Cardinium

Cardinium is a genus of intracellular bacteria belonging to the Cytophaga-Flavobacterium-Bacteroides (CFB) group, specifically within the Flavobacteriaceae family. These bacteria are notable for their parasitic or mutualistic relationship with a wide range of arthropods, including insects, mites, and spiders.

Characteristics and Biology

Cardinium bacteria are Gram-negative and primarily transmitted vertically from mother to offspring through the egg cytoplasm. Some horizontal transmission events are also suspected, although less understood. Their intracellular lifestyle requires them to reside within the cells of their arthropod hosts. They are obligate intracellular bacteria, meaning they cannot be cultured outside of a host cell.

Effects on Hosts

Cardinium infections are best known for manipulating the reproductive systems of their hosts. These manipulations, often referred to as cytoplasmic incompatibility (CI), promote the spread of Cardinium within host populations. CI typically manifests as embryonic lethality when an uninfected female mates with an infected male. Other reproductive manipulations caused by Cardinium can include parthenogenesis (asexual reproduction of unfertilized eggs), feminization (conversion of genetic males into females), and male killing (selective death of male offspring). These manipulations ultimately benefit the bacteria by increasing the proportion of infected females, which pass the infection to their offspring.

Classification and Phylogeny

Cardinium is a relatively recently defined genus, and its classification is constantly being refined as more genetic data becomes available. Phylogenetic analysis based on 16S rRNA gene sequences and other genetic markers reveals distinct Cardinium strains and lineages. These lineages often exhibit host specificity, meaning that certain Cardinium strains are associated with specific arthropod species or groups.

Research and Significance

Cardinium is a subject of ongoing research due to its significant impacts on arthropod biology and evolution. Understanding the mechanisms of its reproductive manipulations has implications for pest control strategies and evolutionary biology. Studies of Cardinium contribute to our knowledge of host-parasite interactions, bacterial evolution, and the genetic basis of reproductive strategies.