Isolation and characterization of extremely halotolerant Bacillus species from Dead Sea black mud and determination of their antimicrobial and hydrolytic activities

Abstract

This is the first study that investigated the isolation of extremely halotolerant Bacillus species from Dead Sea black mud. Nine isolates obtained from black mud were considered to be extremely halotolerant Bacillus based on morphological, physiological, and biochemical properties. Most of their colonies were white to light yellow and circular to irregular. All isolates were Gram-positive rod-shaped endospore-forming bacteria, facultative anaerobes, oxidase negative, catalase positive, mesophilic, extremely halotolerant, reacted positively for tryptophan deaminase and Voges-Proskauer, hydrolyzed gelatin and aesculin, and assimilated potassium gluconate. Most of the isolates were found to hydrolyze o-nitrophenyl-beta-D-galactoside (ONPG) and p-nitrophenyl-β-D-galactopyranoside (PNPG) as well as arginine, and assimilate D-mannose, N-acetylglucosamine, D-maltose, and malic acid. All isolates were considered to be nitrate reducers, six of them were nitrite producers and three were N 2 producers, suggesting that they may play an important role in nitrification-denitrification processes and in the nitrogen cycle in soil. Based on 16S rRNA gene sequence analysis, the isolates were found to share very high identities (97-99%) with their closest phylogenetic relative and they were assigned to eight Bacillus species (B. oceanisediminis, B. subtilis, B. firmus, B. paralicheniformis, B. methylotrophicus, B. amyloliquefaciens, B. sonorensis, and B. malikii). Interestingly, several enzymatic activities were detected from nonhemolytic isolates DSM2 and DSM7 that were identified as B. paralicheniformis. It was found that only DSM2 isolate produced promising antimicrobial activities. Its aqueous extract showed the highest significant antifungal activity. Whereas, n-butanol and methanol extracts showed significant antibacterial and antifungal activities against human skin pathogens and against other frequent human pathogens.

Microbial communities in the Dead Sea and their potential biotechnological applications

“… Product Microorganism isolated from Dead Sea Hydrolytic enzymes Alpha-amylase Bacillus spp. [ 68 ]. Thermostable amylase, also stable at acidic conditions Bacillus strain HUTBS62 [ 69 ] Thermostable amyloglucosidase Halobacterium sodomense [ 70 ] Elastase Bacillus licheniformis 6t2 and 7t1 [ 68 ] Lipase Bacillus spp., Dead Sea mud [ 68 ].…”

“…[ 68 ]. Thermostable amylase, also stable at acidic conditions Bacillus strain HUTBS62 [ 69 ] Thermostable amyloglucosidase Halobacterium sodomense [ 70 ] Elastase Bacillus licheniformis 6t2 and 7t1 [ 68 ] Lipase Bacillus spp., Dead Sea mud [ 68 ]. Cellulase Halomicroarcula pellucida strain GUMF5 [ 71 ] Malate dehydrogenase Halobacterium sp [ 72 ].…”

“…[ 78 ]. Betaine Halobacillus dabanensis [ 79 ] Ectoine Halobacillus dabanensis [ 79 ] Exopolysaccharides Bioemulsifiers Haloferax mediterranei [ 80 ] Antimicrobials Antibacterial activity against Corynebacterium diphtheria 51696 Bacillus persicusi 24 DMS [ 2 ] Antibacterial activity was shown by halocin against S. aureus and P. aeruginosa Four isolates, type of microorganism was not characterized [ 43 ] Antifungal activity against C. albicans ATCC 10,231 and A. brasiliensis ATCC 16,404 Bacillus species DSM2 [ 68 ] β-carotene for food and cosmotic industries β-carotene D. salina [ 81 ] Cosmotic industry Astaxanthin D. salina [ 82 ] …”

“…Bacillus spp . isolates obtained from Dead Sea mud possessed amylase activity [ 68 ]. Thermo-stable amylase activity was reported from Bacillus strain HUTBS62 isolated from hot springs near the Dead Sea.…”

Recent Antimicrobial Responses of Halophilic Microbes in Clinical Pathogens

“…Bacillus persicus 24-DSMisolated from Dead Sea mud provided activity against B. subtilis and E. coli [79]. Another discovery revealed that the Bacillus species DSM2 from the same location has activity against pathogenic fungi, including C. albicans ATCC 10231 and A. brasiliensis ATCC 16404 (Maher 2017) [80].…”