ABSTRACT
Serratia marcescens strain JPP1 was isolated from peanut hulls in Huai'an city, Jiangsu Province, China. Its potential to inhibit the mycelial growth of Aspergillus parasiticus and the subsequent aflatoxin production was evaluated. The strain JPP1 could produce chitinase to degrade fungal cell walls, which was the main mechanism of strain JPP1 for biocontrol. Scanning electron microscopy of fungi treated with the crude chitinase revealed abnormal morphological changes. While the strain was grown in the peanut hulls-based medium, the chitinase activity reached 7.39 units. RT-PCR analysis showed that the crude chitinase repressed the transcription of genes involved in the aflatoxin gene cluster, such as aflR, aflC (pksL1), and aflO (dmtA) genes. By visual agar plate assay and tip culture method, the strain JPP1 exhibited remarkable inhibitory effect on mycelia growth (antifungal ratio >95%) and subsequent aflatoxin production (antiaflatoxigenic ratio >98%). An in vitro assay with seed coating agent of bacterial suspension showed that strain JPP1 effectively reduced fungal growth and subsequent aflatoxin production on peanut seeds, and its antagonistic effect was superior to the common agricultural fungicide of carbendazim. These characteristics suggest that S. marcescens JPP1 strain could potentially be utilized for the biological control of phytopathogenic fungi and aflatoxin in Chinese peanut main producing areas.
Subject(s)
Aflatoxins/metabolism , Aspergillus/physiology , Chitin/metabolism , Serratia marcescens/physiology , Antifungal Agents/pharmacology , Aspergillus/drug effects , Aspergillus/genetics , Base Sequence , Chitinases/metabolism , Gene Expression Regulation, Fungal , Genes, Fungal/genetics , Mycelium/drug effects , Mycelium/growth & development , Mycelium/ultrastructure , Pest Control, Biological , Phylogeny , RNA, Ribosomal, 16S/genetics , Serratia marcescens/drug effects , Serratia marcescens/genetics , Serratia marcescens/ultrastructureABSTRACT
A total of 72 isolates of root-associated/endophytic (RAE) bacteria were isolated from peanut plants grown in the main producing areas of 6 provinces in China. The 16S rRNA gene sequences of these isolates were determined and phylogenetic analyses revealed that 72 isolates belonged to the classes Bacilli (49 isolates) and Gammaproteobacteria (23 isolates). The majority of RAE bacteria in Bacilli belonged to 2 genera, Bacillus and Lysinibacillus (48 and 1) while those in Gammaproteobacteria belonged to the genera Enterobacter, Serratia, Stenotrophomonas, and Pseudomonas (7, 11, 3 and 2 isolates, respectively). This is the first report of Lysinibacillus xylanilyticus isolate as biocontrol agent against AFs. All of the selected RAE bacteria showed inhibitory activities against Aspergillus parasiticus (A. parasiticus) growth and/or aflatoxins (AFs) production by visual agar plate assay and tip culture method. Most of the RAE bacteria strains (96 % strains) were determined to have decreased mycelia growth or AFs production levels by >50 % (p < 0.05). Bacterial isolates were further characterized for chitinolytic activity and 22 strains (30 % strains) of identified RAE bacteria degraded colloidal chitin on the chitin medium plate. Ten selected chitinolytic RAE bacteria were tested for antifungal activity on peanuts and most of them significantly decreased mycelial growth and AFs production levels by >90 %. These results showed a wide distribution of biological control bacteria against AFs in Chinese peanut main producing areas and the selected RAE bacteria could potentially be utilized for the biocontrol of toxicogenic fungi.
