Cultivation of anaerobic and facultatively anaerobic bacteria from spacecraft-associated clean rooms

Abstract

In the course of this biodiversity study, the cultivable microbial community of European spacecraft-associated clean rooms and the Herschel Space Observatory located therein were analyzed during routine assembly operations. Here, we focused on microorganisms capable of growing without oxygen. Anaerobes play a significant role in planetary protection considerations since extraterrestrial environments like Mars probably do not provide enough oxygen for fully aerobic microbial growth. A broad assortment of anaerobic media was used in our cultivation strategies, which focused on microorganisms with special metabolic skills. The majority of the isolated strains grew on anaerobic, complex, nutrient-rich media. Autotrophic microorganisms or microbes capable of fixing nitrogen were also cultivated. A broad range of facultatively anaerobic bacteria was detected during this study and also, for the first time, some strictly anaerobic bacteria (Clostridium and Propionibacterium) were isolated from spacecraft-associated clean rooms. The multiassay cultivation approach was the basis for the detection of several bacteria that had not been cultivated from these special environments before and also led to the discovery of two novel microbial species of Pseudomonas and Paenibacillus.

FIG. 1.

Phylogenetic tree. This maximum-parsimony tree is based on 16S rRNA gene sequences of cultivable bacterial strains isolated from the two different spacecraft assembly facilities. Besides the isolates (bold), the closest neighbors are shown. If two or more isolate names are given, this strain was isolated several times. However, the 16S rRNA gene sequence of only one representative was submitted to GenBank. The GenBank accession numbers are given in parentheses. The scale bar shows a 10% estimated difference in nucleotide sequence positions.

FIG. 2.

Origin of organisms. Schematic drawing showing the location from which the different microorganisms were isolated. FR1, first sampling in Friedrichshafen (April 2007); FR2, second sampling (November 2007); ES, ESTEC sampling (March 2008). The middle box (gray) summarizes the organisms that were detected at all three samplings.

FIG. 3.

Quantitative diagram of isolates and their relationship to oxygen. This diagram shows the abundances of microorganisms with different oxygen requirements after enrichment and cultivation on media with different oxygen content. Anaerobes were strict anaerobes, growing only on oxygen-free medium. Facultative anaerobes were isolated on anaerobic and aerobic media and were capable of growing under both conditions. Aerobic isolates were obtained only on aerobic media, and whether they also had the ability to grow under anaerobic conditions was not tested (data not shown.).