Isolation and cultivation of a novel Legionella species from an Antarctic Lake:
The first cold-tolerant representative in this genus
Legionella spp. are widely distributed in soil, freshwater and even in human-made water facilities such as cooling towers and circulating bathes. Since these bacteria can cause severe pneumonia via aerosols, it is important to monitor and control its proliferation in environments that could be sources of infection. The optimal growth temperature of Legionella spp. was generally thought to be around 36℃, but in recent years, Legionella-derived gene sequences have been detected even in low temperature environments. Moreover, a variety of unidentified Legionella-derived gene sequences had been detected in the water supply system at Syowa Station in Antarctica and in lakes around the station.
In this study, a research team including Sho Shimada, MD, PhD (Department of Microbiology and Infectious Diseases, Toho University Faculty of Medicine / Department of Respiratory Medicine, Tokyo Medical and Dental University), Ryosuke Nakai, PhD (Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology) and members from Toho University, National Institute of Polar Research and others successfully isolated a Legionella strain from lake sediments collected in Antarctica during the 60th Japanese Antarctic Research Expedition (2018-2019) (Fig. 1).
Fig. 1: Legionella antarctica isolated from Antarctic lake sediments. (Left) Grayish-white colonies formed on agar medium. (Right) Parasitic invasion of an amoeba (yellow arrows indicate Legionella cells).
A detailed examination revealed that the cultured strain is a novel species that can grow under low temperature conditions of 4-25℃.
Moreover, this strain showed the ability to accumulate unsaturated fatty acids inside the cell which may help maintain cell membrane fluidity even under low temperature conditions. Through comparative genomic analysis, we also found that this strain possessed many “mobile gene elements” that can transpose their position in the genome, affecting expression of other genes. These features are thought to be responsible for the adaptation to low temperatures.
The research team named this novel species Legionella Antarctica, after the Antarctic continent. This species is the first cold-tolerant representative of the genus Legionella.
Further studies of this strain are expected to provide insights into the detection and control of Legionella spp. in low-temperature environments.
The results of this research were published online on October 21 (Japan time) in Microbiology spectrum, a journal published by the American Society of Microbiology.
Fig. 2: Lake "Nagaike" (A) and its bottom (B), the source of isolation of Legionella from Antarctica. At the bottom of the lake, the presence of "moss monks" has been confirmed, in which mosses grow like towers. Photo by National Institute of Polar Research
Title of paper
Characterization of the first cultured psychrotolerant representative of Legionella from Antarctica reveals its unique genome structure