{{Short description|Adaptation of living organisms to conditions of high salinity}} '''Halotolerance''' is the ability of organisms to live in salt concentrations beyond which is necessary for their growth.<ref name=":0">{{Citation |last=Antón|first=Josefa|title=Halotolerance|date=2011|encyclopedia=Encyclopedia of Astrobiology|pages=727|url=https://link.springer.com/rwe/10.1007/978-3-642-11274-4_695|access-date=2026-02-25|publisher=Springer, Berlin, Heidelberg|language=en|doi=10.1007/978-3-642-11274-4_695|isbn=978-3-642-11274-4|url-access=subscription}}</ref> Halotolerant species are found in saline waters and soils.<ref name=":0" /> Halotolerant microorganisms include bacteria,<ref>{{Cite web |title=Halotolerant - Knowledge and References |url=https://taylorandfrancis.com/knowledge/Engineering_and_technology/Biomedical_engineering/Halotolerant/ |access-date=2026-02-25 |website=Taylor & Francis |language=en-US}}</ref> archaea,<ref>{{Cite journal |last1=Matarredona |first1=Laura |last2=Zafrilla |first2=Basilio |last3=Camacho |first3=Mónica |last4=Bonete |first4=María-José |last5=Esclapez |first5=Julia |date=December 2024 |title=Understanding the tolerance of halophilic archaea to stress landscapes |journal=Environmental Microbiology Reports |volume=16 |issue=6 |article-number=e70039 |doi=10.1111/1758-2229.70039 |issn=1758-2229 |pmc=11578932 |pmid=39568122 |bibcode=2024EnvMR..16E0039M }}</ref> and fungi.<ref name=":1">{{Cite journal |last1=Suryanarayanan |first1=T. S. |last2=Ravishankar |first2=J. P. |date=2023-12-01 |title=They too serve who tolerate and survive: the need to study halotolerant fungi to appreciate their role in saline ecosystems |url=https://www.sciencedirect.com/science/article/pii/S1749461323000349 |journal=Fungal Biology Reviews |volume=46 |article-number=100328 |doi=10.1016/j.fbr.2023.100328 |bibcode=2023FunBR..4600328S |issn=1749-4613|url-access=subscription }}</ref> Halophilic microorganisms require salt to grow;<ref>{{Cite journal |last=Vreeland |first=R. H. |date=1987 |title=Mechanisms of halotolerance in microorganisms |journal=Critical Reviews in Microbiology |volume=14 |issue=4 |pages=311–356 |doi=10.3109/10408418709104443 |issn=1040-841X |pmid=3308318}}</ref> halotolerant organisms may be classified as some degree halophilic, but are often contrasted from halophiles because halotolerant organisms do not require a high-salinity environment.<ref name=":1" /> Halotolerant microorganisms are of considerable biotechnological interest<ref name=":2">{{Cite journal |last=Margesin |first=Rosa |last2=Schinner |first2=Franz |date=2001-04-01 |title=Potential of halotolerant and halophilic microorganisms for biotechnology |url=https://doi.org/10.1007/s007920100184 |journal=Extremophiles |language=en |volume=5 |issue=2 |pages=73–83 |doi=10.1007/s007920100184 |issn=1431-0651|url-access=subscription }}</ref> as their roles in saline ecosystems remains unknown.<ref name=":1" />
==Applications== Fields of scientific research relevant to halotolerance include biochemistry, molecular biology, cell biology, physiology, ecology, and genetics.
Studying the mechanisms of halotolerance in microorganisms can be applied to organism growth and ecosystem dynamics in increasingly saline environments.<ref name=":3">{{Cite journal |last1=Martínez-Espinosa|first1=Rosa María|last2=Kumar|first2=Sumit|last3=DasSarma|first3=Shiladitya|date=2026|title=Editorial: Adaptation of halophilic/halotolerant microorganisms and their applications, volume II|journal=Frontiers in Microbiology|volume=17|article-number=1780220|doi=10.3389/fmicb.2026.1780220|doi-access=free|issn=1664-302X|pmc=12900378|pmid=41695952}}</ref> Halotolerance can be applied to pollution and climate change; processes of halotolerance may be implemented to limit the damages of pollution.<ref name=":3" />
Some halotolerant microorganisms are able to use light energy to generate proton and chloride gradients which allows bioenergetic processes to occur.<ref name=":2" /> The light-transducing protein, bacteriorhodopsin, allows this pathway to occur and has applications in holography, artificial retina, neutral network optical computing, and other technical methods.<ref name=":4">{{Cite web |title=Bacteriorhodopsin - an overview {{!}} ScienceDirect Topics|url=https://www.sciencedirect.com/topics/biochemistry-genetics-and-molecular-biology/bacteriorhodopsin|access-date=2026-02-25|website=www.sciencedirect.com}}</ref>
Halotolerant microorganisms may be utilized as bioremidators in contaminated soils and in waste water.<ref name=":3" /> Certain halotolerant organisms are able to produce biosurfactants in saline environments polluted by hydrocarbons<ref name=":2" /> where other organisms may be unable to survive and produce biosurfactants. Halotlerant bacteria effectively remediate saline soil by lowering the Na contents and sodium absorption ratios in soil and by degrading toxic compounds.<ref>{{Cite web |title=Halotolerant - Knowledge and References|url=https://taylorandfrancis.com/knowledge/Engineering_and_technology/Biomedical_engineering/Halotolerant/|access-date=2026-03-06|website=Taylor & Francis|language=en-US}}</ref>
Fermentation processes in food that use salt can utilize halotolerant organisms. ''Lactobacillus pantarum'' is used in the production of pickles and sauerkraut, and other halotolerant bacteria are used in the production fish sauce and soy sauces.<ref name=":2" />
Goals of studying halotolerance include increasing the agricultural productivity of lands affected by soil salination or where only saline water is available. Salinity limits crop productivity and growth, so conventional agricultural species could be made more halotolerant by gene transfer from naturally halotolerant species (by conventional breeding or genetic engineering) or by applying treatments developed from an understanding of the mechanisms halotolerance.<ref>{{Cite journal |last1=Afzal|first1=Muhammad|last2=Hindawi|first2=Salah El Sayed|last3=Alghamdi|first3=Salem Safer|last4=Migdadi|first4=Hussein H.|last5=Khan|first5=Muhammad Altaf|last6=Hasnain|first6=Muhammad Usama|last7=Arslan|first7=Muhammad|last8=Habib ur Rahman|first8=Muhammad|last9=Sohaib|first9=Muhammad|date=2023-06-01|title=Potential Breeding Strategies for Improving Salt Tolerance in Crop Plants|journal=Journal of Plant Growth Regulation|language=en|volume=42|issue=6|pages=3365–3387|doi=10.1007/s00344-022-10797-w|bibcode=2023JPGR...42.3365A |issn=1435-8107|doi-access=free}}</ref>
Environment stressors like drought and extreme temperatures can involve or induce osmotic changes, so applying knowledge of halotolerance is relevant to environments with extremes in moisture or temperature.<ref>{{Cite journal |last1=Orzoł|first1=Aleksandra|last2=Głowacka|first2=Katarzyna|last3=Pätsch|first3=Ricarda|last4=Piernik|first4=Agnieszka|last5=Gallegos-Cerda|first5=Susana Dianey|last6=Cárdenas-Pérez|first6=Stefany|date=2025-04-16|title=The local environment influences salt tolerance differently in four Salicornia europaea L. inland populations|url=https://www.nature.com/articles/s41598-025-97394-5|journal=Scientific Reports|language=en|volume=15|issue=1|page=13128|doi=10.1038/s41598-025-97394-5|bibcode=2025NatSR..1513128O |issn=2045-2322|pmc=12003738}}</ref>
Bioactive metabolites of halotolerant organisms may limit the growth of cancer, especially lung and breast cancer, and may have applications in chemotherapy resistance and treatment-related toxicity.<ref>{{Cite journal |last1=Fang|first1=Longteng|last2=Xu|first2=Liping|last3=Kader|first3=Marhaba|last4=Ding|first4=Tingting|last5=Lu|first5=Shiyang|last6=Wang|first6=Dong|last7=Sharma|first7=Amit Raj|last8=Zhang|first8=Zhiwei|date=2025-07-24|title=Salt-Adapted Microorganisms: A Promising Resource for Novel Anti-Cancer Drug Discovery|journal=Marine Drugs|volume=23|issue=8|page=296|doi=10.3390/md23080296|doi-access=free|issn=1660-3397|pmc=12387818|pmid=40863613}}</ref>
==Cellular functions of halotolerant organisms== Tolerance of high salt conditions occurs through several physiological mechanisms. High concentrations of salt in soil or water that plants live in can trigger ionic imbalances which cause complications in respiration and photosynthesis, leading to reduced rates of growth, injury and death in severe cases.<ref>{{Cite journal |last1=Shrivastava|first1=Pooja|last2=Kumar|first2=Rajesh|date=March 2015|title=Soil salinity: A serious environmental issue and plant growth promoting bacteria as one of the tools for its alleviation|journal=Saudi Journal of Biological Sciences|volume=22|issue=2|pages=123–131|doi=10.1016/j.sjbs.2014.12.001|issn=1319-562X|pmc=4336437|pmid=25737642}}</ref> To be considered tolerant of saline conditions, the protoplast must show methods of balancing the toxic and osmotic effects of the increased salt concentrations.
Halotolerant organisms must cope with the stress of changing and high salinity;<ref name=":5">{{Cite journal |last1=Zhou|first1=Peng|last2=Bu|first2=Yu-Xin|last3=Xu|first3=Lin|last4=Xu|first4=Xue-Wei|last5=Shen|first5=Hong-Bin|date=2023-03-13|title=Understanding the mechanisms of halotolerance in members of Pontixanthobacter and Allopontixanthobacter by comparative genome analysis|journal=Frontiers in Microbiology|language=English|volume=14|article-number=1111472 |doi=10.3389/fmicb.2023.1111472|doi-access=free|pmid=36992937 |pmc=10040529 |issn=1664-302X}}</ref> osmotic stress and ionic stress is put on cells in high salinity.<ref name=":6">{{Cite journal |last1=Plemenitaš|first1=Ana|last2=Lenassi|first2=Metka|last3=Konte|first3=Tilen|last4=Kejžar|first4=Anja|last5=Zajc|first5=Janja|last6=Gostinčar|first6=Cene|last7=Gunde-Cimerman|first7=Nina|date=2014|title=Adaptation to high salt concentrations in halotolerant/halophilic fungi: a molecular perspective|journal=Frontiers in Microbiology|volume=5|page=199|doi=10.3389/fmicb.2014.00199|doi-access=free|issn=1664-302X|pmc=4017127|pmid=24860557}}</ref> An environment of high salinity leads to loss of water in the cell, so halotolerant organisms have developed mechanisms to retain water and sequester salt within the cell.<ref name=":0" /> Halotolerant organisms may utilize a combination of mechanisms to tolerate high salinity environments.
Halotolerant organisms maintain osmotic balance by producing or accumulating osmoprotectants.<ref name=":5" /> This mechanism allows the cell to retain water in conditions of high salinity by maintaining water uptake without disrupting metabolic cellular processes. In response to high salinity, the rate of transcription of genes for compatible solutes is increased.<ref name=":5" />
In many halotolerant organisms high levels of salt are absorbed by cells to maintain an osmotic potential lower than that of the environment to ensure water uptake. A mechanism of tolerating excessive salt in halotolerant organisms is the sequestration of salt into a vacuole. This keeps the concentration of salt in the cell's cytoplasm low so that the metabolic activities of the cell can continue.<ref>{{Cite journal |last1=Oi|first1=Takao|last2=Clode|first2=Peta L.|last3=Taniguchi|first3=Mitsutaka|last4=Colmer|first4=Timothy D.|last5=Kotula|first5=Lukasz|date=May 2022|title=Salt tolerance in relation to elemental concentrations in leaf cell vacuoles and chloroplasts of a C4 monocotyledonous halophyte|journal=Plant, Cell & Environment|volume=45|issue=5|pages=1490–1506|doi=10.1111/pce.14279|issn=1365-3040|pmc=9305513|pmid=35128687}}</ref>
In some organisms, flagellum-related genes are down-regulated in environments with high concentrations of salt which conserves energy of motion to be used in osmoprotection.<ref>{{Cite journal |last1=Chen|first1=Yan-Huey|last2=Lu|first2=Chia-Wei|last3=Shyu|first3=Yuan-Tay|last4=Lin|first4=Shih-Shun|date=2017-10-12|title=Revealing the Saline Adaptation Strategies of the Halophilic Bacterium Halomonas beimenensis through High-throughput Omics and Transposon Mutagenesis Approaches|url=https://www.nature.com/articles/s41598-017-13450-9|journal=Scientific Reports|language=en|volume=7|issue=1|page=13037|doi=10.1038/s41598-017-13450-9|bibcode=2017NatSR...713037C |issn=2045-2322|pmc=5638851}}</ref>
==Bacterial halotolerance== The extent of halotolerance varies widely amongst different species of bacteria.<ref>Dieter Häussinger and Helmut Sies (2007) ''Osmosensing and Osmosignaling'', Academic Press, 579 pages {{ISBN|0-12-373921-7}}</ref> A number of cyanobacteria are halotolerant, such as the cyanobacteria of Makgadikgadi Pans, a large hypersaline lake in Botswana.<ref>{{Cite journal |last1=Filippidou|first1=Sevasti|last2=Price|first2=Alex|last3=Spencer-Jones|first3=Charlotte|last4=Scales|first4=Anthony|last5=Macey|first5=Michael C.|last6=Franchi|first6=Fulvio|last7=Lebogang|first7=Lesedi|last8=Cavalazzi|first8=Barbara|last9=Schwenzer|first9=Susanne P.|last10=Olsson-Francis|first10=Karen|date=2024-01-11|title=Diversity of Microbial Mats in the Makgadikgadi Salt Pans, Botswana|journal=Microorganisms|volume=12|issue=1|page=147|doi=10.3390/microorganisms12010147|doi-access=free|issn=2076-2607|pmc=10818877|pmid=38257974}}</ref> Cyanobacteria possess a high level of physiological flexibility; recent research on the mechanisms of halotolerance in cyanobacteria using omics approaches aim to identify the gene networks and biochemical pathways of halotolerance like those that produce osmoprotectants.<ref>{{Cite journal |last1=Waditee-Sirisattha|first1=Rungaroon|last2=Kageyama|first2=Hakuto|date=2023-02-01|title=Halotolerance, stress mechanisms, and circadian clock of salt-tolerant cyanobacteria|journal=Applied Microbiology and Biotechnology|language=en|volume=107|issue=4|pages=1129–1141|doi=10.1007/s00253-023-12390-x|pmid=36700967 |issn=1432-0614}}</ref>
== Fungal halotolerance == thumb|''Debaryomyces hansenii'' Before the 2000s, it was commonly believed that fungi did not inhabit extremely saline environments, but research has disproved the idea by finding fungi in solar salterns.<ref name=":7">{{Cite journal |last1=Gunde-Cimerman|first1=Nina|last2=Ramos|first2=Jose|last3=Plemenitaš|first3=Ana|date=2009-11-01|title=Halotolerant and halophilic fungi|url=https://www.sciencedirect.com/science/article/pii/S0953756209001610|journal=Mycological Research|volume=113|issue=11|pages=1231–1241|doi=10.1016/j.mycres.2009.09.002|pmid=19747974 |issn=0953-7562|url-access=subscription}}</ref> Fungi from habitats with high concentration of salt are mostly halotolerant, few are halophilic.<ref name=":6" /> Halotolerant fungi constitute a relatively large and constant part of hypersaline environment communities, such as those in the solar salterns.<ref>{{Cite book | last1 = Zajc | first1 = J. | last2 = Zalar | first2 = P. | last3 = Plemenitaš | first3 = A. | last4 = Gunde-Cimerman | first4 = N. | doi = 10.1007/978-3-642-23342-5_7 | chapter = The Mycobiota of the Salterns | title = Biology of Marine Fungi | series = Progress in Molecular and Subcellular Biology | volume = 53 | pages = 133–158 | year = 2012 | isbn = 978-3-642-23341-8 | pmid = 22222830 }}</ref> Well studied examples include the yeast ''Debaryomyces hansenii ''and black yeasts ''Aureobasidium pullulans'' and ''Hortaea werneckii''which can grow in hyper saline conditions, making them model organisms to study halotolerance.<ref name=":7" /> The latter can grow in media without salt, as well as in almost saturated NaCl solutions. To emphasize this unusually wide adaptability, some authors describe ''H. werneckii ''as "extremely halotolerant".<ref>{{Cite book | last1 = Gostinčar | first1 = C. | last2 = Lenassi | first2 = M. | last3 = Gunde-Cimerman | first3 = N. | last4 = Plemenitaš | first4 = A. | title = Fungal Adaptation to Extremely High Salt Concentrations | doi = 10.1016/B978-0-12-387044-5.00003-0 | series = Advances in Applied Microbiology | volume = 77 | pages = 71–96 | year = 2011 | isbn = 978-0-12-387044-5 | pmid = 22050822 }}</ref>
Mechanisms of halotolerance in fungi include regulating intracellular ion concentrations and accumulating osmoprotectants to maintain osmotic balance without toxicity or disrupting cellular metabolic activity.<ref name=":7" />
== See also ==
* {{annotated link|Arabidopsis thaliana responses to salinity|''Arabidopsis thaliana'' responses to salinity}} * {{annotated link|Biosalinity}} * {{annotated link|Crop tolerance to seawater}} * {{annotated link|Salinity control}} * {{annotated link|Salt tolerance of crops}} * {{annotated link|Sodium in biology}} * {{annotated link|Soil salinity}} * {{annotated link|Soil salinity control}}
==References== {{reflist}}
{{Animalosmo}}
Category:Environmental microbiology Category:Geomicrobiology Category:Microbial growth and nutrition