وجود بكتيريا الكبريت في ترب داعمة للعرعر والبطوم تحت ظروف الجبل الأخضر-ليبيا

Abstract

The aims of this study were to determine the persistence of the sulphur oxidizing bacteria in different decomposition stages "the humus layer" and in the soils supporting the (Juniperus phoenicea L and Pistacia lentiscus L). These bushes covers ca 80%' of the Gabal AlAkhdar eco-region, Libya. In the culturing media, the impacts of the pH, salts, temperature and the production of sulfates from such bacterial isolates were also examined. The least significant difference (LSD, 5%) and Pearson correlations between the variables were done using SPSS. To achieve these aims, two sites contain the two plants were selected in the Settia area located north east of Shahat town at ca 400 masl. From each plant and Rhodoxeralfs soils, composite samples were collected from the humus layers The separation of these stages were carried out according to the morphology of the litters. Soil samples were collected at (0-10 cm) depth. The physical (texture and moisture) and chemical analysis including the total N, P, K, S and sulphates and the total counts of bacteria were done at the lab of soil microbiology, Omar Al Mukhtar University. The bacterial strain grew in the thiosulphate medium during a period of 7-10 days. At pH = 8, colonies in a pure culture were appeared white to light yellow .These chemolithoautotrophic mobile short rod cells were a gram-negative, non-endo-spore forming. Such characteristics indicate that this isolate was a Thiobacillus thioparus.The persistence of T. thioparus in the late stages and in the soils supporting the Juniperus were higher than in the Pistacia. The number of the strain in the Pistacia and Juniperus ranged between 0.15 ×104 to 58 × 104 and 0.16 ×104 to 61 × 104, 0.032 ×104 to 50 ×104 and 5.6 × 104 to 91 in the first and the second sites, respectively. Positive correlations were observed between T. thioparus counts and the P, K, SO4-2 and the total count of the bacteria. Strong negative correlation (p<0.001 and R2 of ca 25%, n=60) with EC. The correlations between total count and pH, and total S were negative of p<0.024 and 0.001, R2 of ca 20 t0 25%, n=60, respectively. The total S positively correlated with R2 of ca 25%. Total S positively correlated with the total P (p<0.001 and R2 of ca 25%. Sulfates positively correlated with EC (p<0.001, R2 of ca 25%, n=60, also it negatively correlated with total N (p<0.006, R2 of 16%, n=60. The optimum effect of temperature (25, 30, 35, 40) on the strain after 7 days of incubation was at 30 C and the minimum was 40C. the effect of For the pH, the optimum and minimum were 8 and 5 and no growth at 4. NaCl, CaCl2 and MgCl2 conc. of ( 0.1, 1, 5 g / L ) showed a detrimental effects comparing with the control the sodium thiosulphate medium Conc. of (0.1,1,2,3,4,5,6,7 g) showed optimum and minimum growth at 5g "control" and 0.1g respectively. The effect of this bacterial strain on pH and sulphate production in the thiosulphate medium after about two weeks of incubation revealed that the pH decreased from 7.8 to 6.4 and by 1.4 (17.95%). Sulfate concentration also increased from 0.03% to 0.05%. The Starkey medium on the other hand, decreased pH values from 7.8 to 4.5 by 3.3 (42.31%) with an increase of 24.36% in the thiosulphate medium. This reflects the impact of the type of sulfuric compound "energy source" in increasing acidity, which confirms the superiority of sulfur element "S8" in recommending the development of this bacterial strain for the purpose of reclamation of the salt affected soils (sodic soils). It was observed that the high acidity does affect the growth of this strain but the growth of such bacterium In vivo differs than the growth In vitro "The Habitat" due to the presence of calcium carbonates ; the limestone 'the bed rock' and many other alkaline ions.