Screening and characterization of endophytic Bacillusand Paenibacillus strains from medicinal plant Lonicerajaponica for use as potential plant growth promoters

摘要

A total of 48 endophytic bacteria were isolated from surface-sterilized tissues of the medicinal plant Lonicera japonica, which is grown in eastern China; six strains were selected for further study based on their potential ability to promote plant growth in vitro (siderophore and indoleacetic acid production). The bacteria were characterized by phylogenetically analyzing their 16S rRNA gene similarity, by examining their effect on the mycelial development of pathogenic fungi, by testing their potential plant growth-promoting characteristics, and by measuring wheat growth parameters after inoculation. Results showed that the number of endophytic bacteria in L. japonica varied among different tissues, but it remained relatively stable in the same tissues from four different plantation locations. Among the three endophytic strains, strains 122 and 124 both had high siderophore production, with the latter showing the highest phosphate solubilization activity (45.6 mg/L) and aminocyclopropane-1-carboxylic acid deaminase activity (47.3 nmol/mg/h). Strain 170 had the highest indoleacetic acid (IAA) production (49.2 mg/L) and cellulase and pectinase activities. After inoculation, most of the six selected isolates showed a strong capacity to promote wheat growth. Compared with the controls, the increase in the shoot length, root length, freshweight, dry weight, and chlorophyll content was most remarkable in wheat seedlingsinoculated with strain 130. The positive correlation between enzyme (cellulose andpectinase) activity and inhibition rate on Fusarium oxysporum, theIAA production, and the root length of wheat seedlings inoculated with each testedendophytic strain was significant in regression analysis. Deformity of pathogenicfungal mycelia was observed under a microscope after the interaction with theendophytic isolates. Such deformity may be directly related to the production ofhydrolytic bacterial enzymes (cellulose and pectinase). The six endophytic bacterialstrains were identified to be Paenibacillus andBacillus strains based on the results of 16S rRNA gene sequencinganalysis and their physiological and biochemical characteristics. Results indicatethe promising application of endophytic bacteria to the biological control ofpathogenic fungi and the improvement of wheat crop growth.