Genomic and phenotypic characterization of Burkholderia isolates from the potable water system of the International Space Station
Year: 2020
Type: article
Abstract: The opportunistic pathogens Burkholderia cepacia and Burkholderia contaminans , both genomovars of the Burkholderia cepacia complex (BCC), are frequently cultured from the potable water system (PWS) of the International Space Station (ISS). Here, we sequenced the genomes and conducted phenotypic assays to characterize these Burkholderia isolates. All recovered isolates of the two species fall within monophyletic clades based on phylogenomic trees of conserved single-copy core genes. Within species, the ISS PWS strains all demonstrate greater than 99% average nucleotide identity (ANI), suggesting that they are of a highly similar genomic lineage and both individually may have stemmed from the two founding clonal strains before diverging into two unique sub strain populations. No evidence for horizontal gene transfer between the populations was observed. Differences between the recovered isolates can be observed at the pangenomic level, particularly within putative plasmids identified within the B. cepacia group. Phenotypically, the ISS-derived B. cepacia isolates generally exhibit a trend of lower rates and shorter duration of macrophage intracellularization compared to the selected terrestrial reference strain (though not significantly), and significantly lower rates of cellular lysis in 7 of the 19 isolates. ISS-derived B. contaminans isolates displayed no difference in rates of macrophage intracellularization compared to the selected reference, though generally increased rates lysis, with 2 of the 5 significantly increased at 12-hours post inoculation. We additionally find that ISS-isolated B. contaminans display hemolytic activity at 37°C not demonstrated by the terrestrial control, and greater antifungal capacity in the more recently collected isolates. Thankfully, the ISS-derived isolates generally exhibit 1-4 times greater sensitivity to common antibiotics used in their clinical treatments. Thus, despite their infection potential, therapeutic treatment should still have efficacy. Author Summary The International Space Station (ISS) is a unique built environment due to its isolation and recycling of air and water. Both microbes and astronauts inhabit the ISS, and the potential pathogenicity of the former is of great concern for the safety of the latter. The potable water dispenser (PWD) of the potable water system (PWS) on board the ISS was assembled in a cleanroom facility and then primed on Earth using an extensive process to ensure no gas bubbles existed within the lines that could lock the apparatus upon installation in orbit. The primed system sat dormant for 6 months before installation on the ISS. Microbial surveillance was conducted on the system after installation and the bacterial load was 85 CFU/mL, which exceeded the 50 CFU/mL limits set for ISS potable water. Over a microbial surveillance spanning 4.5 years, numerous strains of the potential pathogen Burkholderia have been isolated from the PWD. Here we sequenced and analyzed the genomes of these strains while also characterizing their potential pathogenicity. The genome analysis indicates it is likely that there were only two strains that were introduced on Earth that have subsequently undergone minimal diverging evolution. These strains retain pathogenicity, but remain susceptible to antibiotics, providing a potential therapeutic intervention in the event of infection.
Source: PLoS ONE
Language: English
Subfield: Epidemiology
Field: Medicine
Domain: Health Sciences
Open Access status: gold
Estimated APC paid: $1,695
Awards: G2127269916, THE DISEASE-CAUSING ORGANISMS BURKHOLDERIA MULTIVORANS B. CEPACIA GENOMOVARS OF THE B. CEPACIA COMPLEX (BCC) AS WELL AS AN UNCLASSIFIED SPECIES OF BURKHOLDERIA AND ITS RELATIVES RALSTONIA PICKETTII AND R. INSIDIOSA ACCOUNT FOR 60% OF THE BACTERIAL ISOLATES OBTAINED FROM THE FILTRATED WATER SYSTEM ON BOARD THE INTERNATIONAL SPACE STATION (ISS). MEMBERS OF THESE GENERA CAN SURVIVE LONG PERIODS IN A PLANKTONIC STATE IN DISTILLED WATER OR AS BIOFILMS WITHIN AN INFECTED INDIVIDUAL. THEY ARE ALSO NATIVELY RESISTANT TO SEVERAL ANTIBIOTICS LEAVING TREATMENT OPTIONS COMPLEX. FOR BCC ORGANISMS THIS COMPLEXITY IS INCREASED BY THE PHENOMENON OF BACTERIAL PERSISTENCE WHERE A GENETICALLY IDENTICAL SUBPOPULATION OF THE BACTERIA SUSTAINS UNDER HIGH ANTIBIOTIC CHALLENGE BY A REDUCTION IN METABOLISM AND OTHER UNKNOWN MECHANISMS. A HEALTHY ASTRONAUT COULD EASILY CLEAR A BCC OR RALSTONIA SP. INFECTION; HOWEVER AFTER PROLONGED SPACEFLIGHT A POTENTIALLY IMMUNOCOMPROMISED ASTRONAUT WITH REPEATED EXPOSURE TO THESE ORGANISMS COULD BE AT RISK FOR DISEASE. IN OUR WORK WITH BURKHOLDERIA PSEUDOMALLEI -THE CAUSATIVE AGENT OF MELIOIDOSIS- WE HAVE OBSERVED BY MEANS OF TRANSPOSON SEQUENCING (TNSEQ) THAT A COMMON SET OF GENES HELP THE WILDTYPE BACTERIA PERSIST REGARDLESS OF THE MODE OF ACTION OF THE ANTIBIOTIC USED FOR CHALLENGE. WE HAVE FOUND A CYSTEINE SYNTHASE GENE WHOSE INHIBITION COULD ENHANCE EXISTING ANTIBIOTICS BY INTERFERING WITH THE BACTERIASPECIFIC SULFUR ASSIMILATION AND CYSTEINE SYNTHESIS PATHWAYS. IT IS LIKELY THAT METABOLIC REGULATION PLAYS A ROLE IN THE ABILITY FOR BCC AND RALSTONIA STRAINS TO PERSIST IN THE ISS POTABLE WATER IN A PLANKTONIC STATE. IT IS ALSO PROBABLE THAT THE SAME MECHANISMS WHICH INCREASE SURVIVORSHIP CAN IN TURN ENHANCE VIRULENCE AND LEND TO PERSISTENT BIOFILMS IN THE GASTROINTESTINAL OR RESPIRATORY TRACT OF THE INFECTED INDIVIDUAL. TO UNDERSTAND THE MECHANISMS THAT WOULD CONTRIBUTE TO ALTERED VIRULENCE IN ISS BCC AND RALSTONIA SPECIES THE GENOMES OF 67 ISOLATES FROM 22 MISSIONS WILL BE SEQUENCED AND COMPARED TO THEIR RESPECTIVE ATCC BCC OR RALSTONIA STRAIN. THE POTENTIAL FOR INCREASED VIRULENCE WILL BE DETERMINED BY THE PRESENCE OF GENES CLUSTERED AS PATHOGENICITY ISLANDS IN THE RESPECTIVE GENOME. TO ESTABLISH IF THE STRAINS ARE BECOMING MORE RESISTANT TO ANTIBIOTICS A MINIMUM INHIBITORY CONCENTRATION (MIC) WILL BE DETERMINED FOR EACH ISOLATE USING SIX ANTIBIOTICS CURRENTLY USED TO TREAT THE INFECTIONS AND THEN COMPARED TO THE RESPECTIVE ATCC CONTROL STRAIN. FINALLY A TRANSPOSON LIBRARY WILL BE GENERATED FOR THE MOST VIRULENT RESISTANT TOLERANT OR PERSISTENT STRAIN AND THIS LIBRARY WILL BE CULTURED IN DISTILLED WATER TO SIMULATE CONDITIONS ON THE ISS. HERE WE WILL IDENTIFY GENES WHICH AID IN THE SURVIVORSHIP OF BCC AND RALSTONIA STRAINS IN THE WATER SYSTEM OF THE ISS. THE KNOWLEDGE GAINED FROM THIS GENOMIC SEQUENCING AND TNSEQ STUDY WILL ALLOW US TO ASSESS ANY INCREASED VIRULENCE OR INFECTION POTENTIAL AS WELL AS HELP TO MAKE ANTIBIOTIC RECOMMENDATIONS PREDICT TARGET GENES WHERE INHIBITION BY ADJUVANTS WILL ENHANCE ANTIBIOTIC THERAPY OR PRESENT NOVEL WATER TREATMENT OPTIONS TO ERADICATE THE BCC/RALSTONIA STRAINS FROM THE POTABLE WATER OF THE ISS.
OpenAlex ID: W3008649742