Arabian Journal for Science and Engineering https://doi.org/10.1007/s13369-018-3597-0 RESEARCH ARTICLE - BIOLOGICAL SCIENCES Antimicrobial Activity and GC-MS Analysis of Bioactive Constituents of Thermophilic Bacteria Isolated from Saudi Hot Springs S. A. Alrumman 1 · Y. S. Mostafa 1 · Shekha T. S. Al-Qahtani 1,2 · T. Sahlabji 3 · T. H. Taha 4 Received: 26 May 2018 / Accepted: 8 October 2018 © King Fahd University of Petroleum & Minerals 2018 Abstract The bioactivity of thermophilic bacteria isolated from hot springs in the southern region of Saudi Arabia was investigated. Of the 84 bacterial isolates, the antimicrobial activity of 50 of them had an antagonistic effect against one or more of the tested human pathogens: Candida albican, Staphylococcus aureus, Proteus mirabilis, Klebsiella pneumonia and Shigella flexneri. Furthermore, four isolates exhibited the highest antagonistic ability against all pathogens. The molecular identification of selected promising isolates and phylogenetic analysis confirmed the accurate identity of the isolates as Bacillus sonorensis, Bacillus thermocopriae, Brevibacillus borstelensis and Brevibacillus parabrevis. GC-MS analysis of the cell-free extracts detected 40 secondary metabolites; each strain has its own secondary metabolites in addition to other compounds that are of industrial and pharmaceutical importance. The major secondary metabolites produced were cyclohexyl acrylate, imiloxan, tabtoxinine-β -lactam, nicotinyl alcohol, mephenesin, etomidate, L-menthyl lactate, (3-aminopropyl) dibutylborane, filbertone, and 1-dotriacontanol. These findings suggest a need to raise awareness of the value hot springs in Saudi Arabia have as locations for isolating thermophilic bacteria that could possibly serve as reservoirs for new bioactive compounds of industrial and medical importance. Keywords Hot springs · Thermophilic bacteria · Antagonism · Bioactivity 1 Introduction Hot springs are consistently among the hottest places in the world, and these regions are the main habitats of thermophilic bacteria [1]. These springs have various chemical and phys- ical properties, which support the growth of thermophilic bacteria [2]. Currently, there is a gap in knowledge regard- ing the potential of hot springs as a resource in Saudi Arabia [3]. There are ten hot springs dispersed throughout Saudi Arabia; however, the microorganisms in these springs have B S. A. Alrumman salrumman@kku.edu.sa 1 Department of Biology, College of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia 2 Department of Biology, College of Science, University of Bisha, P.O. Box 551, Bisha 61922, Saudi Arabia 3 Department of Chemistry, College of Science, King Khalid University, P.O. Box 9004, Abha 61413, Saudi Arabia 4 Environmental Biotechnology Department, Genetic Engineering and Biotechnology Research Institute, City of Scientific Research & Technological Applications, P.O. Box: 21934, Alexandria, Egypt yet to be investigated and characterised [4]. This resource has not yet been extensively exploited; however, it could be used as a potential source for electricity generation, heat- ing purposes, tourism, therapeutic benefits and as a source of novel bioactive metabolites. In general, few reports have been published concerning the biological activities of Saudi Ara- bia’s hot springs [5]. Thermophiles are organisms that have evolved to grow in extreme environments, and grow best at temperatures between 45 and 80 ◦ C. Due to their harsh envi- ronment, thermophilic bacteria largely remain a reservoir for biodiversity, molecular phylogeny, and the production of secondary metabolites [6]. There is an ongoing demand for new chemotherapeutics to combat new illnesses and drug-resistant pathogens that are becoming a considerable threat to public health. As microbial pathogens are continu- ally evolving and developing resistance towards antibiotics, there have been increased demands for the discovery and development of new and effective antimicrobial compounds [7]. Recently, there has been major interest in microbes that can exist under extreme environmental conditions such as thermophiles, whose secondary metabolism has been poorly understood until now [8]. Antimicrobial metabolites are pro- 123