Presence and enrichability of propanotrophs in subsoils
The potential for enriching the population of propane-oxidizing microorganisms was tested in two sets of subsoils which yielded a total of seven different subsoils. In a preliminary experiment propane was rapidly consumed after an 18-day lag phase in two subsoils, contaminated either by chlorinated solvents or by petroleum-derived hydrocarbons, and in one surface soil with no history of contamination. In a subsequent study with five variously contaminated subsoils, one subsoil could not be enriched for propane or methane consumption, but oxidations of these gases in the remainder of the subsoils were partially enriched. Linear regression was utilized to test for the possible enrichment of propane oxidation in these four subsoils. The regressions were adjusted to avoid any unjustified claim of greater success of the enrichment process than probably occurred in some of the treatments. Overall, three soils seemed to offer some evidence of enrichment over 5 weeks. A high degree of statistical significance $(P < 0.001)$ offered the best evidence that enrichment of propane-oxidizing activity occurred in one subsoil. Screening for propane-oxidizing bacteria in the subsoils resulted in the isolation of 51 bacterial species including several aerobic bacteria such as Variovorax paradoxus, Pseudomonas putida, and Rhodococcus rhodochrous. These species were all capable of growth on propane, 2-propanol, and n-propanol as sole sources of carbon and energy. Fatty Acid Methyl Ester (FAME) analysis of isolate JGiao22 showed no match with fatty acid profiles of different genera recorded in the Microbial Identification System (Microbial ID, Inc., Newark, DE). This isolate was further characterized utilizing partial 16S rRNA sequencing that indicated a close relation to the genus Variovorax. Isolate JGiao22 is a Gram negative, motile rod with peritrichous flagella, and contains two plasmids, a single gas vesicle, unique circular dense inclusions, and extracellular polymers. Our results justify naming this isolate as a new species, Variovorax propanotrophica sp. nov. JGiao22.
0768: Environmental science