Plant growth-promoting abilities and community structure of culturable endophytic bacteria from the fruit of an invasive plant Xanthium italicum

Abstract

Diversity of endophytic bacterial communities of capsular fruit, upper and lower seeds of an invasive plant Xanthium italicum growing in Xinjiang, China, was investigated. All isolates from the seed capsules, the upper seeds, and the lower seeds were identified by 16S rRNA gene sequencing, and sequences were compared to bacterial databases to define operational taxonomic units (OTUs). Finally, we obtained 316 endophytic isolates corresponding to 58 OTUs based on 16S rRNA gene sequences. The most common OTU corresponded most closely to Bacillus zhangzhouensis and comprised 9.49% of all bacterial isolates. The richness and diversity of endophytes in lower seeds were higher than that of the upper seeds; moreover, the Chao estimator and Shannon index of endophytes in the lower seeds were approximate to that in the seed capsules. Bacillus and Staphylococcus were found as the common taxa in three different tissues that were investigated (OTUs belong to these genera constituted > 70% of the total community). The bacterial endophytic communities differed significantly among these three fruit tissues, especially Bacillus strains, which have been reported to contribute to plant growth promotion and stress resilience to their hosts in harsh environment; abundance of Bacillus species was in the following order: capsules (78 OTUs) > lower seeds (55 OTUs) > upper seeds (40 OTUs). The lower seeds harboring more Bacillus species might be responsible for their earlier seed germination compared with the upper seeds.

Keywords: Community structure; Diversity; Endophytes; Heteromorphism seed; Xanthium italicum.

Fig. 1

Seed heteromorphism of X. italicum; a X. italicum fruit b the portion of the upper and lower seeds enclosed in the capsule; c comparison of the size of the upper and lower seeds

Fig. 2

A Venn diagram displaying the number of unique and shared OTUs among different tissues of X. italicum fruits. 26 of OTUs were isolated from all tissue types whereas 1 of OTUs was isolated only from the upper seed. See Table 2 for a description of OTUs. Each family was shown in a different color, that is, OTUs belonging to the same family were marked in the same color

Fig. 3

The length of Xanthium italicum seedlings infected by 30 strains compared to the control. The errors bars and letters over bars represent standard errors and significant differences at p < 0.05 based on Duncan's multiple range test

Fig. 4

The percentage of plant growth promotion of 30 strains compared with the control

Fig. 5

The biomass of Xanthium italicum plants infected by 30 strains compared to the control. The errors bars and letters over bars represent standard errors and significant differences at p < 0.05 based on Duncan's multiple range test

Fig. 6

Percentage of plant biomass promoted by 30 strains compared to the control