“CandidatusHepatoplasma crinochetorum,” a New, Stalk-Forming Lineage ofMollicutesColonizing the Midgut Glands of a Terrestrial Isopod

Abstract

Uncultivated bacteria that densely colonize the midgut glands (hepatopancreas) of the terrestrial isopodPorcellio scaber (Crustacea: Isopoda) were identified by cloning and sequencing of their 16S rRNA genes. Phylogenetic analysis revealed that these symbionts represent a novel lineage of the Mollicutes and are only distantly related (<82% sequence identity) to members of the Mycoplasmatales and Entomoplasmatales. Fluorescence in situ hybridization with a specific oligonucleotide probe confirmed that the amplified 16S rRNA gene sequences indeed originated from a homogeneous population of symbionts intimately associated with the epithelial surface of the hepatopancreas. The same probe also detected morphotypically identical symbionts in other crinochete isopods. Scanning and transmission electron microscopy revealed uniform spherical bacterial cells without a cell wall, sometimes interacting with the microvilli of the brush border by means of stalk-like cytoplasmic appendages, which also appeared to be involved in cell division through budding. Based on the isolated phylogenetic position and unique cytological properties, the provisional name "Candidatus Hepatoplasma crinochetorum" is proposed for this new taxon of Mollicutes colonizing the hepatopancreas of P. scaber.The common woodlouse, Porcellio scaber (Crustacea: Isopoda), is a cosmopolitan species that feeds mainly on decaying plant material, such as leaf litter, wood, and grass (29), which are rich in recalcitrant structural polymers, such as cellulose, hemicelluloses, and lignins (3). Together with other terrestrial isopods (Oniscidea), P. scaber is thought to play an important role in decomposition processes and nutrient recycling (29).The hepatopancreas (digestive glands) of P. scaber, which consists of two pairs of tubular midgut ceca, functions in the secretion of digestive enzymes and the absorption of nutrients. The midgut ceca are densely colonized by microorganisms (8,25,27,28,31). It has been speculated that hepatopancreatic bacteria, like the gut symbionts of termites and other soil arthropods that feed on fiber-rich diets (3, 4), might be involved in the digestion of leaf litter, e.g., by producing cellulases or phenol oxidases (28,(30)(31)(32).Like many previous attempts to isolate bacteria associated with invertebrates, all efforts to culture the symbionts in vitro have failed. This has so far prevented both identification of the symbionts and analysis of the nature of the symbiotic association. In a previous report, it was shown that the hepatopancreas of P. scaber is colonized by a novel lineage of rod-shaped, stalk-forming symbionts that fall into the alpha subclass of the Proteobacteria but are only distantly related to the Rickettsiales (Ͻ81% sequence similarity) (25). In the course of a broader survey of the distribution of such Rickettsia-like symbionts among different populations of P. scaber, we observed that in many specimens the hepatopancreas contained spherical symbiotic bacteria instead of the rod-shaped forms.In the present stu...

Biofilm feeding: Microbial colonization of food promotes the growth of a detritivorous arthropod

“…Hepatopancreatic glands were not sampled as the bacterial community of Porcellio scaber is represented by resident symbiotic bacteria which are acquired from the environment during early life (Wang et al 2007). Only two microbial species have been identified in the lumen of the hepatopancreas in Porcellio scaber : Candidatus Hepatoplasma and Candidatus Hepatincola, which according to phylogenetic analyses cluster with Mycoplasmatales (Mollicutes) and Rickettsiales (α-Proteobacteria), respectively (Wang et al 2004a; Wang et al 2004b). Total DNA was extracted from the guts of 36 individuals (n = 6 per experimental group), and biofilm was scraped from the food samples (n = 2 per group) using the Wizard genomic DNA Purification kit (Promega).…”

Growth rate and survival of terrestrial isopods is related to possibility to acquire symbionts

“…[22,35]). The microbial community of hepatopancreas is considered to be very specific, only two microbial species have been identified in lumen of hepatopancreas; Candidatus Hepatoplasma and Candidatus Hepatincola [32,33]. These two bacterial species never occur together and the infection is most likely possible only through feeding on dead conspecifics; these bacteria could not be detected in faeces, soil or leaf litter [15].…”

“CandidatusBacilloplasma,” a Novel Lineage ofMollicutesAssociated with the Hindgut Wall of the Terrestrial IsopodPorcellio scaber(Crustacea: Isopoda)

“…These bacteria are morphologically distinct and differ from other bacteria observed in the P. scaber digestive system (references 15,25,39, and 40; summarized in ref- erence 26).…”