RESUMO
Two aerobic endospore-forming bacteria (AEFB), isolates SAB19 and SAD18, capable of biosurfactant production were isolated from a sediment core sampled from Mfabeni peatland, St Lucia, KwaZulu-Natal, South Africa. The isolates were screened for biosurfactant activity using drop collapse assay, hemolysis assay, oil spreading assay, emulsification, and surface tension measurement. The effect of environmental parameters--temperature [35 - 100 °C], pH [3.0 - 10.0], and salinity [0.5 - 15%]--on biosurfactant stability was also determined. Ultra-performance liquid chromatography in conjunction with electrospray ionization time-of-flight mass spectrometry (UPLC ESI-TOF MS) analysis revealed that both isolates produced surfactin isomers and a common mass peak of m/z 1326.1 that was ascribed to a precursor of the antibiotic plantazolicin (PZN). Isolate SAD18 was also found to produce the lipopeptides fengycin and iturin. Taxonomic classification based on partial 16S rRNA gene sequencing revealed that isolates SAB19 and SAD18 belonged to the Brevibacillus and Bacillus genera, respectively. The GenBank accession numbers obtained for SAB19 and SAD18 are MW429226 and MW441217. Biosurfactant extracts from isolate SAD18 exhibited the greatest level of surfactant activity and stability over the range of environmental parameters tested. Although no novel biosurfactants were identified, it was confirmed that the peatland environment represents an untapped source of microbial diversity with potential biotechnological applications.
