Microenvironment and bacterial community structure in the gut of wood- and litter-feeding cockroaches
While the gut microbiota of termites and its role in symbiotic digestion have been studied for decades, little is known about the bacteria colonizing the intestinal tract of detritivorous cockroaches. To improve the phylogenetic classification of short-read libraries, we first created a curated...
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|While the gut microbiota of termites and its role in symbiotic digestion have been studied for
decades, little is known about the bacteria colonizing the intestinal tract of detritivorous
To improve the phylogenetic classification of short-read libraries, we first created a curated
reference database of the bacterial 16S rRNA gene, based on the SILVA database and 1048
additional full-length 16S rRNA gene sequences from the intestinal tracts of 24 dictyopteran
insects (chapter 2). The performance of the database in the classification of short-read libraries from termites and cockroaches was highly superior to that of the current SILVA and RDP databases.
We then investigated the bacterial gut communities in the crop, midgut and hindgut of two
xylophagous (chapter 3) and three litter-feeding (chapter 4) cockroaches by Illumina
sequencing, and compared them to those in omnivorous cockroaches and termites, focusing on two main questions: First, if host diet determines the gut microbiota in cockroaches, and
second, what role environmental variables play in different gut compartments. We found that
the gut microbiotas of cockroaches share rare lineages and the phenomenon of gut
compartment-specific communities with those of termites, but differ in community structure
and show only little diet-specific distinction. In order to identify other potential drivers of
microbial community structure in cockroach guts, we determined the intestinal
physicochemical parameters pH, redox potential, and oxygen and hydrogen partial pressure.
Surprisingly, the localization of intestinal hydrogen accumulation in the crop of two cockroach
species differed from that in the posterior midgut observed previously for omnivorous species.
Intestinal pH, in addition to other, yet unidentified factors, was a strong determinant of bacterial community structure, posing a strong selection pressure particularly in the hindgut
For a better understanding of the digestion of lignocellulose by cockroaches in nature, I fed
two cockroach species on oak leaf litter, and determined the degradation efficiency and
metabolization rates of lignocellulosic fractions and carbohydrate monomers through
controlled mass balances (chapter 5). I found that xylan rather than cellulose was degraded in
the gut, suggesting that litter-feeding cockroaches preferentially degrade the easily
solubilizable diet fractions like hemicelluloses.