Invasive brown widow spiders found to host novel bacteria linked to chlamydia

Invasive brown widow spiders on three continents were heavily infected with a single strain of Rhabdochlamydia, a bacterium related to major human and animal pathogens including chlamydia. However, a bite from these spiders will not infect humans with chlamydia.

Until now, Rhabdochlamydia has only been found in a few organisms: a tick, a woodlouse, a cockroach, and another spider. And even then, it was a rare occurrence in all of these organisms.

Dr. Monica Mowery and colleagues from Ben-Gurion University of the Negev compared microbial communities in populations of brown widow spiders collected in South Africa (likely the spider’s native range) and invasive populations in Israel and the United States. The overwhelmingly predominant bacterium, Rhabdochlamydia, was found in 86% of the spiders examined. It was also found in the eggs of the female spiders, indicating that mother spiders transmit the bacteria to their offspring.

“Our results suggest that this dominant, widespread chlamydia bacterium plays an important role in the invasive brown widow,” said Dr. Mowery, an assistant professor at the City University of New York and former postdoctoral researcher at BGU.

The research was recently published in Scientific reports.

Characterizing potentially important and widespread bacterial symbionts is a step toward understanding their relevance for ecological interactions and responses to rapid environmental change. The high prevalence of Rhabdochlamydia in all tested spider populations suggests that it may play an important functional role and contribute to the spider’s invasion success.

The brown widow spider, Latrodectus geometricus, is an urban invasive species that is displacing native spider species in warm climates worldwide. These spiders have neurotoxic venom and can be dangerous to young children and the elderly.

Microbial relatives can influence the invasive spread and success of a species in a new environment and can shift or be lost during the invasion process. The South African brown widow spiders generally had more diverse bacterial strains compared to newer arrivals in Israel, where brown widows were first found in Tel Aviv in 1980, and in the United States, where spiders spread from southern Florida in the 2000s. This higher microbial diversity supports the idea that the invasive brown widow spider originated in southern Africa.

Other researchers included Prof. Yael Lubin and Prof. Michal Segoli of Ben-Gurion University of the Negev, Prof. Jennifer White, Dr. Eric Chapman and Laura Rosenwald of the University of Kentucky, Thembile Khoza of the South African National Biodiversity Institute and Robin Lyle of the Agricultural Research Council, South Africa.