The scarab gut: A potential bioreactor for bio‐fuel production

Abstract

Cellulose and hemicelluloses are the most prevalent sources of carbon in nature. Currently many approaches employ micro‐organisms and their enzyme products to degrade plant feedstocks for production of bioenergy. Scarab larvae are one such model. They consume celluloses from a variety of sources including plant roots, soil organic matter and decaying wood, and are able to extract nutrients and energy from these sources. In this paper, we review the physicochemical properties of the scarab larval gut, the diversity and digestive role that microflora play in the scarab gut and discuss the potential for applying these digestive processes in bioreactors for improving bio‐fuel production. Scarab larvae are characterised by their highly alkaline midgut which is dominated by serine proteinase enzymes, and a modified hindgut which harbors the majority of the intestinal microbiota under anaerobic conditions. Evidence suggests that digestion of recalcitrant organic matter in scarab larvae likely results from a combination of endogenous gut proteinases and cellulolytic enzymes produced by symbiotic micro‐organisms. Most of the easily digestible proteins are mobilized and absorbed in the midgut by endogenous proteinases. The hindgut contents of scarab larvae are characterized by high concentrations of volatile fatty acids, the presence of fermenting bacteria, and typical anaerobic activities, such as methanogenesis. The hindgut typically contains a wide diversity of micro‐organisms, some of which appear to be obligate symbionts with cellulolytic potential. As a result, the scarab larval gut can be regarded as a small bioreactor resembling the rumen of sheep or cattle, where solid food particles composed of cellulose, hemicellulose, pectin and polysaccharides are degraded through enzymatic and fermentation processes. Together these observations suggest scarab larvae have potential to assist the bio‐fuel industry by providing new sources of (hemi)cellulolytic bacteria and bacterial (hemi)cellulolytic enzymes.

Multiorganismal Insects: Diversity and Function of Resident Microorganisms

“…Microbial function and growth may also be favored by the ions and metabolites delivered to the hindgut in the filtrate from the Malpighian tubules. In many insects, the ileum displays no evident morphological or physiological adaptations to maintain microorganisms, but the ileum of some insects (e.g., termites, scarab beetles) is expanded to form an anoxic fermentation chamber in which the microbiota degrade complex plant polysaccharides into products utilizable by aerobic metabolism of the insect (14, 54). In many insect taxa, the cuticle of the hindgut is thrown into spines and plates, and microorganisms can preferentially adhere to these structures (14).…”

The Microbiome of Spodoptera littoralis: Development, Control and Adaptation to the Insect Host

“…The hindgut is involved in water resorption [129]. The microbiota in the ileum of the hindgut of scarab beetles metabolizes plant polysaccharides into components that can be used by the insect [130]. In contrast to the hindgut, the midgut is an unfavorable environment for microorganisms.…”

Analysis of gut bacterial diversity and exploration of cellulose-degrading bacteria in xylophagous insects

“…초식성 곤충은 먹이로써 다양한 수종을 이용할 수 있지만 (Despres et al, 2007), 대부분의 식물은 독성을 지니고 있으며 소화하기 힘든 lignocellulose로 구성되어 있어서 대부분의 동물들이 이용하 기 어렵거나 불가능하다 (Watanabe and Tokuda, 2010). 초식 성 곤충의 장내에 공생하는 미생물들은 바이오매스를 분해하 는 역할을 수행하며 (Shi et al, 2011), 이곳에서 발견한 새로운 미생물이 생산하는 효소를 바이오연료 분야에 적용할 수 있을 것이다 (Cook and Doran-Peterson, 2010;Huang et al, 2010).…”