, in order to assess the suitability for their inoculation in
saline soils. The GS-MS quantification of elemental sulfur showed that only a marginal
oxidation rate of elemental sulfur was observed when soil solutions' NaCl
concentrations were adjusted to over 10%. This was associated with a reduction by 89
% of sulfate release for when soil solutions NaCl concentrations, compared to when
no NaCl was added. The results from this study showed that for five different soils
from Al-Batinah, there was a significant difference in the number of SOB 16s rRNA
sequences between the soils treated with 1000 mg kg -1
and unamended control soils
(without elemental sulfur application). Moreover, the overall number of OTUs
detected increased for soils incubated with 1000 mg kg -1
elemental sulfur. From the
sulfur-treated soils, strains were isolated using different agar media selective for SOB.
Among these isolates 15 different strains with positive Maldi-biotyper identification
were selected for further screening: Achromobacter xylosoxidans S1, Bacillus
horikoshii S2, Bacillus megaterium S3, Cellulosimicrobium cellulans S4,
Enterobacter cloacae S5 and S6, Halomonas aquamarine S7, Ochrobactrum
intermedium S8, Paenibacillus amylolyticus S9, Paenibacillus glucanolyticus S10,
Paracoccus versutus S11, Pseudomonas aeruginosa S12, Pseudomonas indica S13,
Pseudomonas medosina S14 and Stenotrophomonas maltophilia S15. The highest
sequence among isolated species was in Paracoccus spp. The change of number of
sequences from these isolated from the 16 rRNA diversity analysis after sulfur
application was a 35.1% increase, showing that these strains are increased by Sulfur
application and therefore likely SOB. Furthermore, all isolated strains were able to
grow both chemoorganotrophically and chemolithotrophically. Halomonas
aquamarine S7, Enterobacter cloacae S6 and Cellulosimicrobium cellulans S4
showed the highest in vitro potential for S0 oxidation and pH reduction respectively. Halomonas aquamarine S7 was the most halophilic SOB, able to withstand the highest
NaCl dose (2M) of with cell growth of 1.40 x107 CFU ml-1after 20 h. Halomonas
aquamarine was here characterized as a halophilic and alkaliphile and was able to
oxidise sulfur to sulfate in vitro (44 mg L-1 day-1
) causing a slight reduction of media
pH up to -0.41 point. Therefore, Halomonas aquamarine S7 was the most promising
sulfur oxidizing bacteria isolated, and was selected to be tested as a inoculant for
Omani saline-sodic soils for increasing sulphur oxidation under these conditions.
Further studies are needed to test the inoculation of this bacteria, its survival and
sulphur oxidation efficiency in real Omani soil environments and conditions.
