Screening Of Bacteria Capable Of Inducing Trap Formation In A. Oligospora And Their Trap Formation Mechanism

In this study, some bacterial strains that could induce trap formation in Arthrobotrys oligospora were isolated from agricultural soil and identified by their16SrRNA sequences.Mechanism of trap formation by bacteria in A. oligospora was investigated by SEM.The bacterial strains associated with wild A. oligospora that could induce trap formation were isolated and identified by their16SrRNA.The results of the whole work were shown follows:1. Fourteen bacterial strains that could induce trap formation in A. oligospora were isolated from agricultural soil.On the basis of their16S ribosomal DNA sequences,14soil bacterial strains were identified as follows:Lysobacter sp.(one strain), Variovorax sp.(one strain), Stenotrophomonas sp.(one strain), Chryseobacterium sp.(one strain), Bacillus sp.(four strains), Sphingomonas sp.(one strain), Kocuria sp.(one strain), Pseudoxanthomonas sp.(two strains), Arthrobacter sp.(one strain), Ochrobactrum sp.(one strain). Bacterial cells were the all strains, Lysobacter, Variovorax, Stenotrophomonas and Chryseobacterium strain displayed a relatively better capability. Presence of bacterial cells was the prerequisite to the trap formation in A. oligospora and bacterial metabolites could facilitat trap formation.2. A preliminary study of the mechanism behind trap formation by Chryseobacterium sp. TFB showed that:conidia of A.oligospora produced a few mycelial traps (MT) and conidial traps (CT) when cultured with bacterial cells which they didn't produce when cultured with bacterial cell-free culture filtrate. However co-culture of A. oligospora with bacterial cells and bacteria-free filtrate simultaneously induced MT and CT in large amounts. With the increased concentration of bacteria-free filtrate, the number of typical CT increased, but conidial germination was progressively inhibited. Scanning electron microscopy of A. oligospora co-cultured with bacteria revealed that bacterial attachment to hyphae was a prerequisite to trap formation and that bacteria-free filtrate facilitated bacterial attachments to hyphae. The results that the addition of nutrients in co-culture medium decreased the number of traps suggest that this type of trap formation may be favoured at a low nutrient status.3. Eight nematode-trapping fungi tested were able to form MT and CT when cocultured with Chryseobacterium sp. TFB cells and cell-free culture filtrate, but the abilities varied among species.4. Thirty-five bacterial strains that could induce trap formation in A. oligospora were isolated from the surface of wild Hyphae of A. oligospora. On the basis of their16S ribosomal DNA sequences,35bacterial strains were identified as follows:Stenotrophomonas sp.(ten strains), Agrobacterium sp.(eight strains), Achromobacter sp.(thirteen strains), Zhihengliuella sp.(three strains), Sphingobium sp.(one strain). Presence of bacterial cells was the prerequisite to the trap formation in A. oligospora and bacterial metabolites could facilitat trap formation.5. By using SEM and FISH technology, we have ascertained the presence of ectosymbiotic bacteria belong to Agrobacterium associated to the mycelium of wild A. oligospora.In summary, this work was innovative as follows:1.Some bacterial strains could induce trap formation in A. oligospora, and bacterial attachment to hyphae was a prerequisite.2.Some bacterial strains that could induce trap formation in A. oligospora were associated with wild A. oligospora.