Diverse Unidentified Legionella spp. Found in Antarctic Lakes
～ The possibility of species detected in Antarctic research station may be introduced by humans. ～
Summary
Legionella spp. are widely distributed in soil and freshwater environments. Legionella spp. can cause severe pneumonia via aerosol transmission, which emphasizes the importance of monitoring and infection prevention measures. They have been detected from water facilities such as bathtub water of Syowa Station in Antarctica, but it was still not clear whether Legionella spp., that are thought to grow in warm temperature, inhabit natural Antarctic environments and how they were introduced into the station.
Dr. Sho Shimada
Sho Shimada of Tokyo Medical and Dental University joined the 60th Japanese Antarctic Research Expedition (2018-2019) and collected samples from water facilities (e.g., water reservoir) of Syowa station, and 20 lakes in Antarctic natural environment to conduct a comprehensive survey of the potential environmental pathogens including Legionella. After returning to Japan, he extracted DNA from each sample and analyzed the bacterial communities using culture-independent PCR and sequencing analysis in collaboration with a team of researchers from the National Institute of Polar Research, Toho University, and the National Institute of Advanced Industrial Science and Technology (AIST).
The presence of Legionella-derived 16S rRNA gene sequences, phylogenetic markers of the genus, was confirmed in the samples of the water facilities of the station and all lakes. Some of the 16S rRNA gene sequences were detected in the samples from both the station and the lakes, suggesting that some of the Legionella spp. were introduced into the station from the surrounding environment. Meanwhile, Legionella spp., whose 16S rRNA gene sequences were detected only in the samples from the station, were suggested to have been brought into Antarctica by expedition members.
This is the first environmental survey of Legionella spp. in natural Antarctic environments. The results suggested that this genus may include a variety of species that have adapted to low temperatures. The colonization of species introduced to Antarctica by human activities illustrates the risk of transporting pathogens to isolated environments such as Antarctica and space and suggests a need for continuous monitoring.
Figure 1: Sampling. Skarvsnes Bosatsu Ike lake, about 50 km from the Syowa Station
Contents of Research
The purpose of this study was to comprehensively survey Legionella spp. and other waterborne pathogens that colonize Syowa Station, and to identify their potential sources.
From December 2018 to January 2019, as part of the 60th Japanese Antarctic Research Expedition, samples were collected from water facilities such as water reservoirs in Syowa Station, and glacial lakes located in ice-free areas in the vicinity of the station. These samples were brought back to Japan and were further analyzed. DNA was extracted from each sample, PCR-amplified targeting regions used for bacterial classification. These PCR products were comprehensively sequenced to analyze bacterial communities. Also, PCR amplification targeting specific regions for Legionella spp. was conducted to obtain a detailed understanding of their presence and distribution.
Analysis of the lake samples revealed that genera including pathogenic species such as Legionella spp., Pseudomonas spp., and Mycobacterium spp., are widely distributed in natural lakes. Legionella spp. was confirmed in all surveyed lakes. Furthermore, detailed analysis of the community structure of Legionella spp. confirmed that unexpectedly diverse Legionella spp. are distributed even in cold Antarctic lakes. Most of the Legionella-derived 16S rRNA gene sequences detected in this study had low sequence similarity with the previously described Legionella species, suggesting the wide distribution of yet-described species in Antarctica.
Bathtub in the administration building at Syowa Station.
Comparison of the Legionella spp. community detected at the station with that found in natural lakes revealed some sequences common to both communities, but a large proportion of the sequences from the community detected at the station were closely related to those of known pathogenic species. The rarity of detection of these species in Antarctic lakes suggests that they may have been introduced through human activities. Legionella spp. were not detected in water samples from the taps at the Syowa station (after water purification treatment).
