GNOTOBIOTIC SYSTEM FOR STUDYING RHIZOSPHERE COLONIZATION BY PLANT GROWTH-PROMOTING PSEUDOMONAS BACTERIA

Citation
M. Simons et al., GNOTOBIOTIC SYSTEM FOR STUDYING RHIZOSPHERE COLONIZATION BY PLANT GROWTH-PROMOTING PSEUDOMONAS BACTERIA, Molecular plant-microbe interactions, 9(7), 1996, pp. 600-607
Citations number
38
Categorie Soggetti
Plant Sciences","Biothechnology & Applied Migrobiology",Biology
ISSN journal
08940282
Volume
9
Issue
7
Year of publication
1996
Pages
600 - 607
Database
ISI
SICI code
0894-0282(1996)9:7<600:GSFSRC>2.0.ZU;2-C
Abstract
A gnotobiotic system for studying tomato rhizosphere colonization by P seudomonas bacteria was developed. The system is based on sterile seed lings that are inoculated with one or two strains and subsequently gro wn in a sterile glass tube containing quartz sand. After 7 days of gro wth in a climate-controlled growth chamber, the number of bacteria pre sent on the root tip was analyzed. The system was optimized with respe ct to root morphology, inoculation of the seedling, and isolation of r oot tip bacteria. With this system, rhizosphere colonization on tomato , radish, wheat, and potato was analyzed. For detailed analysis of tom ato rhizosphere colonization by some representative plant growth-promo ting rhizobacteria, the colonization of known poor, moderate, and good potato root-colonizing Pseudomonas strains and of four Rhizobium stra ins was determined. All strains colonized the root tips when inoculate d as single strains. When inoculated in competition with the efficient root colonizer P. fluorescens strain WCS365, many strains were outcom peted. Mutants of Pseudomonas biocontrol bacteria lacking flagella or the O-antigen of lipopolysaccharide (LPS), which were isolated in prev ious studies and shown to be impaired in potato rhizosphere colonizati on in field soil systems, showed a reduced colonization ability in the gnotobiotic system also. The gnotobiotic system was used to screen a collection of 300 random P. fluorescens WCS365:: Tn5 mutants for colon ization-impaired mutants. Three novel mutants were found that were out competed by the wild-type strain in tomato root tip colonization but w ere not impaired in known colonization traits such as motility, amino acid auxotrophy, and presence of the O-antigenic side chain of LPS. On e strain appeared to be a thiamine auxotroph, suggesting that the root does not secrete a sufficient amount of thiamine to support growth of this strain. The other two mutants had a reduced growth rate in labor atory media, suggesting that growth rate is an important colonization factor. As the system is gnotobiotic and devoid of field-soil variable s, it can also be used to study the effects of selected biotic and abi otic factors on colonization.