جداسازی و بررسی برخی خصوصیات محرک رشدی باکتری‌های متحمل به نمک مولد پلیمر از خاک‌های شور

نوع مقاله: مقاله پژوهشی

نویسندگان

1 دانشجوی دکتری دانشگاه غلوم کشاورزی و منابع طبیعی گرگان

2 دانشیار گروه خاک دانشگاه علوم کشاورزی و منابع طبیعی گرگان

3 استادیار گروه خاک دانشگاه علوم کشاورزی و منابع طبیعی گرگان

چکیده

گسترش شوری چالش بزرگی در بیشتر خاک‌های زراعی مناطق خشک و نیمه‌خشک می‌باشد. اخیراٌ استفاده از روش‌های زیستی همانند استفاده از ریزجانداران خاکزی به منظور کاهش اثرات زیان‌بار شوری بر گیاهان، اهمیت زیادی پیدا کرده است. در این مطالعه سعی شده است باکتری‌های متحمل به نمک از خاک‌های شور جداسازی گردند و خصوصیات محرک رشدی آنها همانند توانایی تولید اکسین، سیدروفور، سیانیدهیدروژن، مقاومت به خشکی و آزادسازی فسفر و پتاسیم از منبع نامحلول معدنی، بررسی شود. از بین 20 جدایه متحمل به نمک مولد پلیمر، بر اساس آزمون خاصیت محرک رشد گیاه، در نهایت دو جدایه شماره 17 و 5 به‌عنوان جدایه برتر انتخاب شدند. نتایج نشان داد که میانگین مقدار پلیمر از 8/0 تا 2/4 گرم بر لیتر متغیر بود و بیشترین آن در جدایه 17 به دست آمد. اکثر جدایه‌ها قادر به تولید هاله نارنجی در محیط CAS-Agar بودند که بیشترین مقدار سیدروفور در جدایه 5 با نسبت قطر هاله به کلنی برابر با دو مشاهده شد. بیشترین میزان تولید اکسین در جدایه شماره 17 با مقدار 14/8 میلی‌گرم بر لیتر مشاهده شد. همچنین این جدایه بالاترین توانایی آزادسازی پتاسیم معدنی با مقدار 2/12 و 62/18 میلی‌گرم بر لیتر به‌ترتیب در حضور و عدم حضور نمک داشت. اغلب جدایه‌ها مقاومت به خشکی در سطح 2 و 5 بار از خود نشان دادند. بیشترین مقاومت به خشکی در سطح 15بار در جدایه شماره 17 و 5 به‌ترتیب با 6/55 و 2/53 درصد کاهش رشد نسبت به محیط بدون تنش مشاهده شد. آزمایش‌های تعیین ترادف ژنی SrRNA16 نشان داد که جدایه 17 به میزان 4/99 درصد با سویهDSM13 Bacillus licheniformis و جدایه 5 به میزان57/99 درصد با سویه Bacillus megaterium NBRC 15308 قرابت فیلوژنی دارند.

کلیدواژه‌ها


عنوان مقاله [English]

Isolation and investigation of some growth-promoting properties of halotolerant bacteria -producing polymer of saline soils

چکیده [English]

Abstract
Salinity is the most important challenge in arid and semi arid regions. Recently, biological methods are considered as a way for decreasing harmful effects of salinity on plant. In this study halotolerant bacteria were isolated from saline soils. The characteristics of plant growth promotion (PGP) such as production of exopolymer, siderophore, HCN, auxin, ability of potassium and phousphate solubilization and tolerance to drought stress were investigated. Among the 20 isolates selected, two isolates (5, 17) selected as super isolates based on PGP test. Results shown that mean produced exopolymer was in range of 0.8 to 4.2 g l-1 and maximum value was observed by the isolate17. All of the isolates can produce halo in CAS-Agar and bacteria isolate No. 5 produced maximum siderophore with the halo to colony ratio two. Maximum auxin production (8.14 mg l-1) was observed by the isolate17. Also, this isolate had highest ability of potassium solubilization in presence (12.20) and absence (18.62) of salt. Most of the isolates showed drought tolerance at 2 and 5 bar levels. At 15 bar, Isolates 17 and 5 has the highest tolerance to drought stress in comparison to control with 55.6 and 53.2 percentage reuction in growth rate, respectively. With 16S rRNA sequencing, the more closley studied of halotolerant superior isolates were identified as Bacillus. Isolate No. 17 had 99.4% similarity to Bacillus licheniformis DSM13, while isolate No.5 showed 99.57% sequence homology to Bacillus megaterium NBRC 15308.

کلیدواژه‌ها [English]

  • Auxin
  • Exopolysaccharide
  • Tolerance to drought
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