Oxygen Affects Gut Bacterial Colonization and Metabolic Activities in a Gnotobiotic Cockroach Model

Abstract

The gut microbiota of termites and cockroaches represents complex metabolic networks of many diverse microbial populations. The distinct microenvironmental conditions within the gut and possible interactions among the microorganisms make it essential to investigate how far the metabolic properties of pure cultures reflect their activities in their natural environment. We established the cockroach Shelfordella lateralis as a gnotobiotic model and inoculated germfree nymphs with two bacterial strains isolated from the guts of conventional cockroaches. Fluorescence microscopy revealed that both strains specifically colonized the germfree hindgut. In diassociated cockroaches, the facultatively anaerobic strain EbSL (a new species of Enterobacteriaceae) always outnumbered the obligately anaerobic strain FuSL (a close relative of Fusobacterium varium), irrespective of the sequence of inoculation, which showed that precolonization by facultatively anaerobic bacteria does not necessarily favor colonization by obligate anaerobes. Comparison of the fermentation products of the cultures formed in vitro with those accumulated in situ indicated that the gut environment strongly affected the metabolic activities of both strains. The pure cultures formed the typical products of mixed-acid or butyrate fermentation, whereas the guts of gnotobiotic cockroaches accumulated mostly lactate and acetate. Similar shifts toward more-oxidized products were observed when the pure cultures were exposed to oxygen, which corroborated the strong effects of oxygen on the metabolic fluxes previously observed in termite guts. Oxygen microsensor profiles of the guts of germfree, gnotobiotic, and conventional cockroaches indicated that both gut tissue and microbiota contribute to oxygen consumption and suggest that the oxygen status influences the colonization success. M any insects, particularly those feeding on a fiber-rich diet, possess a dense and complex microbiota. The most prominent examples are termites, whose ability to thrive on an entirely lignocellulosic diet depends on the digestive and nutritional contributions of microbial symbionts housed in their intestinal tracts (1, 2). During recent years, the microbial community structure of many termites has been studied in detail, and the evolutionary patterns in the gut microbiota of termites and their closest phylogenetic relatives, the cockroaches, are slowly emerging (3). In particular, the application of high-throughput sequencing techniques provides sufficient resolution and sampling depth to distinguish the phylogenetic and environmental drivers of the community structure (4,5,6).The functional roles of individual community members and their interactions, however, are more difficult to elucidate, mostly due to their formidable resistance to cultivation. Metagenomic and metatranscriptomic approaches have provided the first insights into the functional potentials of the gut community (7,8,9), but owing to the lack of reference genomes for many deepbranching lineages of the gut microbiot...

Deterministic Assembly of Complex Bacterial Communities in Guts of Germ-Free Cockroaches

“…Shelfordella lateralis was obtained from a commercial breeder and maintained as previously described (5). Germ-free cockroaches were obtained using the protocol described by Tegtmeier et al (9). Briefly, mature oothecae were washed quickly in 0.1% sodium dodecylbenzenesulfonate and then sterilized in 2% peracetic acid solution for 5 min.…”

“…Also their elaborate social structure makes them intractable as gnotobiotic models because earlier instars must be nourished by nest mates. In comparison, their closest relatives, the noneusocial cockroaches, do not depend on colony members for nourishment and can be raised in isolation under axenic conditions (9). Moreover, the physicochemical conditions in cockroach guts (5,10) are similar to those of many termites (11,12), which would offer a surrogate environment at least for those core lineages of gut microbiota that are shared with termites (5,6,13).…”

“…We recently developed a gnotobiotic cockroach model based on Shelfordella lateralis (9), an omnivorous cockroach from the family Blattidae, the sister group of the termites (14). Using this model, we experimentally tested if the cockroach gut habitat could play an important role in determining gut community structure by inoculating germ-free individuals of S. lateralis with gut microbiotas from a set of donor organisms that include both close (termites) and distant (mice) relatives of cockroaches.…”

Effect of Dietary Fiber Sources on In-Vitro Fermentation and Microbiota in Monogastrics

“…Previously, butyric acid had a high response on organic acids when used as feed additives. Gut microbiota contains numerous and diverse microbial populations [33], and in the past, the identification of porcine microbiota has been made using culture-dependent techniques.…”

Establishment of a gnotobiotic silkworm model

“…In general, mammals are used to evaluate the effects of lactic acid bacteria for promoting health and preventing disease (4,5). The influence of lactic acid bacteria and intestinal bacteria on the host is often studied using gnotobiotic animals in which specific bacterial species are maintained as viable bacteria in the intestinal tract (6)(7)(8)(9)(10)(11). The use of gnotobiotic animals allows for investigation of the effects of specific bifidobacterium and lactic acid bacteria on individual animals without confounding by other intestinal microbiota (12).…”