Phospholipase A2 inhibitors in bacterial culture broth enhance pathogenicity of a fungus Nomuraea rileyi

Abstract

An entomopathogenic fungus, Nomuraea rileyi, was isolated and its identity was confirmed by its internal transcribed spacer DNA sequence. The isolated N. rileyi exhibited a specific pathogenicity to lepidopteran species. This study was focused on enhancing the fungal pathogenicity by using immunosuppressive agents. In response to infection of N. rileyi, Spodoptera exigua larvae significantly induced catalytic activity of phospholipase A(2) (PLA(2)) in three immune-associated tissues, namely hemocytes, fat body, and hemolymph plasma. Furthermore, the infected S. exigua larvae induced transcription of several antimicrobial peptide (AMP) genes. Two entomopathogenic bacteria, Xenorhabdus nematophila (Xn) and Photorhabdus temperata subsp. temperata (Ptt), possessed specific PLA(2)-inhibitory activities and their culture broths significantly inhibited the enzyme activities in hemocytes, fat body, and plasma of S. exigua. In addition, the bacterial metabolites inhibited transcription of AMP genes in S. exigua that would normally respond to the immune challenge by N. rileyi. The immunosuppressive effect of Xn or Ptt bacterial broth resulted in significant enhancement of the fungal pathogenicity against late instar larvae of S. exigua and Plutella xylostella. The effect of such a mixture was confirmed by field assay against two lepidopteran species. These results suggest that the bacterial and fungal mixture can be applied to develop a novel biopesticide to control lepidopteran species.

Thromboxane Mobilizes Insect Blood Cells to Infection Foci

“…Nonetheless, the understanding insect physiological and molecular mechanisms of host defense against invading fungi remains incomplete. Here, we contribute a new understanding of the biochemical signaling mechanisms responsible for host cellular immune responses to infections by an entomopathogen, M. rileyi, which is known to be a pathogenic fungus to S. exigua (17). Specifically, we identified two eicosanoids, the prostanoids TXA 2 and TXB 2 , as key signals responsible for hemocyte migration to infection foci, phagocytosis of fungal conidia, and hemocyte microaggregation reactions to infection.…”

“…Genomic DNA (gDNA) was extracted from a mixture of isolated spores and hyphae with phenol extraction and ethanol precipitation, as described by Park and Kim (17). Internal transcribed spacer (ITS) region was amplified using ITS forward primer (5'-TTGATTACGTCCCTGCCCTTT-3') and ITS reverse primer (5'-TTTCACTCGCCGTTACTAAGG-3') as reported by Vrain et al (30).…”

“…Various roles of PGs in immune mediation have been unraveled in selected insect species. PGs mobilize sessile hemocytes to increase the number of circulatory hemocytes in plasma in S. exigua (17). In Manduca sexta, PGs promote the migration of hemocytes to infection foci (18).…”

Repat33 Acts as a Downstream Component of Eicosanoid Signaling Pathway Mediating Immune Responses of Spodoptera exigua, a Lepidopteran Insect

“…Autographa californica multiple nucleopolyhedrosis virus (AcMNPV), a baculovirus, was cultured using Sf9 cells according to the method described by Jung and Kim [ 29 ]. Metarhizium rileyi , an entomopathogenic fungus, was isolated from infected S. exigua in a welsh onion field [ 30 ] and cultured on solid potato dextrose agar medium (5% potato extract, 0.5% dextrose, 1.7% agar) at 25 °C for 7 days. Conidia suspension was prepared by scraping the fungal culture into 0.1% Triton X−100 solution and counted using a Neubauer hemocytometer (Marienfeld-Superior, Lauda-Königshofen, Germany) under 40× magnification.…”

Characteristics and Virulence Assay of Entomopathogenic Fungus Nomuraea rileyi for the Microbial Control of Spodoptera exigua (Lepidoptera: Noctuidae)

“…(Jaramillo et al, 2005;Santos et al, 2007;Brito et al, 2008;Paula et al, 2011;Sun et al, 2012). 또한 다른 친환경 방제제인 여러 가지 친환경 추출물 또는 천적 곤충과 곰팡이 살충제를 함 께 처리함으로써 곰팡이 살충제의 낮은 살충력을 보완 하면서 동시에 두 가지 모두 살충효과를 높일 수 있는 것에 대해 많은 연 구가 활발히 이루어지고 있다 (Wekesa et al, 2007;Rashki et al, 2009;Park and Kim, 2012). 따라서 N. rileyi SDSe의 경우 에도 그 자체만으로는 충분한 살충효과를 기대하기 어렵다고 볼 때, 화학살충제나 다른 친환경 방제제와의 혼용을 통해 그 효과 를 극대화 시킬 수 있는 연구가 더욱 필요한 것으로 여겨진다.…”