An Alcaligenes strain emulates Bacillus thuringiensis producing a binary protein that kills corn rootworm through a mechanism similar to Cry34Ab1/Cry35Ab1

Abstract

Crops expressing Bacillus thuringiensis (Bt)-derived insecticidal protein genes have been commercially available for over 15 years and are providing significant value to growers. However, there remains the need for alternative insecticidal actives due to emerging insect resistance to certain Bt proteins. A screen of bacterial strains led to the discovery of a two-component insecticidal protein named AfIP-1A/1B from an Alcaligenes faecalis strain. This protein shows selectivity against coleopteran insects including western corn rootworm (WCR). Transgenic maize plants expressing AfIP-1A/1B demonstrate strong protection from rootworm injury. Surprisingly, although little sequence similarity exists to known insecticidal proteins, efficacy tests using WCR populations resistant to two different Cry proteins show that AfIP-1A/1B and mCry3A differ in their mode of action while AfIP-1A/1B and the binary Cry34Ab1/Cry35Ab1 protein share a similar mode. These findings are supported by results of competitive binding assays and the similarity of the x-ray structure of AfIP-1A to Cry34Ab1. Our work indicates that insecticidal proteins obtained from a non-Bt bacterial source can be useful for developing genetically modified crops and can function similarly to familiar proteins from Bt.

A selective insecticidal protein from Pseudomonas mosselii for corn rootworm control

“…Although the root node‐injury score is not as low as for corn producing Cry34Ab1/Cry35Ab1, PIP‐47Aa holds promise as a new tool to help combat this devastating pest. The discovery of PIP‐47Aa, along with several earlier examples (Sampson et al ., ; Schellenberger et al ., ; Yalpani et al ., ), indicates diverse bacteria other than Bt represent a potentially rich source for novel insecticidal proteins. Although the mechanism of insect toxicity of these newly discovered non‐ Bt proteins awaits further investigation, they share some characteristics with Bt proteins.…”

“…Recently, novel insecticidal proteins with activity against key crop insect pests have been identified from non-Bt microbes. These include a tiny insecticidal protein (Tip), IPD072Aa from P. chlororaphis (Schellenberger et al, 2016; Tabashnik, 2016), an insecticidal protein, GNIP1Aa, from Chromobacterium piscinae (Sampson et al, 2017), and a binary rootworm active AfIP-1A/1B, from Alcaligenes (Yalpani et al, 2017). Transgenic corn plants expressing IPD072Aa showed strong efficacy in glasshouse and field tests against WCR.…”

“…To test whether PIP-47Aa shares the same binding site(s) with Cry34Ab1/Cry35Ab1, we used AfIP-1A/1B from Alcaligenes, which shares binding sites with Cry34Ab1/Cry35Ab1 (Yalpani et al, 2017). WCR BBMVs (20 lg) were incubated with 2 nM Alexa-labelled PIP-47Aa in the binding buffer in the absence or presence of a saturating concentration of an AfIP-1A and AfIP-1B mixture (0.5 lM AfIP-1A and 2 lM AfIP-1B).…”

Susceptible and mCry3A resistant corn rootworm larvae killed by a non-hemolytic Bacillus thuringiensis Cyt1Aa mutant

“…These novel toxins do not share receptors with Cry3A or Cry34/35Ab1 and neither showed cross-resistance in Cry3A-selected insects 10,11 , while IPD072Aa also showed no cross-resistance to Cry34/35Ab1-selected insects 10 . In addition a binary toxin named AflP-1A/1B isolated from the bacteria Alcaligenes faecalis was shown to be toxic against WCR although it shares a similar mode of action as the Cry34/35Ab1 toxin since WCR population resistant to Cry34/35Ab1 showed cross-resistance to AflP-1A/1B 12 .…”

Effective bacterial insecticidal proteins against coleopteran pests: A review

“…Biocontrol measures such as the use of Bacillus thuringiensis (Bt) pesticides or genetically modified plants that express insecticidal proteins are current alternative strategies. Bacteria such as Bt, B. popilliae , B. laterosporus, Alcaligenes faecalis , Pseudomonas chlororaphis , P. mosselii , and Paenibacillus lentimorbus have been reported to express insecticidal proteins and are toxic to coleopteran pests (Bravo, Likitvivatanavong, Gill, & Soberón, ; Höfte & Whiteley, ; Jouzani, Valijanian, & Sharafi, ; Sanchis, ; Schellenberger et al, ; Wei et al, ; Yalpani, Dan, & Barry, ; Yokoyama, Tanaka, & Hasegawa, ; Zhang, Hodgman, Krieger, Schnetter, & Schairer, ). In this review, we summarized these reported coleopteran‐pest‐specific bacteria and insecticidal proteins to provide a comprehensive overview and to offer long‐term guidance for the utilize of insecticidal proteins to control coleopteran pests in the future.…”