| dc.description.abstract | The silkworm, Bombyx mori L. is a commercially important insect species that exhibit
great temperature sensitivity and exhibit severe physiological and biochemical effects
in the larval stage. Global warming is one of the serious threats that adversely affects
the development and reproduction of silkworms. The optimum temperature for the
normal growth and metabolism of silkworm is 20°C to 30°C and above that affects
their regular development. Elevated temperatures have the potential to damage gut
tissues and may invite oxidative destruction, resulting in a decrease in both the
abundance of gut bacteria and the production of digestive enzymes. These enzymes
play a crucial role in nutrient absorption, influencing the overall development of
silkworms and the production of cocoons.
The growth, development, and
environmental adaptation of the host insect are greatly influenced by the gut
symbionts. Numerous bacteria that support metabolic activities are found in their gut;
however, very few studies have been reported about the diversity of these bacteria and
their role in the growth and development of the silkworm. The present study compares
the diversity of gut bacterial communities of silkworm under thermal stress and on
supplementation of vitamin C. In order to assess the impact of vitamin C under high
temperature 16S rRNA gene amplicon metagenomic analysis was conducted in the
gut of fifth instar larvae. The morphometric parameters of silkworm larvae, alterations
in the gut tissue, activity of digestive enzymes, mRNA expression levels of heat shock
proteins and economic performance of cocoons were also studied for analysing the
role of endosymbiotic bacteria in the development of the larvae and cocoon
formation.
Fifth instar larvae were divided into four groups in order to compare the diversity of
bacteria in their guts. One group was kept as control and fed with fresh mulberry
leaves alone; the second group was fed with fresh mulberry leaves and subjected to a
heat stress (40±2⁰C) for an hour per day throughout the experimental period; the third
group was fed with fresh mulberry leaves soaked in a 0.2% vitamin C solution; and
the fourth group was exposed to both temperature and 0.2% vitamin C
supplementation. The healthy fifth instar larvae were randomly sampled from each
group and guts were dissected out in sterile condition before being homogenised and
centrifuged for metagenomic analysis. The study used high throughput sequencing toevaluate the impact of gut microbes of silkworms in response to high temperature and
vitamin C supplementation.
The findings demonstrated that elevated temperature has a negative impact on the
intestinal microbes of silkworm compared to the control and vitamin C supplemented
group which were reared under optimum temperature (25 ± 3° C). Firmicutes,
Proteobacteria and Bacteroidetes were the common bacteria found in all the four
groups. The digestive process of silkworms may also be impaired by heat shock due
to their effect on digestive enzymes. In comparison to thermal stress group the
ascorbic acid-supplemented group were shown to have a higher level of enzyme
activity. The activity of digestive enzymes showed a significant reduction in the
thermal stress exposed group compared to the other experimental groups. Moreover, it
was observed that the group treated with heat shock and supplemented with ascorbic
acid showed a significantly increased activity than the group exposed to thermal
stress. The length and weight of silkworm larvae and cocoons also showed a
significant decrease when exposed to higher temperature but showed an elevation in
the vitamin C supplemented group. The impact of high temperature also altered the
gut architecture, and these changes may be detrimental to the normal functioning of
the gut. However, the use of vitamin C is proposed as a potential solution to
counteract the damages caused by the high temperatures. Vitamin C is known for its
antioxidant properties, and it is suggested to have the capability to mitigate the
negative effects of environmental stressors, such as high temperatures, on the gut
architecture.
So, the results indicated that heat shock has an impact on the intestinal microflora of
silkworms that control the activity of associated digestive enzymes which affects the
digestion and nutritional intake, eventually impacting the growth and development of
silkworm larvae and cocoons produced. These observations showed that the
supplementation of vitamin C has the potential to counteract the stress brought on by
heat shock even when subjected to high temperature. Moreover, vitamin C has the
ability for enhancing the economic characteristics of silk as well as for the growth and
development of silkworms by altering the gut bacterial diversity | en_US |
