AUTHOR=Zhao Yu , Yuan Zhibo , Wang Shuang , Wang Haoyu , Chao Yanjie , Sederoff Ronald R. , Sederoff Heike , Yan He , Pan Jialiang , Peng Mu , Wu Di , Borriss Rainer , Niu Ben 

TITLE=Gene sdaB Is Involved in the Nematocidal Activity of Enterobacter ludwigii AA4 Against the Pine Wood Nematode Bursaphelenchus xylophilus

JOURNAL=Frontiers in Microbiology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2022.870519

DOI=10.3389/fmicb.2022.870519

ISSN=1664-302X

ABSTRACT=<p><italic>Bursaphelenchus xylophilus</italic>, a plant parasitic nematode, is the causal agent of pine wilt, a devastating forest tree disease. Essentially, no efficient methods for controlling <italic>B. xylophilus</italic> and pine wilt disease have yet been developed. <italic>Enterobacter ludwigii</italic> AA4, isolated from the root of maize, has powerful nematocidal activity against <italic>B. xylophilus</italic> in a new <italic>in vitro</italic> dye exclusion test. The corrected mortality of the <italic>B. xylophilus</italic> treated by <italic>E. ludwigii</italic> AA4 or its cell extract reached 98.3 and 98.6%, respectively. Morphological changes in <italic>B. xylophilus</italic> treated with a cell extract from strain AA4 suggested that the death of <italic>B. xylophilus</italic> might be caused by an increased number of vacuoles in non-apoptotic cell death and the damage to tissues of the nematodes. In a greenhouse test, the disease index of the seedlings of Scots pine (<italic>Pinus sylvestris</italic>) treated with the cells of strain AA4 plus <italic>B. xylophilus</italic> or those treated by AA4 cell extract plus <italic>B. xylophilus</italic> was 38.2 and 30.3, respectively, was significantly lower than 92.5 in the control plants treated with distilled water and <italic>B. xylophilus</italic>. We created a <italic>sdaB</italic> gene knockout in strain AA4 by deleting the gene that was putatively encoding the beta-subunit of <sc>L</sc>-serine dehydratase through Red homologous recombination. The nematocidal and disease-suppressing activities of the knockout strain were remarkably impaired. Finally, we revealed a robust colonization of <italic>P. sylvestris</italic> seedling needles by <italic>E. ludwigii</italic> AA4, which is supposed to contribute to the disease-controlling efficacy of strain AA4. Therefore, <italic>E. ludwigii</italic> AA4 has significant potential to serve as an agent for the biological control of pine wilt disease caused by <italic>B. xylophilus</italic>.</p>