characterization of bacterial endophytes of sweet potatos

REGULAR ARTICLE Characterization of bacterial endophytes of sweet potato plants Zareen Khan & Sharon L. Doty Received: 21 July 2008 /Accepted: 22 January 2009 / Published online: 6 February 2009 # Springer Science + Business Media B.V. 2009 Abstract Endo phyt ic bact eria ass ocia ted with swee t potato plants ( Ipomoea batat as (L.) Lam. ) were isol ated , iden tif ied and tested for their abil ity to fix nitrogen, produce indole acetic acid (IAA), and exhibit stress tole rance. Elev en dif fere nt stra ins belo ngin g to the gene ra, Enter obacter , Rahnella, Rhodanoba cter , Pseudomonas, Stenotr ophomona s, Xanthomona s and Phyllobacterium, wer e ident ifi ed. Four st ra ins we re shown to produce IAA (a plant growth hormone) and one strain showed the ability to grow in nitrogen free medium and had the nitrogenase subunit gene, nifH . To dete rmi ne if IAA product ion by the endo phyt es had any role in pr otecting the cells against adverse conditions, different stress tests were conducted. The IAA produc er grew we ll in the pres ence of some antibiotics , UV and cold treatmen ts but the response to pH, osmotic shock, thermal and oxidative treatments was the same for both the IAA producer and the no IAA producer. To determine if IAA produced by the strains was biologically relevant to plants, cuttings of poplar were inoculated with the highest IAA producing strain. The inoculated cuttings produced roots sooner and gr ew more ra pid ly tha n uni nocul at ed cut tin gs. These studies indicate that endophytes of sweet potato plants are beneficial to plant growth. Keywords Ipomoe a batatas . Swe et pot ato . Plant-microbe intera ction . Indole ace tic aci d (IAA) . Nitro gen fixatio n . Stress . Pla nt gro wth pro moti on Introduction Endophy tes are microo rganis ms that reside within the inner part s of pl ants wi thout causing any di sease symptoms (Ha llmann et al. 1997). Cultivable endoph yti c communiti es can be iso lat ed af ter surf ace ste ril izat ion of the plan t material. Endophytes exist in a ra nge of ti ss ue types wi thi n a br oad ra nge of plants, colonizing the plant systemically with bacterial colonie s and biofilms, resid ing latently in interc ellular spaces, insid e the vascula r tissue or wit hi n cells (Ulr ich et al . 2008). Alt hough the plan t-e ndophyt e interaction has not been fully understood, it has been reported that many isolates provide beneficial effects to their hosts like preventing disease development by synthesizing novel compounds and antifungal metab- olit es. Inve sti gati ons of biodive rsi ty of endoph yte strains for novel metabolites may identify new drugs for the treatment of human, plant and animal diseases (Strobel et al. 2004). Several bacterial endophytes have bee n sh own to su ppor t pl an t growth an d increase nutrient uptake by providing phytohormo nes (Jacobson et al . 1994), low mol ecular wei ght compounds (Frommel et al. 1991), enzymes (Glick et al. 1998), antimicrobial substances like antibiotics (Bangera and Thomashow 1996) and siderophores (O’Sullivan and Plant Soil (2009) 322:197 – 207 DOI 10.1007/s11 104-009-9908-1 DO09908; No of Pages 10 Responsible Editor: Jesus Mercado-Blanco. Z. Khan : S. L. Doty ( *) College of Forest Resources, University of Washington, Seattle, WA 98195-2100, USA e-mail: [email protected]

characterization of bacterial endophytes of sweet potatos

Documents