Overlapping Community Compositions of Gut and Fecal Microbiomes in Lab-Reared and Field-Collected German Cockroaches

Abstract

German cockroaches, Blattella germanica (Blattodea: Ectobiidae), are human commensals that move freely between food and waste, disseminating bacteria, including potential pathogens, through their feces. However, the relationship between the microbial communities of the cockroach gut and feces is poorly understood. We analyzed the V4 region of the 16S rRNA gene and the V9 region of the 18S rRNA gene by next-generation sequencing (NGS) to compare the bacterial and protist diversities in guts versus feces and males versus females, as well as assess variation across cockroach populations. Cockroaches harbored a diverse array of bacteria, and 80 to 90% of the operational taxonomic units (OTUs) were shared between the feces and gut. Lab-reared and field-collected cockroaches had distinct microbiota, and whereas lab-reared cockroaches had relatively conserved communities, considerable variation was observed in the microbial community composition of cockroaches collected in different apartments. Nonetheless, cockroaches from all locations shared some core bacterial taxa. The eukaryotic community in the feces of field-collected cockroaches was found to be more diverse than that in lab-reared cockroaches. These results demonstrate that cockroaches disseminate their gut microbiome in their feces, and they underscore the important contribution of the cockroach fecal microbiome to the microbial diversity of cockroach-infested homes.IMPORTANCE The German cockroach infests diverse human-built structures, including homes and hospitals. It produces potent allergens that trigger asthma and disseminates opportunistic pathogens in its feces. A comprehensive understanding of gut and fecal microbial communities of cockroaches is essential not only to understand their contribution to the biology of the cockroach, but also for exploring their clinical relevance. In this study, we compare the diversity of bacteria and eukaryotes in the cockroach gut and feces and assess the variation in the gut microbiota across cockroach populations.

Keywords: Blattella microbiota; German cockroach; fecal microbiota; feces; gut; indoor microbiome; microbiome.

FIG 1

Relative abundance of bacterial phyla, including Blattabacterium spp., in whole-insect samples. (a) Lab-reared and field-collected German cockroaches. Each bar depicts the mean relative abundance value of independent replicates (lab = 8, field = 20). (b) Male and female lab-reared and field-collected B. germanica cockroaches presented by location (Apt, apartment). Bars depict the mean relative abundance values of independent replicates (for Lab, male [M] = 4, female [F] = 4; for Apt1, M = 3, F = 3; for Apt2, F = 3; for Apt3, M = 2, F = 3; for Apt4, M = 3, F = 3).

FIG 2

(a) The distribution of bacterial taxa at the family level in whole-body samples of male and female B. germanica cockroaches from lab-reared and field-collected cockroaches. Data include Blattabacterium species. Box plots show the alpha diversities of (b) Shannon diversity indices and (c) Phylogenetic diversity among the whole-insect samples by location. (b and c) Bars delineate the median, and “x” defines the mean, the hinges represent the lower and upper quartiles, the whiskers extend to the most extreme values (no more than 1.5 times the interquartile range from the box), and outliers are plotted as circles, if present. Sample sizes for whole-insects are Lab = 8, Apt1 = 6, Apt2 = 3, Apt3 = 5, Apt4 = 6. UC, unclassified. In panels b and c, different lowercase letters over the bars indicate statistically significant differences between treatments (Kruskal-Wallis test, P < 0.05)

FIG 3

Principal-coordinate analysis depicting differences in taxonomic compositions of bacterial communities among independent replicates of lab-reared and field-collected whole German cockroach samples (males, triangles; females, circles). Community composition dissimilarity is based on the unweighted UniFrac (a) and Bray-Curtis dissimilarity (b) metrics. The percent variation explained by each component is indicated on the axis.

FIG 4

Blattabacterium reads in various tissue samples obtained from lab-reared and field-collected male and female German cockroaches. Error bars represent the standard error of the mean (SEM).

FIG 5

(a) Bar chart depicting the distribution of bacterial taxa at the family level in whole-gut and fecal matter samples of male and female B. germanica cockroaches from lab-reared and field-collected samples presented by location. Blattabacterium was excluded from this analysis. Each bar depicts the mean relative abundance value of independent replicates (Lab male, gut [G] = 4, fecal matter [FM] = 4; Lab female, G = 5, FM = 5; Apt1 male, G = 4, FM = 3; Apt1 female, G = 4, FM = 4; Apt2 male, G = 4, FM = 4; Apt2 female, G = 4, FM = 4; Apt3 male, G = 4, FM = 4; Apt1 female, G = 4, FM = 4). (b and c) Venn diagrams representing the shared OTUs between gut and feces in lab-reared (b) and field-collected (c) B. germanica adults.

FIG 6

Principal-coordinate analysis depicting differences in taxonomic compositions of bacterial communities among independent replicates of lab-reared and field-collected whole German cockroaches in gut and fecal samples after removing Blattabacterium reads. Community composition dissimilarity is based on the Bray-Curtis dissimilarity metric. The percent variation explained by each component is indicated on the axis.

FIG 7

Venn diagrams representing the number of shared OTUs between lab-reared and field-collected B. germanica adults. Sample sizes for lab were male = 4, female = 4; for the field, male = 8, female = 12.

FIG 8

The eukaryotic component of the cockroach microbiome among female and male whole-insect, whole-gut, and fecal samples of B. germanica by location. WI, whole insect; F, feces; G, gut. (a) Alpha-diversity boxplots using the Shannon index. For each group, the bars delineate the median, the hinges represent the lower and upper quartiles, the whiskers extend to the most extreme values (no more than 1.5 times the interquartile range from the box), and outliers are plotted in circles, if present. (b) Nonmetric multidimensional scaling (NMDS) using the Bray-Curtis dissimilarity. (c) Relative abundances of eukaryotic taxa.