Editorial

4 pages, 214 KiB

Open AccessEditorial

Special Issue “Halophilic Microorganisms”

by Cristina Sánchez-Porro

Microorganisms 2023, 11(3), 690; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms11030690 - 08 Mar 2023

Cited by 1 | Viewed by 1175

Hypersaline environments are mainly represented by aquatic systems, such as solar salt ponds or natural salt lakes, as well as by the sediments of these hypersaline aquatic ecosystems and soils with high salt content [...] Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

Research

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19 pages, 4323 KiB

Open AccessArticle

Morphological Phenotypes, Cell Division, and Gene Expression of Escherichia coli under High Concentration of Sodium Sulfate

by Khanh Nguyen and Pradeep Kumar

Microorganisms 2022, 10(2), 274; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10020274 - 25 Jan 2022

Cited by 7 | Viewed by 3343

Abstract

Sodium and sulfate ions are among the suggested abundant ions on Europa, a moon of Jupiter. In order to investigate the potential habitability of Europa, we study the effects of sodium sulfate (Na₂SO₄) on a non-halophilic bacterium by subjecting [...] Read more.

Sodium and sulfate ions are among the suggested abundant ions on Europa, a moon of Jupiter. In order to investigate the potential habitability of Europa, we study the effects of sodium sulfate (Na₂SO₄) on a non-halophilic bacterium by subjecting Escherichia coli (E. coli) to a wide range of Na₂SO₄ concentrations (0–1.0 m). We discover that, as the concentration of sodium sulfate increases, the biomass doubling time increases and the cell growth is completely inhibited at

1.0

m Na₂SO₄. Furthermore, we find that E. coli exhibits three distinct morphological phenotypes—(i) shortened, (ii) normal, and (iii) elongated/filamented cells at

0.6

m and

0.8

m Na₂SO₄. We have examined the expression of different genes involved in sodium and sulfate transport (nhaA, nhaB, cysZ, sbp), osmotically driven transport of water (aqpZ), sulfate metabolism (cysN), fatty acid production (fabA), and a global transcriptional regulator (osmZ). Our results suggest that the expression of these genes is not affected significantly at high concentrations of sodium sulfate in the exponential growth phase. Using our experimental data and the existing data in the literature, we show that the osmotic pressure difference may play a major role in determining the growth inhibition of E. coli and B. subtilis at high concentrations of salt. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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14 pages, 2140 KiB

Open AccessArticle

Biomineralization by Extremely Halophilic and Metal-Tolerant Community Members from a Sulfate-Dominated Metal-Rich Environment

by Marie Harpke, Sebastian Pietschmann, Flávio Silva Costa, Clara Gansert, Falko Langenhorst and Erika Kothe

Microorganisms 2022, 10(1), 79; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10010079 - 31 Dec 2021

Cited by 12 | Viewed by 1982

Abstract

The adaptation to adverse environmental conditions can lead to adapted microbial communities that may be screened for mechanisms involved in halophily and, in this case, metal tolerance. At a former uranium mining and milling site in Seelingstädt, Germany, microbial communities from surface waters [...] Read more.

The adaptation to adverse environmental conditions can lead to adapted microbial communities that may be screened for mechanisms involved in halophily and, in this case, metal tolerance. At a former uranium mining and milling site in Seelingstädt, Germany, microbial communities from surface waters and sediment soils were screened for isolates surviving high salt and metal concentrations. The high salt contents consisted mainly of chloride and sulfate, both in soil and riverbed sediment samples, accompanied by high metal loads with presence of cesium and strontium. The community structure was dominated by Chloroflexi, Proteobacteria and Acidobacteriota, while only at the highest contaminations did Firmicutes and Desulfobacterota reach appreciable percentages in the DNA-based community analysis. The extreme conditions providing high stress were mirrored by low numbers of cultivable strains. Thirty-four extremely halotolerant bacteria (23 Bacillus sp. and another 4 Bacillales, 5 Actinobacteria, and 1 Gamma-Proteobacterium) surviving 25 to 100 mM SrCl₂, CsCl, and Cs₂SO₄ were further analyzed. Mineral formation of strontium- or cesium-struvite could be observed, reducing bioavailability and thereby constituting the dominant metal and salt resistance strategy in this environment. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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12 pages, 2356 KiB

Open AccessArticle

Characterization of the Proteolytic Activity of a Halophilic Aspergillus reticulatus Strain SK1-1 Isolated from a Solar Saltern

by Dawoon Chung, Woon-Jong Yu, Ji-Yeon Lim, Nam-Seon Kang, Yong-Min Kwon, Grace Choi, Seung-Sub Bae, Kichul Cho and Dae-Sung Lee

Microorganisms 2022, 10(1), 29; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10010029 - 24 Dec 2021

Cited by 9 | Viewed by 3188

Abstract

Salterns are hypersaline environments that are inhabited by diverse halophilic microorganisms, including fungi. In this study, we isolated a fungal strain SK1-1 from a saltern in the Republic of Korea, which was identified as Asperillus reticulatus. This is the first reported saline-environment-derived [...] Read more.

Salterns are hypersaline environments that are inhabited by diverse halophilic microorganisms, including fungi. In this study, we isolated a fungal strain SK1-1 from a saltern in the Republic of Korea, which was identified as Asperillus reticulatus. This is the first reported saline-environment-derived A. reticulatus that belongs to the Aspergillus penicillioides clade and encompasses xerophilic fungi. SK1-1 was halophilic, obligately requiring NaCl for growth, with a maximum radial growth of 6%–9% (w/v) NaCl. To facilitate the biotechnological application of halophilic fungi, we screened the SK1-1 strain for proteolytic activity. Proteases have widespread applications in food processing, detergents, textiles, and waste treatment, and halophilic proteases can enable protein degradation in high salt environments. We assessed the proteolytic activity of the extracellular crude enzyme of SK1-1 using azocasein as a substrate. The crude protease exhibited maximum activity at 40–50 °C, pH 9.5–10.5, and in the absence of NaCl. It was also able to retain up to 69% of its maximum activity until 7% NaCl. Protease inhibitor assays showed complete inhibition of the proteolytic activity of crude enzymes by Pefabloc^® SC. Our data suggest that the halophilic A. reticulatus strain SK1-1 produces an extracellular alkaline serine protease. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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16 pages, 2503 KiB

Open AccessArticle

Taxogenomic and Metabolic Insights into Marinobacterium ramblicola sp. nov., a New Slightly Halophilic Bacterium Isolated from Rambla Salada, Murcia

by Ana Durán-Viseras, David J. Castro, José Carlos Reina, Victoria Béjar and Fernando Martínez-Checa

Microorganisms 2021, 9(8), 1654; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9081654 - 03 Aug 2021

Cited by 9 | Viewed by 2632

Abstract

A Gram-negative, motile, rod-shaped bacteria, designated D7^T, was isolated by using the dilution-to-extinction method, from a soil sample taken from Rambla Salada (Murcia, Spain). Growth of strain D7^T was observed at 15–40 °C (optimum, 37 °C), pH 5–9 (optimum, 7) [...] Read more.

A Gram-negative, motile, rod-shaped bacteria, designated D7^T, was isolated by using the dilution-to-extinction method, from a soil sample taken from Rambla Salada (Murcia, Spain). Growth of strain D7^T was observed at 15–40 °C (optimum, 37 °C), pH 5–9 (optimum, 7) and 0–7.5% (w/v) NaCl (optimum, 3%). It is facultatively anaerobic. Phylogenetic analysis based on 16S rRNA gene sequence showed it belongs to the genus Marinobacterium. The in silico DDH and ANI against closest Marinobacterium relatives support its placement as a new species within this genus. The major fatty acids of strain D7^T were C_16:0, summed feature 3 (C_16:1 ω7c/C_16:1 ω6c) and summed feature 8 (C_18:1 ω7c/C_18:1 ω6c). The polar lipid profile consists of phosphatidylethanolamine, phosphatidylglycerol and two uncharacterized lipids. Ubiquinone 8 was the unique isoprenoid quinone detected. The DNA G + C content was 59.2 mol%. On the basis of the phylogenetic, phenotypic, chemotaxonomic and genomic characterization, strain D7^T (= CECT 9818^T = LMG 31312^T) represents a novel species of the genus Marinobacterium for which the name Marinobacterium ramblicola sp. nov. is proposed. Genome-based metabolic reconstructions of strain D7^T suggested a heterotrophic and chemolitotrophic lifestyle, as well as the capacity to biosynthetize and catabolize compatible solutes, and to degrade hydrocarbon aromatic compounds. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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18 pages, 3217 KiB

Open AccessArticle

Prokaryotic Communities in the Thalassohaline Tuz Lake, Deep Zone, and Kayacik, Kaldirim and Yavsan Salterns (Turkey) Assessed by 16S rRNA Amplicon Sequencing

by Can Akpolat, Ana Beatriz Fernández, Pinar Caglayan, Baris Calli, Meral Birbir and Antonio Ventosa

Microorganisms 2021, 9(7), 1525; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9071525 - 17 Jul 2021

Cited by 9 | Viewed by 3121

Abstract

Prokaryotic communities and physico-chemical characteristics of 30 brine samples from the thalassohaline Tuz Lake (Salt Lake), Deep Zone, Kayacik, Kaldirim, and Yavsan salterns (Turkey) were analyzed using 16S rRNA amplicon sequencing and standard methods, respectively. Archaea (98.41% of reads) was found to dominate [...] Read more.

Prokaryotic communities and physico-chemical characteristics of 30 brine samples from the thalassohaline Tuz Lake (Salt Lake), Deep Zone, Kayacik, Kaldirim, and Yavsan salterns (Turkey) were analyzed using 16S rRNA amplicon sequencing and standard methods, respectively. Archaea (98.41% of reads) was found to dominate in these habitats in contrast to the domain Bacteria (1.38% of reads). Representatives of the phylum Euryarchaeota were detected as the most predominant, while 59.48% and 1.32% of reads, respectively, were assigned to 18 archaeal genera, 19 bacterial genera, 10 archaeal genera, and one bacterial genus that were determined to be present, with more than 1% sequences in the samples. They were the archaeal genera Haloquadratum, Haloarcula, Halorhabdus, Natronomonas, Halosimplex, Halomicrobium, Halorubrum, Halonotius, Halolamina, Halobacterium, and Salinibacter within the domain Bacteria. The genera Haloquadratum and Halorhabdus were found in all sampling sites. While Haloquadratum, Haloarcula, and Halorhabdus were the most abundant genera, two uncultured Tuz Lake Halobacteria (TLHs) 1 and 2 were detected in high abundance, and an additional uncultured haloarchaeal TLH-3 was found as a minor abundant uncultured taxon. Their future isolation in pure culture would permit us to expand our knowledge on hypersaline thalassohaline habitats, as well as their ecological role and biomedical and biotechnological potential applications. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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16 pages, 1476 KiB

Open AccessArticle

The Survival of Haloferax mediterranei under Stressful Conditions

by Laura Matarredona, Mónica Camacho, Basilio Zafrilla, Gloria Bravo-Barrales, Julia Esclapez and María-José Bonete

Microorganisms 2021, 9(2), 336; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms9020336 - 08 Feb 2021

Cited by 11 | Viewed by 3351

Abstract

Haloarchaea can survive and thrive under exposure to a wide range of extreme environmental factors, which represents a potential interest to biotechnology. Growth responses to different stressful conditions were examined in the haloarchaeon Haloferax mediterranei R4. It has been demonstrated that this halophilic [...] Read more.

Haloarchaea can survive and thrive under exposure to a wide range of extreme environmental factors, which represents a potential interest to biotechnology. Growth responses to different stressful conditions were examined in the haloarchaeon Haloferax mediterranei R4. It has been demonstrated that this halophilic archaeon is able to grow between 10 and 32.5% (w/v) of sea water, at 32–52 °C, although it is expected to grow in temperatures lower than 32 °C, and between 5.75 and 8.75 of pH. Moreover, it can also grow under high metal concentrations (nickel, lithium, cobalt, arsenic), which are toxic to most living beings, making it a promising candidate for future biotechnological purposes and industrial applications. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) analysis quantified the intracellular ion concentrations of these four metals in Hfx. mediterranei, concluding that this haloarchaeon can accumulate Li⁺, Co²⁺, As⁵⁺, and Ni²⁺ within the cell. This paper is the first report on Hfx. mediterranei in which multiple stress conditions have been studied to explore the mechanism of stress resistance. It constitutes the most detailed study in Haloarchaea, and, as a consequence, new biotechnological and industrial applications have emerged. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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16 pages, 1958 KiB

Open AccessArticle

Bioprospecting for Novel Halophilic and Halotolerant Sources of Hydrolytic Enzymes in Brackish, Saline and Hypersaline Lakes of Romania

by Robert Ruginescu, Ioana Gomoiu, Octavian Popescu, Roxana Cojoc, Simona Neagu, Ioana Lucaci, Costin Batrinescu-Moteau and Madalin Enache

Microorganisms 2020, 8(12), 1903; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms8121903 - 30 Nov 2020

Cited by 40 | Viewed by 3894

Abstract

Halophilic and halotolerant microorganisms represent promising sources of salt-tolerant enzymes that could be used in various biotechnological processes where high salt concentrations would otherwise inhibit enzymatic transformations. Considering the current need for more efficient biocatalysts, the present study aimed to explore the microbial [...] Read more.

Halophilic and halotolerant microorganisms represent promising sources of salt-tolerant enzymes that could be used in various biotechnological processes where high salt concentrations would otherwise inhibit enzymatic transformations. Considering the current need for more efficient biocatalysts, the present study aimed to explore the microbial diversity of five under- or uninvestigated salty lakes in Romania for novel sources of hydrolytic enzymes. Bacteria, archaea and fungi were obtained by culture-based approaches and screened for the production of six hydrolases (protease, lipase, amylase, cellulase, xylanase and pectinase) using agar plate-based assays. Moreover, the phylogeny of bacterial and archaeal isolates was studied through molecular methods. From a total of 244 microbial isolates, 182 (74.6%) were represented by bacteria, 22 (9%) by archaea, and 40 (16.4%) by fungi. While most bacteria synthesized protease and lipase, the most frequent hydrolase produced by fungi was pectinase. The archaeal isolates had limited hydrolytic activity, being able to produce only amylase and cellulase. Among the taxonomically identified isolates, the best hydrolytic activities were observed in halotolerant bacteria belonging to the genus Bacillus and in extremely halophilic archaea of the genera Haloterrigena and Halostagnicola. Therefore, the present study highlights that the investigated lakes harbor various promising species of microorganisms able to produce industrially valuable enzymes. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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Review

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19 pages, 3506 KiB

Open AccessReview

Recent Antimicrobial Responses of Halophilic Microbes in Clinical Pathogens

by Henciya Santhaseelan, Vengateshwaran Thasu Dinakaran, Hans-Uwe Dahms, Johnthini Munir Ahamed, Santhosh Gokul Murugaiah, Muthukumar Krishnan, Jiang-Shiou Hwang and Arthur James Rathinam

Microorganisms 2022, 10(2), 417; https://0-doi-org.brum.beds.ac.uk/10.3390/microorganisms10020417 - 11 Feb 2022

Cited by 10 | Viewed by 3817

Abstract

Microbial pathogens that cause severe infections and are resistant to drugs are simultaneously becoming more active. This urgently calls for novel effective antibiotics. Organisms from extreme environments are known to synthesize novel bioprospecting molecules for biomedical applications due to their peculiar characteristics of [...] Read more.

Microbial pathogens that cause severe infections and are resistant to drugs are simultaneously becoming more active. This urgently calls for novel effective antibiotics. Organisms from extreme environments are known to synthesize novel bioprospecting molecules for biomedical applications due to their peculiar characteristics of growth and physiological conditions. Antimicrobial developments from hypersaline environments, such as lagoons, estuaries, and salterns, accommodate several halophilic microbes. Salinity is a distinctive environmental factor that continuously promotes the metabolic adaptation and flexibility of halophilic microbes for their survival at minimum nutritional requirements. A genetic adaptation to extreme solar radiation, ionic strength, and desiccation makes them promising candidates for drug discovery. More microbiota identified via sequencing and ‘omics’ approaches signify the hypersaline environments where compounds are produced. Microbial genera such as Bacillus, Actinobacteria, Halorubrum and Aspergillus are producing a substantial number of antimicrobial compounds. Several strategies were applied for producing novel antimicrobials from halophiles including a consortia approach. Promising results indicate that halophilic microbes can be utilised as prolific sources of bioactive metabolites with pharmaceutical potentialto expand natural product research towards diverse phylogenetic microbial groups which inhabit salterns. The present study reviews interesting antimicrobial compounds retrieved from microbial sources of various saltern environments, with a discussion of their potency in providing novel drugs against clinically drug-resistant microbes. Full article

(This article belongs to the Special Issue Halophilic Microorganisms)

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