Abstract
Gut microbiota has diverse ecological and evolutionary effects on its hosts. However, the ways in which it responds to environmental heterogeneity and host physiology remain poorly understood. To this end, we surveyed intestinal microbiota of Holotrichia parallela larvae at different instars and from different geographic regions. Bacterial 16S rRNA gene clone libraries were constructed and clones were subsequently screened by DGGE and sequenced. Firmicutes and Proteobacteria were the major phyla, and bacteria belonging to Ruminococcaceae, Lachnospiraceae, Enterobacteriaceae, Desulfovibrionaceae and Rhodocyclaceae families were commonly found in all natural populations. However, bacterial diversity (Chao1 and Shannon indices) and community structure varied across host populations, and the observed variation can be explained by soil pH, organic carbon and total nitrogen, and the climate factors (e.g., mean annual temperature) of the locations where the populations were sampled. Furthermore, increases in the species richness and diversity of gut microbiota were observed during larval growth. Bacteroidetes comprised the dominant group in the first instar; however, Firmicutes composed the majority of the hindgut microbiota during the second and third instars. Our results suggest that the gut's bacterial community changes in response to environmental heterogeneity and host's physiology, possibly to meet the host's ecological needs or physiological demands.
Highlights
It is well known that a wide diversity of insects harbor a number of commensal and mutualistic micro-organisms that have important ecological and evolutionary effects on their hosts [1,2,3,4]
By surveying the bacterial composition and variation of these communities, we examined the following subjects: (i) the composition and diversity of gut bacterial communities of H. parallela larvae; (ii) whether the community composition differs between natural population or larval stages; and (iii) if variation exists, whether and how environmental factors or life stages account for this variation
Using the Denaturing Gradient Gel Electrophoresis (DGGE) technique and the analysis of the 16S rDNA clone libraries, we have identified bacteria that are associated with the H. parallela larval host over a broad geographic distribution
Summary
It is well known that a wide diversity of insects harbor a number of commensal and mutualistic micro-organisms that have important ecological and evolutionary effects on their hosts [1,2,3,4]. Previous studies have shown that these microbial communities can provide their hosts with many rewards, including a supply of nutrients [1,4,5,6,7,8], contributions to host reproduction and survival [9,10], protection against natural predators and parasites [11,12], detoxification [13,14], and enhanced social interactions [15]. The abundance and distribution of these microbial communities have been recently explored in diverse insects, how environmental factors and host physiology affect the composition and diversity of the intestinal microbiota in the host is mostly unknown [10,16,17]. Climate change [20], soil attributes [21], and plant species [22] are important in determining the structure and composition of soil bacterial communities. Whether and how the environmental conditions influence the structure of the bacterial communities in the guts of soil-dwelling insects remains poorly understood
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