Molecular microbial diversity of a spacecraft assembly facility

In ongoing investigations to map and archive the microbial footprints in va rious components of the spacecraft and its accessories, we have examined th e microbial populations of the Jet Propulsion Laboratory's Spacecraft Assem bly Facility (JPL-SAF). Witness plates made up of spacecraft materials, som e painted with spacecraft qualified paints, were exposed for similar to7 to 9 months at JPL-SAF and examined the particulate materials collected for t he incidence of total cultivable aerobic heterotrophs and heat-tolerant (80 degreesC for 15-min.) spore-formers. The results showed that the witness p lates coated with spacecraft qualified paints attracted more dust particles than the non-coated stainless steel witness plates. Among the four paints tested, witness plates coated with NS43G accumulated the highest number of particles, and hence attracted more cultivable microbes. The conventional m icrobiological examination revealed that the JPL-SAF harbors mainly Gram-po sitive microbes and mostly spore-forming Bacillus species. Most of the isol ated microbes were heat resistant to 80 degreesC and proliferate at 60 degr eesC. The phylogenetic relationships among 23 cultivable heat-tolerant micr obes were examined using a battery of morphological, physiological, molecul ar and chemotaxonomic characterizations. By 16S rDNA sequence analysis, the isolates fell into seven clades: Bacillus licheniformis, B. pumilus, B. ce reus, B. circulans, Staphylococcus capitis, Planococcus sp. and Micrococcus lylae. In contrast to the cultivable approach, direct DNA isolation, cloni ng and 16S rDNA sequencing analysis revealed equal representation of both G ram-positive and Gram-negative microorganisms.