Phylogenetic characterization of bacterial endophytes from four Pinus species and their nematicidal activity against the pine wood nematode.

Recently, bacterial endophytes (BEs) have gained importance in the agricultural sector for their use as biocontrol agents to manage plant pathogens. Outbreak of the pine wilt disease (PWD) in Korea has led researchers to test the feasibility of BEs in controlling the pine wood nematode (PWN) Bursaphelenchus xylophilus. In this study, we have reported the diversity and biocontrol activity of BEs against the PWN. By employing a culture-dependent approach, 1,622 BEs were isolated from the needle, stem, and root tissues of P. densiflora, P. rigida, P. thunbergii, and P. koraiensis across 18 sampling sites in Korea. We classified 389 members based on 16S rDNA analysis and taxonomic binning, of which, 215 operational taxonomic units (OTUs) were determined. Using Shannon's indices, diversity across the Pinus species and tissues was estimated to reveal the composition of BEs and their tissue-specific preferences. When their ethyl acetate crude extracts were analysed for biocontrol activity, 44 candidates with nematicidal activity were obtained. Among these, Stenotrophomonas and Bacillus sp. exhibited significant inhibitory activity against PWN during their developmental stages. Altogether, our study furnishes a basic comprehension of bacterial communities found in the Pinus species and highlights the potential of BEs as biocontrol agents to combat PWD.

Genomic Insights into Nematicidal Activity of a Bacterial Endophyte, Raoultella ornithinolytica MG against Pine Wilt Nematode.

Pine wilt disease, caused by the nematode Bursaphelenchus xylophilus, is one of the most devastating conifer diseases decimating several species of pine trees on a global scale. Here, we report the draft genome of Raoultella ornithinolytica MG, which is isolated from mountain-cultivated ginseng plant as an bacterial endophyte and shows nematicidal activity against B. xylophilus. Our analysis of R. ornithinolytica MG genome showed that it possesses many genes encoding potential nematicidal factors in addition to some secondary metabolite biosynthetic gene clusters that may contribute to the observed nematicidal activity of the strain. Furthermore, the genome was lacking key components of avermectin gene cluster, suggesting that nematicidal activity of the bacterium is not likely due to the famous anthelmintic agent of wide-spread use, avermectin. This genomic information of R. ornithinolytica will provide basis for identification and engineering of genes and their products toward control of pine wilt disease.

Publisher Correction: Composition, diversity and bioactivity of culturable bacterial endophytes in mountain-cultivated ginseng in Korea.

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Characterization of gibberellin biosynthetic gene cluster from Fusarium proliferatum.

Gibberellins (GAs) are a group of phytohormones that control many developmental processes in higher plants. We report the cloning and expression pattern of gibberellin biosynthesis genes from a new GA-producing fungus, Fusarium proliferatum (strain KGL0401). These genes sequences are deposited in the National Center for Biotechnology Information (NCBI) under accession numbers EF119831, EF119832, DQ313173, DQ313174, DQ313175, DQ313176, and DQ313177. The expression level of these genes was maximal at a 0.5 M : 0.17 M carbon : nitrogen ratio, and minimal at a 0.25 M : 0.47 M carbon : nitrogen ratio.

Identification and characterization of a novel cold-adapted esterase from a metagenomic library of mountain soil.

A novel lipolytic enzyme was isolated from a metagenomic library after demonstration of lipolytic activity on an LB agar plate containing 1% (w/v) tributyrin. A novel esterase gene (estIM1), encoding a lipolytic enzyme (EstIM1), was cloned using a shotgun method from a pFosEstIM1 clone of the metagenomic library, and the enzyme was characterized. The estIM1 gene had an open reading frame (ORF) of 936 base pairs and encoded a protein of 311 amino acids with a molecular mass 34 kDa and a pI value of 4.32. The deduced amino acid sequence was 62% identical to that of an esterase from an uncultured bacterium (ABQ11271). The amino acid sequence indicated that EstIM1 was a member of the family IV of lipolytic enzymes, all of which contain a GDSAG motif shared with similar enzymes of lactic acid microorganisms. EstIM1 was active over a temperature range of 1-50°C, at alkaline pH. The activation energy for hydrolysis of p-nitrophenyl propionate was 1.04 kcal/mol, within a temperature range of 1-40°C. The activity of EstIM1 was about 60% of maximal even at 1°C, suggesting that EstIM1 is efficiently cold-adapted. Further characterization of this cold-adapted enzyme indicated that the esterase may be very valuable in industrial applications.