‘Candidatus Xiphinematincola pachtaicus' gen. nov., sp. nov., an endosymbiotic bacterium associated with nematode species of the genus Xiphinema (Nematoda, Longidoridae)

Abstract

An intracellular bacterium, strain IAST, was observed to infect several species of the plant-parasitic nematode genus Xiphinema (Xiphinema astaregiense, Xiphinema incertum, Xiphinema madeirense, Xiphinema pachtaicum, Xiphinema parapachydermum and Xiphinema vallense). The bacterium could not be recovered on axenic medium. The 16S rRNA gene sequence of IAST was found to be new, being related to the family Burkholderiaceae, class Betaproteobacteria. Fungal endosymbionts Mycoavidus cysteinexigens B1-EBT (92.9 % sequence identity) and ‘Candidatus Glomeribacter gigasporarum’ BEG34 (89.8 % identity) are the closest taxa and form a separate phylogenetic clade inside Burkholderiaceae. Other genes (atpD, lepA and recA) also separated this species from its closest relatives using a multilocus sequence analysis approach. These genes were obtained using a partial genome of this bacterium. The localization of the bacterium (via light and fluorescence in situ hybridization microscopy) is in the X. pachtaicum females clustered around the developing oocytes, primarily found embedded inside the epithelial wall cells of the ovaries, from where they are dispersed in the intestine. Transmission electron microscopy (TEM) observations supported the presence of bacteria inside the nematode body, where they occupy ovaries and occur inside the intestinal epithelium. Ultrastructural analysis of the bacterium showed cells that appear as mostly irregular, slightly curved rods with rounded ends, 0.8–1.2 µm wide and 2.5–6.0 µm long, possessing a typical Gram-negative cell wall. The peptidoglycan layer is, however, evident only occasionally and not detectable by TEM in most cells. Another irregularly occurring shell surrounding the endosymbiont cells or the cell clusters was also revealed, probably originating from the host cell membrane. Flagella or spore-like cells do not occur and the nucleoid is diffusely distributed throughout the cell. This endosymbiont is transmitted vertically through nematode generations. These results support the proposal of IAST as a new species, although its obligate intracellular and obligate endosymbiont nature prevented isolation of a definitive type strain. Strain IAST is therefore proposed as representing ‘Candidatus Xiphinematincola pachtaicus’ gen. nov., sp. nov.

Discovery of Early-Branching Wolbachia Reveals Functional Enrichment on Horizontally Transferred Genes

“…Microbes could play significant roles in the biology of plant-parasitic nematodes (PPNs), which cause up to 25% of global crop yield loss and cost ∼$100 billion annually ( Nicol et al, 2011 ). Recent findings suggest PPNs can harbor mutualist symbionts, like Xiphinematobacter (Verrucomicrobia) ( Vandekerckhove et al, 2000 ; Brown et al, 2015 ) and Xiphinematincola (Burkholderiales) ( Palomares-Rius et al, 2016 , 2021 ), or symbionts with unknown phenotypes, including Cardinium (Bacteroidetes) ( Noel and Atibalentja, 2006 ; Brown et al, 2018 ) and Wolbachia (Alphaproteobacteria) ( Haegeman et al, 2009 ; Brown et al, 2016 ), but current studies on the diversity and roles of such microbes are limited.…”

Multi-omics Reveal the Enabling Factors of Aplastic Anaemia

“…We also noted a decrease in the abundance of Nematoda in eukaryotes identi ed in aplastic anaemia patients and a decrease in the abundances of Enoplea, Trichinellida, Trichuridae, Enterocytozoon and Trichuris within this phylum, which were negatively correlated with the contents of eicosenoate, docosatetraenoate and 10-transsheptadecenoate in the plasma. In addition, the number of Mycoavidus species 37 in the nematode-related bacterial community was decreased and negatively correlated with docosadienoate and docosatetraenoate. Previous studies have shown that nematodes are primarily associated with unsaturated fatty acids, consistent with our ndings.…”

Description of Rotylenchus zhongshanensis sp. nov. (Tylenchomorpha: Hoplolaimidae) and discovery of its endosymbiont Cardinium

“…The genus Cardinium has already recovered from root lesion nematode P. penetrans (Denver et al , 2016) and cyst nematodes belonging to genera Globodera and Heterodera (Shepherd et al , 1973; Endo, 1979; Walsh et al , 1983a, b; Yang et al , 2017). Other endosymbiont bacteria reported from nematodes belong to the genera Xiphinematincola pachtaicus , Wolbachia and Xiphinematobacter (Haegeman et al , 2009; Palomares-Rius et al , 2014, 2021). During the present study, the endosymbiosis of a Cardinium sp.…”