Gut microbiota promotes host resistance to low-temperature stress by stimulating its arginine and proline metabolism pathway in adult Bactrocera dorsalis

Abstract

Gut symbiotic bacteria have a substantial impact on host physiology and ecology. However, the contribution of gut microbes to host fitness during long-term low-temperature stress is still unclear. This study examined the role of gut microbiota in host low-temperature stress resistance at molecular and biochemical levels in the oriental fruit fly Bactrocera dorsalis. The results showed that after the gut bacteria of flies were removed via antibiotic treatment, the median survival time was significantly decreased to approximately 68% of that in conventional flies following exposure to a temperature stress of 10˚C. Furthermore, we found that Klebsiella michiganensis BD177 is a key symbiotic bacterium, whose recolonization in antibiotic treated (ABX) flies significantly extended the median survival time to 160% of that in the ABX control, and restored their lifespan to the level of conventional flies. Notably, the relative levels of proline and arginine metabolites were significantly downregulated by 34and 10-fold, respectively, in ABX flies compared with those in the hemolymph of conventional flies after exposure to a temperature stress of 10˚C whereas recolonization of ABX flies by K. michiganensis BD177 significantly upregulated the levels of proline and arginine by 13-and 10-fold, respectively, compared with those found in the hemolymph of ABX flies. qPCR analysis also confirmed that K. michiganensis-recolonized flies significantly stimulated the expression of transcripts from the arginine and proline metabolism pathway compared with the ABX controls, and RNAi mediated silencing of two key genes Pro-C and ASS significantly reduced the survival time of conventional flies, postexposure low-temperature stress. We show that microinjection of L-arginine and L-proline into ABX flies significantly increased their survival time following exposure to temperature stress of 10˚C. Transmission electron microscopy (TEM) analysis further revealed that low-temperature stress caused severe destruction in cristae structures and thus resulted in abnormal circular shapes of mitochondria in ABX flies gut, while the recolonization of live K. michiganensis helped the ABX flies to maintain mitochondrial functionality to a normal status, which is important for the arginine and proline induction. Our results suggest that gut microbiota plays a vital role PLOS PATHOGENS PLOS Pathogens | https://doi.

Cold hardiness of the South American tomato pinworm Tuta absoluta (Lepidoptera: Gelechiidae): both larvae and adults are chill‐susceptible

“…58 Depressed SCPs are often attributed to absence of ice nucleating compounds as well as accumulation of cryoprotective elements in the gut. 10,32,60 Fasting eliminates gut contents likely resulting in reduction of the number of gut ice nucleating agents and depressed SCPs. 32,61 This is consistent with current larval results showing depressed SCPs with fasting.…”

“…4,5 Survival of these low temperatures is dependent on employing a suite of adaptive behavioural, morphological, molecular and physiological mechanisms, particularly in immobile diapausing (hibernating) and/or quiescent overwintering stages. [6][7][8][9][10] Indeed, the Bogert effect posits less mobile developmental stages have inherent higher physiological fitness owing to their limited behavioural compensatory capacities and evolutionary inertia to fitness traits. 11 Exact mechanisms facilitating survival in hibernating organisms may vary but includes; body water loss (e.g.…”

“…11 Exact mechanisms facilitating survival in hibernating organisms may vary but includes; body water loss (e.g. cryoprotective dehydration), 12 regulation of protein expression, 13 gut microbiota, 10 feeding cessation, expulsion of gut contents, depressed supercooling points (SCPs), accumulation of carbohydrate cryoprotectants and selection of favourable overwintering microhabitats (reviewed in the literature 3,14 ).…”

“…26,29 Recent studies also showed that gut microbiota also play a pivotal role in improving insect cold hardiness through stimulating their metabolism and signalling pathways. 10,30 For example, Klebsiella michiganensis BD177 has been reported to activate the arginine and proline metabolism pathway of invasive Bactrocera dorsalis resulting in tolerance to extreme low temperature stress through influencing the functionality of the mitochondria. 10 Given this background, it raises questions of how other invasive species overwinter and survive stressful low sub-zero winter temperatures.…”

Variability of Gut Microbiota Across the Life Cycle of Grapholita molesta (Lepidoptera: Tortricidae)

“…The larval midgut was homogenized and diluted to the appropriate concentration to spread on Luria Bertani (LB) agar plates (tryptone 10 g/L, yeast extract 5 g/L, NaCl 10 g/L, and agar 15 g/L). The plates were incubated at 37°C, and the differentiation of colonies in size, color, and morphology was observed every 24 h. Thereafter, a single representative isolate of each morphotype was transferred to new plates for three to four times purification, and each purified isolate (three to five colonies) was identified by PCR amplification of 16S rRNA gene using universal bacterial forward primer 27F (5′-AGAGTTTGATCCTGGCTCAG-3′) and reverse primer 1492R (5′-TACGGCTACCTTGTTACGACTT-3′; Thakur et al, 2015 ; Raza et al, 2020 ). PCR amplification was carried out with the following programs: 94°C for 3 min, 30 cycles at 94°C for 30 s, 55°C for 30 s, 72°C for 30 s, and a final extension at 72°C for 7 min.…”