Corncob structures in dental plaque reveal microhabitat taxon specificity

Background The human mouth is a natural laboratory for studying how bacterial communities differ across habitats. Different bacteria colonize different surfaces in the mouth – teeth, tongue dorsum, and keratinized and non-keratinized epithelia – despite the short physical distance between these habitats and their connection through saliva. We sought to determine whether more tightly defined microhabitats might have more tightly defined sets of resident bacteria. A microhabitat may be characterized, for example, as the space adjacent to a particular species of bacterium. Corncob structures of dental plaque, consisting of coccoid bacteria bound to filaments of Corynebacterium cells, present an opportunity to analyze the community structure of one such well-defined microhabitat within a complex natural biofilm. Here we investigate by fluorescence in situ hybridization and spectral imaging the composition of the cocci decorating the filaments. Results The range of taxa observed in corncobs was limited to a small subset of the taxa present in dental plaque. Among four major groups of dental plaque streptococci, two were the major constituents of corncobs, including one that was the most abundant Streptococcus species in corncobs despite being relatively rare in dental plaque overall. Images showed both Streptococcus types in corncobs in all individual donors, suggesting that the taxa possess different ecological roles or that mechanisms exist for stabilizing the persistence of functionally redundant taxa in the population. Direct taxon-taxon interactions were observed not only between the Streptococcus cells and the central corncob filament but also between Streptococcus cells and the limited subset of other plaque bacteria detected in the corncobs, indicating microhabitat specialization involving these taxa as well. Conclusions The spatial organization we observed in corncobs suggests that each of the microbial participants is capable of interacting with multiple, albeit limited, potential partners, a feature that may encourage the long-term stability of the community. Additionally, our results suggest the general principle that a precisely defined microhabitat will be inhabited by a small and well-defined set of microbial taxa.

On the ecology and biology of two endogean millipedes (Diplopoda: Julida: Julidae) endemic to the Western Rhodope Mtn., Bulgaria

Mountain slopes covered with stone debris have been of special interest for zoologists since the pioneer work of Juberthie et al. (1980) who defined and described the Milieu Souterrain Superficiel, most popularly referred to in English as the Mesovoid Shallow Substratum (MSS). Today this particular habitat is classified as one of the several types of MSS, namely the colluvial MSS. In a number of recent publications, the MSS is considered as one of the Superficial Subterranean Habitats (SSHs) within a broader concept of the subterranean domain. According to a widely accepted idea, the SSHs are different in their nature but are all characterized by the absence of light which is regarded as the main factor responsible for the occurrence of troglomorphic fauna in these habitats, along with epigean species that are able to live in such conditions. The present study focuses on two julid millipedes — Typhloiulus orpheus Vagalinski, Stoev & Enghoff, 2015 and a yet undescribed genus and species of the tribe Typhloiulini — occurring in the transitional layer of fine rubble between the soil stratum and the MSS in limestone taluses in the Western Rhodope Mtn. It was revealed that the spatial distributions of the two species in the studied sites were remarkably confined and follow the same pattern, which is suggested to reflect narrow microhabitat specialization. This assumption is further supported by certain traits in the morphology and biology of the two diplopods. It can be concluded that both T. orpheus and the new genus and species are essentially stenotopic endogean elements with strict requirements for an aphotic, mesophilous, limestone environment. Given the specific ecological conditions, which differ from both the overlying soil layer and the underlying colluvial MSS, together with the existence of certain narrowly adapted species, it is worth considering the recognition of the intermediate “microvoid” breakstone layer as a separate shallow subterranean habitat.