Differential sensitivity to infections and antimicrobial peptide-mediated immune response in four silkworm strains with different geographical origin

Abstract

The domesticated silkworm Bombyx mori has an innate immune system, whose main effectors are the antimicrobial peptides (AMPs). Silkworm strains are commonly grouped into four geographical types (Japanese, Chinese, European and Tropical) and are generally characterised by a variable susceptibility to infections. To clarify the genetic and molecular mechanisms on which the different responses to infections are based, we exposed one silkworm strain for each geographical area to oral infections with the silkworm pathogens Enterococcus mundtii or Serratia marcescens. We detected a differential susceptibility to both bacteria, with the European strain displaying the lowest sensitivity to E. mundtii and the Indian one to S. marcescens. We found that all the strains were able to activate the AMP response against E. mundtii. However, the highest tolerance of the European strain appeared to be related to the specific composition of its AMP cocktail, containing more effective variants such as a peculiar Cecropin B6 isoform. The resistance of the Indian strain to S. marcescens seemed to be associated with its prompt capability to activate the systemic transcription of AMPs. These data suggest that B. mori strains with distinct genetic backgrounds employ different strategies to counteract bacterial infections, whose efficacy appears to be pathogen-dependent.

Mechanical Processing of Hermetia illucens Larvae and Bombyx mori Pupae Produces Oils with Antimicrobial Activity

“…Insects oils are rich in other putative antimicrobials such as antimicrobial peptides (AMP), polymers, and chemical complexes that could act alone or synergically with fatty acids [ 34 , 35 , 52 , 53 ]. A recent “in silico” transcriptomic analysis of H. illucens brought to the identification of 57 peptides with putative antimicrobial activity and belonging to cecropin and defensin families [ 54 ]; on the other hand, six families of AMP have been identified in B. mori , namely cecropin, defensin, moricin, gloverin, attacin, and lebocin [ 55 ].…”

Insect Cecropins, Antimicrobial Peptides with Potential Therapeutic Applications

“…In the absence of any infections, Cec genes can be constitutively expressed at low levels in different body compartments, as demonstrated in the Drosophila reproductive tract [82] or in the silkworm B. mori midgut or fat body (a structure equivalent to the mammalian liver) [83]. Following an immune challenge, Cecs become highly transcribed in several tissues, such as gut epithelia or epidermis during local infections, and the fat body and hemocytes, during systemic infections (e.g., [51,82,83]). Like other AMPs, Cecs are translated as immature pre-peptides, undergo proteolytic cleavage of the N-terminal signal peptide, and are secreted in a mature and active form [5,7].…”

A Silkworm Infection Model for In Vivo Study of Glycopeptide Antibiotics

“…They play an essential role in those organisms that base their defense only on innate immune response, such as insects [35]. In the silkworm, mRNA synthesis of several AMPs, as cecropins, is highly upregulated as soon as the larvae undergo bacterial infection [36]. Herein, we monitored mRNA transcription of BmCECE and BmCECB1 genes coding for silkworm cecropins, which are reported to be active against Gram-positive and Gram-negative bacteria [35].…”