Vol.:(0123456789) 1 3 Biomass Conversion and Biorefinery https://doi.org/10.1007/s13399-022-03691-8 ORIGINAL ARTICLE Coal-vitamin medium for improved scheme of isolating biosurfactant-producing actinomycetes of rare species from soil samples Adilah Ayoib 1,2  · Subash C. B. Gopinath 2,3,4  · Ahmad Ramli Mohd Yahya 5  · Latifah Zakaria 5 Received: 21 September 2022 / Revised: 6 December 2022 / Accepted: 18 December 2022 © The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature 2023 Abstract A simplifed scheme for the isolation of biosurfactant-producing actinomycetes from soils was developed using diferent combinations of pretreatments and selective media supplemented with antifungal agent, cycloheximide (0.1 g/l). Pretreat- ments using hot air-drying techniques as well as soil suspension in phosphate bufer solution (5 mM, pH 7.0) treated with peptone (6%) at 45 °C for 10 min proved to be efectual in decreasing the number of vegetative bacterial cells while preserving many actinomycetes spores. Out of 945 actinomycetes isolates collected from various types of soils, 126 isolates of distinct morphologies were screened for biosurfactant production and 28 isolates were proven positive with 18 from contaminated areas while 10 of the positive isolates were from relatively non-contaminated soils. The combination of coal-vitamin medium, supplemented with antifungal agent, cycloheximide (0.1 g/L), on soil samples treated with peptone (6%) and SDS (0.05%) in 5 mM phosphate bufer, pH 7.0, produced the highest number of actinomycetes isolates recovery. Initial screenings for biosurfactant production using combination of microplate assay, drop collapse method, emulsifcation activity, and tributyrin agar test were found adequate for copious isolates as these methods also assessed for both low- and high-molecular mass biosurfactant types and worked well for high throughput screening analyses. Keywords Lipase · Microplate assay · Drop collapse method · Emulsifcation activity · Tributyrin agar 1 Introduction There have been increased eforts in isolating biosufactant producing actinomycetes from soils in the recent decades by applying a broad range of diferent screening methods for biosurfactant production, as well as using combinations of pretreatments of soils, various isolation media, and hav- ing hydrocarbon-contaminated sites as major sampling loca- tions. However, there is currently no consensus in the isolation method particularly for biosurfactant-producing actinomycetes especially from soils. Biosurfactants, or microbial surfactants are amphiphilic surface-active compounds produced by bacte- ria, yeasts, and fungi that reduce surface and interfacial tension and function heavily in industrial applications such as foods and beverages, pharmaceuticals, agrochemicals, petrochemi- cals, as well as organic chemicals [1]. Biosurfactants have great environmental susceptibility, which make them more pre- ferred over petroleum-based synthetic surfactants [2]. Bacterial biosurfactants receive even more attention due to their antibac- terial activity, lower toxicity towards plants and animals, high biodegradability, low irritancy, and compatibility with human skin [3]. Extensive studies have been conducted in search for the synthesis of various types of biosurfactants by many bac- teria, most notable from Pseudomonas sp. and Bacillus sp. [4], and yet studies on biosurfactant-producing actinomycetes are scarce, especially in Malaysia. Actinomycetes, which can also be used interchangeably with the term Actinobacteria, are * Adilah Ayoib adilahayoib@unimap.edu.my 1 Faculty of Chemical Engineering & Technology, Universiti Malaysia Perlis (UniMAP), 02100 Padang Besar, Perlis, Malaysia 2 Institute of Nano Electronic Engineering, Universiti Malaysia Perlis (UniMAP), 01000 Kangar, Perlis, Malaysia 3 Micro System Technology, Centre of Excellence (CoE), Universiti Malaysia Perlis (UniMAP), Pauh Campus, 02600 Arau, Perlis, Malaysia 4 Faculty of Chemical Engineering & Technology, Universiti Malaysia Perlis (UniMAP), 02600 Arau, Perlis, Malaysia 5 School of Biological Sciences, Universiti Sains Malaysia, 11800 USM Pulau Pinang, Malaysia