In recent years, special attentions have been paid on microbial diversity in harsh environments. But the number of researches on extremophiles bacteria such as haloalkalophiles in the soil environments, in particular in connection with agriculture is still relatively low. Those microorganisms with beneficial activity on plant growth can be employed in agriculture. In this study, 15 halophilic, 19 alkalophilic and 14 haloalkalophilic bacterial isolates were isolated from saline and alkaline soil resources in Khorasan Razavi Province (Iran). They were purified on the Ventosa moderately halophilic, Horikoshi (I) and a specific haloalkaliphilic bacteria culture medium respectively. 3Ͳindoleacetic acid (IAA) concentration were measured by UV/VIS spectrophotometer. The results showed that the IAA concentrations produced by the halophilic isolates were different statistically (Pч0.05). The amount of IAA varied from 20.36 (H8 isolate) to 0 ppm (H4 isolate). Alkalophilic isolates (A8 and A1) produced more IAA compare to the rest of isolates. Two other alkalophilic isolates (A11 and A13) had the second rank of IAA production among the alkalophilic isolates. The A7, A2, A14, A3, A17, and A6 isolates created the lowest concentrations of IAA. The highest means of IAA concentration was observed among the haloalkalophilic strains with 21.16 ppm. It was about 14.5 and 8 times more than the 3 indoleacetic acid produced by the halophilic and alkalophilic isolates respectively. Multiple regression analysis showed that there isn't any high significant relationship Between independent variables (such as electrical conductivity and pH of culture medium) with dependent variable (IAAͲconcentration) among the isolates. The regression coefficients for halophilic, alkalophilic and haloalkalophilic bacterial strains were 0.533, 0.010 and 0.327 respectively. IAA producing extremophiles bacteria may be able to promote the plant growth under saline and alkaline stress.

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