Microorganisms in Pristine Cave Environments: Comparison
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Please note this is a comparison between Version 2 by Catherine Yang and Version 1 by Patrícia Gatinho.

Microorganisms are essential to life on Earth and can be found almost everywhere. In pristine environments, through evolutionary change, microorganisms have developed strategies adapted to such hostile conditions. They have adapted their metabolism to survive in extreme conditions with low levels of elements, such as carbon, nitrogen, and phosphorus, as well as the chemical composition of the surfaces, which directly affect community diversity. This occurs specifically in caves, which are natural geological formations formed by cavities in the rock and are considered extreme and unfavorable living environments due to severe abiotic conditions. Colonization of substrates in caves is not homogeneous. Different groups of microorganisms occupy different ecological niches in different caves, and together with cave fauna and environmental factors, such as carbon dioxide, temperature, and organic matter content, they determine the biotic functions of caves. Microorganisms colonize in host rock and detrital sediments with different compositions and/or structures, where minerals act as environmental filters that provide specific microhabitats for metabolically similar microorganisms. Microbial colonization is ultimately a complex and dynamic process determined and controlled by physicochemical characteristics and biochemical factors. 

  • anticancer activity
  • antimicrobial activity
  • bioactive compounds
  • microorganisms

1. Identification of Microorganisms

Identification of microorganisms can be performed using classical microbiology techniques, including culture-dependent [21][1] techniques. These methods involve the use of normal, oligotrophic, or specialized culture media to count, purify, and identify microbial isolates [16][2]. However, a major challenge in culture-dependent studies is to find suitable culture conditions for the cultivation of different bacterial species [21][1]; in addition, this method provides limited information on community structure [30][3]. Molecular biology techniques have been successfully used in the detection of microorganisms in their environment. Such techniques, based on the detection of nucleic acids, allows the differentiation of microorganisms within complex microbial communities [31][4]. Detection of microorganisms is usually based on the sequences of the small subunit ribosomal RNA (rRNA) genes (16S for prokaryotes) because rRNA genes are highly conserved and contain a level of variability that allows the identification of microorganisms detected by their sequences and the possibility of performing phylogenetic analyses with their closest relatives. A variety of methods have been used to analyze these sequences, including polymerase chain reaction (PCR)-based fingerprinting methods, such as DGGE (denaturing gradient gel electrophoresis) [32[5][6],33], T-RFLP (terminal restriction fragment length polymorphism) [33[6][7],34], clone library construction [35][8], quantitative PCR assays (including those targeting functional genes of interest), sequencing, and the use of stable isotope probing methods [36,37][9][10]. DNA sequencing approaches are very useful for phylogenetic identification [38][11], and more recently, next-generation sequencing (NGS) tools on a variety of platforms, such as Roche FLX 454 pyrosequencing [39][12], Illumina [40[13][14][15],41,42], and SOLiD and Ion Torrent PGM [43[16][17],44], have been applied to the study of cave microorganisms [16][2].
New tools for understanding the microbial world have been provided by culture-independent methods [45][18], such as metagenomics, metaproteomics, metatranscriptomics, and metabolomics, which are fundamental for fully identifying microbial diversity and recognizing its interactions with biotic and abiotic factors [38][11]. Metagenomics approaches, as functional sequence-based analyses of the collective microbial genomes contained in an environmental sample [46][19], have also evolved in recent years. In the classical metagenomic approach, environmental DNA was cloned into vectors using ultracompetent host strains. The resulting clone libraries were then screened for either specific marker genes (sequence-driven approach) or metabolic functions (function-driven approach) [47][20]. Currently, metagenomics typically involves two specific sequencing strategies: amplicon sequencing, most commonly of the 16S rRNA gene as a phylogenetic markers, or shotgun sequencing, which captures the full range of DNA in a sample [41,43,48][14][16][21]. Typically, 16S rRNA gene amplicon sequencing is limited to taxonomic classification at the genus level, depending on the database and classifiers used, and provides limited functional information [49][22]. Shotgun metagenomics provides a more robust and reliable assessment of microbial diversity and has the advantage of classifying bacteria at the species and strain level. It also allows the functional relationships between hosts and bacteria to be studied by directly determining the functional content of samples and allows the exploration of previously unknown microbial life that would otherwise remain unclassified. However, the relatively high cost of shotgun metagenomics and more challenging bioinformatics have prevented its widespread use for microbiome analysis [41,43][14][16].
Rausch et al. 2019 [41][14] presented a study to systematically compare the experimental and analytical aspects of the two main technical approaches for microbial community characterization: 16S rRNA gene amplicon (variable regions V1, V2 and V3, V4) and shotgun sequencing. In addition, for each region, a one-step fusion PCR was compared with a two-step procedure, resulting in five different sequence profiles for each sample. The many aspects of bacterial community characterization are consistent when analyzed by different methods.
In another case, an investigation of the taxonomic composition of microorganisms in the Manao Pee Cave soil using high throughput metagenomic sequencing showed results consistent with the 16S rRNA study based on community structure. The shotgun metagenomic sequencing confirmed that Actinobacteria and Proteobacteria were the dominant bacterial phyla in the Manao Pee Cave community. Shotgun metagenomic sequencing provided higher resolution, allowing the detection of more microbial taxonomic profiles than 16S rRNA sequencing, especially of rare microorganisms. For example, at the family level, 123 bacterial families were identified by shotgun sequencing, but only 55 families were detected by amplicon sequencing [43][16].
To study the biodiversity, activity, and biodeterioration of the microbial populations thriving in the Escoural Cave (Portugal), NGS analyses were performed in different areas of the cave, revealing a predominant distribution of Proteobacteria (58%), Actinobacteria (19%), Firmicutes (7%), Acidobacteria (4%), Bacteroidetes (2%), Gemmatimonadetes (2%), Planctomycetes (2%), and Chloroflexi (1%) [50][23]. Miller et al. (2022) [4][24] analyzed DNA samples isolated from the Atacama Desert (Chile). The first (preliminary) microbiological results confirmed the presence of halophilic microorganisms, such as Salinisphaera sp. and Haloparvum sp., as well as other genera commonly found in saline environments, including Acinetobacter and Pseudomonas.
The identification and study of microorganisms in caves allows us to understand which species are in the majority and what roles they play in the diversity of these environments. Culture-independent methodologies are very useful in this identification, as they allow for a screening of all microorganisms present in a sample. The culture-dependent methods are interesting in the individual study of microorganisms, allowing their isolation for studies of metabolism and the production of compounds with bioactivity.

2. Microorganisms with Bioactivity

Pristine environments preserve large numbers of unstudied bacterial strains with specific metabolic pathways [20][25]. The unique characteristics of these environments give microorganisms the capacity to develop specific metabolisms and to produce new bioactive compounds with potential activities, such as antimicrobial, antifungal, antiviral, and anticancer [9][26].
In recent years, several strains isolated from this ecosystems have been proposed as new species based on a polyphasic taxonomic approach comprising chemotaxonomic, phylogenetic morphological, and physiological characterization, such as strain PO-11 (Arthrobacter cavernae sp. nov.) isolated from Karst cave sediments, Guizhou Province, China [51][27], strain MM109 (Streptomyces lunaelactis sp. nov.) isolated from moonmilk deposit from the cave ‘Grotte des Collemboles’, Belgium [52][28], strain SG1 (Streptosporangium becharense sp. nov.) isolated in a Saharan soil sample collected from Algeria [3][29], strain AG31 (Arthrobacter psychrophenolicus sp. nov.) isolated in an Alpine ice cave, Austria [53][30], among many others. For instance, other bacteria showing important biological activities have also been proposed as new species, such as strains LM 036 and LM044 (Saccharothrix violacea sp. nov.), identified for the first time in a gold mine cave, Kongju, Korea. These strains exhibit antibacterial activity against Bacillus subtilis, Micrococcus luteus, Staphylococcus aureus, and Streptomyces murinus and exhibit antifungal activity against Aspergillus niger, Candida albicans, and Saccharomyces cerevisiae [54][31]. Additionally, in Pha Tup Cave Forest Park, Nan province, Thailand, Nonomuraea monospora sp. nov. [55][32] was identified for the first time, exhibiting antibacterial activity against Bacillus cereus, methicillin-resistant Staphylococcus aureus, and Paenibacillus lavae and exhibiting antitumoral activity against KB (human oral epidermoid carcinoma) and NCI-H187 (human small cell lung) cell lines [56][33]. The strain MBRL 251 (Streptomyces hundungensis sp. nov.) isolated from limestone deposit sites, Manipur, India [57][34], showed antibacterial activity against Curvularia oryzae, Fusarium oxysporum, Helminthosporum oryzae, Pyricularia oryzae, Rhizoctonia oryzae-sativae, and Rhizoctonia solani [58][35].
NGS and field emission scanning electron microscopy were often used for bacterial characterization. For example, in the identification and the functional and morphological characterization in the lava tube cave, Fuente de la Canaria Cave, La Palma Island, was revealed a predominant abundance of Proteobacteria (37–89%), followed by Actinobacteria, Acidobacteria, and Candidatus Rokubacteria. In this study, the ecological role of the microbial communities was also predicted using bioinformatics software that estimated the functional profile from the 16S rRNA gene data, which obtained and predicted the metabolic pathways and enzymes involved in nitrogen, sulfur, methane cycles, and CO2 fixation [59][36].
There are many other studies that report microorganisms from pristine environments with important biological activity. Table 1 outlines the bioactivity of various bacterial species from pristine environments. Most of these studies describe bacteria of the phylum Proteobacteria, Bacteroidetes, Firmicutes, and mainly, Actinobacteria.

2.1. Proteobacteria

Proteobacteria, the largest and most phenotypically diverse phylum, are Gram-negative bacteria [60][37] and one of the most abundant phyla in caves [19,61][38][39].

2.2. Bacteroidetes

Microorganisms of this type are phenotypically diverse, aerobic or facultatively anaerobic chemoorganotrophs, often producing carotenoids and/or flexirubin, which confer yellow or orange colony coloration [27][40].

2.3. Firmicutes

The most members of Firmicutes Phylum are Gram-positive, with low content of guanine and cytosine (G + C) in their genome [62,63][41][42]. The phylum is phenotypically diverse [64][43] and is one of the least robust taxonomic groups, with the taxonomic hierarchy of this phylum remaining weak [62][41]. Cells may be spherical, may have straight, curved, and helical rods or filaments, and may be with or without flagella and with or without heat-resistant endospores [64][43]. Firmicutes are abundant in soil and aquatic environments, where they participate in the decomposition and recycling of organic matter [62][41].

2.4. Actinobacteria

Actinobacteria are Gram-positive filamentous bacteria with a high content of guanine and cytosine (G + C) in their genome. They grow by a combination of tip elongation and hyphal branching [65][44]. Most Actinobacteria are saprophytic soil-dwelling organisms that spend most of their life cycle as semidormant spores, especially under nutrient-limited conditions. They are more abundant in soil than in other environments, especially in alkaline and organic soils, where they form a significant part of the microbial population and are found both on the surface and more than 2 m underground. However, the family has adapted to very different ecological environments: actinomycetes are also found in fresh and salt water and in air [65][44]. Actinobacteria are particularly known for their potential to produce bioactive compounds, such as antibiotics, antimetabolites, and antitumor agents, with the genus Streptomyces having the greatest potential [15][45]. Approximately 45% of known bioactive compounds are secreted by Actinobacteria, of which 85% originate from the Streptomyces genus [66][46]. Actinobacteria are the most studied in the search for bioactive compounds. Members of Actinobacteria are reported to be a dominant microbial population in several cave ecosystems.
In Shuanghe Cave, China, the dominant phylum was Actinobacteria (42.13–48.03%) [30][3]. In Helmcken Falls cave in Canada (volcanic cave), 400 sample were collected from rocks, wall, sediment, and speleothems inside of cave. Isolates were screened, and most of the tested cave actinomycetes demonstrated antimicrobial activities. The results show that bacteria can be the source of novel compounds that provide precursors of new drugs to combat Gram-negative antibiotic resistant bacteria. This study also suggests a high possibility of finding new antimicrobial agents from previously unknown actinomycetes in volcanic cave habitats [11][47]. Yücel and Yamaç (2010) [67][48] isolated 180 actinomycete from Turkish karstic and tested for antimicrobial activity, where 27% exhibited activity only against Gram-negative bacteria and 33% against Gram-positive bacteria. Active cave isolate ratios against overall bacteria, yeasts, and filamentous fungi were determined as 15%, 19%, and 15%, respectively. In another case, in Belgium, different genera (Agromyces, Amycolatopsis, Kocuria, Micrococcus, Micromonospora, Nocardia, Streptomyces, and Rhodococcus) were isolated from cave milk deposits, and 87% of the bacteria showed activity against Gram-positive and 59% against Gram-negative bacteria [68][49].
Gonzalez-Pimentel et al. (2022) [42][15] reported the isolation of two strains of the genus Crossiella, likely representing a new species, isolated from the Altamira Cave, Spain. In vitro and in silico analyses showed the inhibition of pathogenic Gram-positive and Gram-negative bacteria and fungi, as well as the taxonomic distance of both strains from their closest relative, Crossiella cryophile.
Table 1.
Studies of bioactivity of bacteria from pristine environments.
Phylum Microorganism Activity Source Reference
Actinobacteria Actinocorallia aurantiaca Antibacterial (Paenibacillus lavae) Phanangkoi Cave, Thailand [69][50]
Actinoplanes brasiliensis Antibacterial (Staphylococcus aureus) Shuanghe Cave, China [30][3]
Actinoplanes friuliensis Antibacterial (Escherichia coli and S. aureus) and Antifungal (Botrytis cinerea) Shuanghe Cave, China [30][3]
Agromyces subbeticus Antibacterial (E. coli and S. aureus) and Antifungal (B. Cinerea) Shuanghe Cave, China [30][3]
Arthrobacter psychrolactophilus B7 Antibacterial (S. aureus, E. coli, Enterobacter cloacae, Pseudomonas CN11, Pseudomonas aeruginosa, and MRSA) Scarisoara Ice Cave, Romania [70][51]
Arthrobacter sp. R-36193 Antibacterial (P. aeruginosa) and Antifungal (Rhodotorula. mucilaginosa) Magura Cave, Bulgaria [19][38]
Arthrobacter sp. R4 Antibacterial (P. Aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Crossiella sp. Antibacterial (B. cereus, S. aureus, E. coli, P. aeruginosa, and Acinetobacter baumannii) and Antifungal (Aspergillus versicolor, Penicillium chrysogenum, Cladosporium cladosporioides, Fusarium solani, and Ochroconis lascauxensis) Altamira Cave, Spain [42][15]
Dietzia natronolimnaea 44860 Antibacterial (S. aureus, E. coli, E. cloacae, Psudomonas CN11, MRSA, Enterococcus falcium, and Klebsiella 19094) Scarisoara Ice Cave, Romania [70][51]
Microbacterium ginsengiterrae DCY37 Antibacterial (S. aureus, E. coli, E. cloacae, Psudomonas CN11, MRSA, and E. falcium) Scarisoara Ice Cave, Romania [70][51]
Microbacterium pygmaeum KV-490 Antibacterial (S. aureus, E. coli, E. cloacae, Psudomonas CN11, MRSA, E. falcium, and Klebsiella 19094) Scarisoara Ice Cave, Romania [70][51]
Micrococcus luteus CJ-G-TSA7 Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Micromonospora carbonacea Antibacterial (E. coli and S. aureus) and Antifungal (B. cinerea) Shuanghe Cave, China [30][3]
Micromonospora chersinia Antibacterial (B. cereus and P. lavae) and Anticancer (MCF7 and NCI-H187 cell lines) Phanangkoi Cave, Thailand [69][50]
Micromonospora sagamiensis Antibacterial (E. coli and S. aureus) Shuanghe Cave, China [30][3]
Nocardia sungurluensis Antifungal (B. cinerea) Shuanghe Cave, China [30][3]
Nocardioides albus Antibacterial (S. aureus) Shuanghe Cave, China [30][3]
Nonomuraea roseola Antibacterial (B cereus, MRSA, and P. lavae) and Anticancer (NCI-H187 and KB cell lines) Phanangkoi Cave, Thailand [69][50]
Pseudarthrobacter polychromogenes 20136 Antibacterial (S. aureus, E. coli, E. cloacae, P. aeruginosa, Pseudomonas CN11, and MRSA) Scarisoara Ice Cave, Romania [70][51]
Saccharothrix texasensis Anticancer (NCI-H187 and KB cell lines) Phanangkoi Cave, Thailand [69][50]
Spirillospora albida Antibacterial (B. cereus, MRSA, and P. lavae) and Anticancer (NCI-H187 cell line) Phanangkoi Cave, Thailand [69][50]
Streptomyces alboflavus Antifungal (B. cinerea) Shuanghe Cave, China [30][3]
Streptomyces albogriseolus Antibacterial (S. aureus) Shuanghe Cave, China [30][3]
Streptomyces albus Antibacterial (E. coli) Shuanghe Cave, China [30][3]
Streptomyces anulatus Antibacterial (S. aureus) Shuanghe Cave, China [30][3]
Streptomyces aurantiacus Antibacterial (E.coli, S. aureus, and P. aeruginosa) Kotumsar Cave, India [71][52]
Streptomyces avidinii Antibacterial (Salmonella typhimurium, S. aureus, E. coli, P. aeruginosa, Listeria monocytogenes, and Listeria innocua) 12 Portuguese volcanic caves, Terceira Island, Azores [72][53]
Streptomyces flavofungini Antibacterial (S. aureus) and Antifungal (B. cinerea) Shuanghe Cave, China [30][3]
Streptomyces longisporoflavus Antibacterial (E. coli, S. aureus, and P. aeruginosa) Kotumsar Cave, India [71][52]
Streptomyces luridus Antibacterial (E. coli and S. aureus) Kotumsar Cave, India [71][52]
Streptomyces mauvecolor Antibacterial (Proteus sp., S. typhimurium, S. aureus, E. coli, P. aeruginosa, L. monocytogenes, and L. innocua) 12 Portuguese volcanic caves, Terceira Island, Azores [72][53]
Streptomyces nojiriensis Antibacterial (Proteus sp. and E. coli) 12 Portuguese volcanic caves, Terceira Island, Azores [72][53]
Streptomyces olivaceus Antibacterial (E. coli and S. aureus) and Antifungal (B. cinerea) Shuanghe Cave, China [30][3]
Streptomyces prasinosporus Antibacterial (E. coli and P. aeruginosa) Kotumsar Cave, India [71][52]
Streptomyces roseus Antibacterial (E. coli, S. aureus, and P. aeruginosa) Kotumsar Cave, India [71][52]
Streptomyces sp. 82293 Antibacterial (M. luteus and S. aureus) Volcanic cave, Canada [73][54]
Streptomyces spiroverticillatus Antibacterial (S. typhimurium, S. aureus, E. coli, P. aeruginosa, L. monocytogenes, and L. innocua) 12 Portuguese volcanic caves, Terceira Island, Azores [72][53]
Streptomyces yanii Antibacterial (S. aureus) and Antifungal (B. cinerea) Shuanghe Cave, China [30][3]
Proteobacterias Acinetobacter sp. CJ-S-PYD4 Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Candidimonas bauzanensis BZ59 Antibacterial (S. aureus, E. coli, E. cloacae, Pseudomonas CN11, P. aeruginosa, and MRSA) Scarisoara Ice Cave, Romania [70][51]
Caulobacter henricii 15253 Antibacterial (S. aureus, E. coli, E. cloacae, Pseudomonas CN11, P. aeruginosa, and MRSA) Scarisoara Ice Cave, Romania [70][51]
Comamonas sp. BM-9_6 Antibacterial (B. subtilis, X. oryzae, and P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Delftia acidovorans 14950 Antibacterial (S. aureus, E. coli, E. cloacae, Pseudomonas CN11, P. aeruginosa, MRSA, and Klebsiella 19094) Scarisoara Ice Cave, Romania [70][51]
Micrococcus luteus Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Obesumbacterium proteus Antibacterial (P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas brenneri 97-391 Antibacterial (S. aureus, E. cloacae, Pseudomonas CN11, P. aeruginosa, and MRSA) Scarisoara Ice Cave, Romania [70][51]
Pseudomonas fluorescens Antibacterial (P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas fluorescens 15834 Antibacterial (Xanthomonas oryzae and P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas fluorescens LMG 14576 Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas fragi Antibacterial (P. aeruginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas grimontii 97-514 Antibacterial (S. aureus, E. coli, E. cloacae, Pseudomonas CN11, P. aeruginosa, MRSA, Klebsiella 19094, and E. falcium) Scarisoara Ice Cave, Romania [70][51]
Pseudomonas kilonensis DSM 13647 Antibacterial (B. subtilis) Yumugi River cave, New Guinea [61][39]
Pseudomonas migulae NBRC 103157 Antibacterial (B. subtilis and P. aeruginosa) Yumugi River cave, New Guinea [61][39]
Pseudomonas plecoglossicida Antibacterial (B. subtilis, X. oryzae, and P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas putida Antibacteral (B. subtilis and X. oryzae) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas resinovorans ATCC 14235 Antibacterial (B. subtilis) Yumugi River cave, New Guinea [61][39]
Pseudomonas sp. Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Serratia proteamaculans Antibacterial (P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Serratia sp. Antibacterial (B. subtilis, X. oryzae, and P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Serratia sp. 136-2 Antibacterial (P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Serratia sp. L0305 Antibacterial (P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Stenotrophomonas sp. Antibacterial (P. aeruginosa) Magura Cave, Bulgaria [19][38]
Stenotrophomonas sp. DIC6JA Antibacterial (P. aeruginosa) Magura Cave, Bulgaria [19][38]
Pseudomonas sp. Antibacterial (S. aureus) Kadıini Cave, Turkey [13][55]
Bacteroidetes Myroides sp. IT-2012 Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Sphingobacterium sp. Antibacterial (X. oryzae and P. aeruginosa) and Antifungal (R. mucilaginosa) Magura Cave, Bulgaria [19][38]
Sphingobacterium sp. Ag8 Antibacterial (P. aeruginosa) Magura Cave, Bulgaria [19][38]
Firmicutes Bacillus amyloliquefaciens Antibacterial (P. aeruginosa) Magura Cave, Bulgaria [19][38]
Bacillus cereus Antibacterial (S. epidermidis, B. subtilis) Kadıini Cave, Turkey [13][55]
Bacillus eiseniae Antibacterial (S. aureus) Cave in the Hindu Kush Mountain, Pakistain [39][12]
Bacillus humi Antibacterial (S. typhi) Cave in the Hindu Kush Mountain, Pakistain [39][12]
Bacillus sp. Antibacterial (S. aureus JE2 and S. aureus SH1000) Rogers Belmont Cave, USA [74][56]
Bacillus sp. Antibacterial (B. subtilis) Kadıini Cave, Turkey [13][55]
Bacillus thuringiensis Antibacterial (S. epidermidis and B. subtilis) Kadıini Cave, Turkey [13][55]
Bacillus toyonensis BCT-7112 Antibacterial (S. aureus, E. cloacae, Pseudomonas CN11, P. aeruginosa, and MRSA) Scarisoara Ice Cave, Romania [70][51]
Bacillus weihenstephanensis Antibacterial (S. epidermidis and B. subtilis) Kadıini Cave, Turkey [13][55]
Brevibacillus borstelensis Antifungal (C. albicans) Cave in the Hindu Kush Mountain, Pakistain [39][12]
Brevibacterium frigoritolerans Antibacterial (S. epidermidis and B. subtilis) Kadıini Cave, Turkey [13][55]
Fictibacillus nanhaiensis Antibacterial (S. typhi and S. aureus) Cave in the Hindu Kush Mountain, Pakistain [39][12]
While many studies have been conducted to identify bioactivity in cave bacteria, some of them do not identify the compounds that have activity. This can be due to a variety of reasons, such as the complexity of the microbial community in caves or the limitations of the analytical techniques used. However, identifying the specific compounds that have activity is crucial for further research and development of potential applications. It would be beneficial for future studies to focus on identifying and characterizing the bioactive compounds produced by cave bacteria, as this can lead to a better understanding of their potential uses and applications.

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