Water in Indian meteor crater changes colour over night.

The water in Lonar Lake, a flooded meteor crater in Maharashtra State, India, roughly 500 km to the east of Mumbai, turned from green to pink overnight this week, much to the surprise of local residents. The usually gets its colour from the Cyanobacterium Arthrospira spp., living in its upper layers, but apparently exceptionally warm weather in the area has caused both the temperature and the salinity of the lake to rise (the water level has gone down due to evaporation during the sustained warm spell, but the amount of salt in the lake has remained constant; the same amount of salt in a lower amount of water raises the salinity), until it eventually passed outside the tolerance level of Arthrospira spp., which died en masse. This enabled other organisms, notably the halophile (salt loving) Green Alga Dunaliella salina, which turns pink under stressful conditions, but has a higher environmental tolerance, to take over as the dominant group, blooming with the extra available resources; both an increased access to sunlight due to the the absence of Cyanobacteria, and nutrients released by the Cyanobacteria as they died.

Lake Lonar in pink (above) and green (below) colours. Deccan Herald/Twitter.

Conditions of high salinity are harmful to most organisms, due to the osmotic stress they induce. Put simply, the membranes of most micro-organisms are impervious to salt but allow water to pass through. Under most circumstances this is not a problem, but when the outside environment becomes too salty the water moves so that it is at the same concentration on either side of the membrane, flowing out of the organism and causing it to contract and die. Dunaliella salina is able to counteract this by producing glycerol and β-carotene in response to osmotic stress, which equalises the water concentration on either side of the cell membrane without changing the internal salinity, and incidentally turns it pink, and thus can take over as the dominant micro-organism when the salinity in a body of water exceeds the tolerance of other organisms.

 

Dunaliella salina cells in different culture conditions. (A) Green cell from a non-stressed culture. (B) Stressed cell turning orange. (C) Orange cell from a culture exposed to nutrient stress due to β-carotene accumulation. Scale bar represents 10 μm. Munevver Aksoy in Ramos et al. (2011).

Lake Lonar has an average diameter of 1.2 km, and sits within an impact crater with an average diameter of 1.8 km. It is slightly elliptical in shape, which has led to the estimation that it was formed by an object coming from the east, which struck at an angle of 35-40°. The crater was formerly thought to be about 50 000 years old, but recent estimates based upon argon-argon dating have suggested it may be as much as 570 000 years old.

Satellite image of Lonar Lake, showing the ejecta blanket surrounding it which identifies it as an impact crater. The smaller feature to the right is Lake Ambar, which is thought to have been caused by a fragment of the same object. Jesse Allen/Earth Observatory/NASA/Wikimedia Commons.

Argon-Argon dating relies on determining the ratio of radioactive Argon⁴⁰ to non-radioactive Argon³⁹ within minerals from igneous or metamorphic rock (in this case volcanic ash) to determine how long ago the mineral cooled sufficiently to crystallise. The ratio of Argon⁴⁰ to Argon³⁹ is constant in the atmosphere, and this ratio will be preserved in a mineral at the time of crystallisation. No further Argon³⁹ will enter the mineral from this point, but Argon⁴⁰ is produced by the decay of radioactive Potassium⁴⁰, and increases in the mineral at a steady rate, providing a clock which can be used to date the mineral.

 The approximate location of Lake Lonar. Google Maps,

The waters of Lake Lonar are both highly alkaline and highly saline, due to the chemistry of the rock on which it sits (basalt, from the Deccan Traps Flood Basalts) and the evaporitic nature of the lake; water does not flow out of Lake Loner, but is lost entirely by evaporation. The lake is fed by two small streams and the seasonal monsoon rains.

Monsoons are tropical sea breezes triggered by heating of the land during the warmer part of the year (summer). Both the land and sea are warmed by the Sun, but the land has a lower ability to absorb heat, radiating it back so that the air above landmasses becomes significantly warmer than that over the sea, causing the air above the land to rise and drawing in water from over the sea; since this has also been warmed it carries a high evaporated water content, and brings with it heavy rainfall. In the tropical dry season the situation is reversed, as the air over the land cools more rapidly with the seasons, leading to warmer air over the sea, and thus breezes moving from the shore to the sea (where air is rising more rapidly) and a drying of the climate.

Diagrammatic representation of wind and rainfall patterns in a tropical monsoon climate. Geosciences/University of Arizona.

The unique chemistry of Lonar Lake gives it a distinctive microbial community, typically dominated by Cyanobacteria, but with a broad range of Bacteria and Archaea, as well as Eukaryotic groups such as Alveolates, Fungi, Stramenopiles, Choanoflagellates, Amoebozoans and Cercozoans. Many of these Eukaryotic groups are thought to contain species endemic to the lake (i.e. not found elsewhere).

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Seven new species of Marine Fungi from the Mediterranean.

Marine Fungi are an important and active component of the microbial communities that inhabit the oceans. Fungi in the marine environment live as mutualists, parasites, pathogens and saprobes, and are pivotal to marine food webs because of the recycling of tough organic materials that other organisms cannot break down; besides which, these widely dispersed organisms are a source of novel bioactive compounds. Marine Fungi have been recovered worldwide from a broad range of biotic and abiotic substrata, such as driftwood algae, sponges, corals, sediments, etc. A 'Marine Fungus' is defined as any fungus retrieved repeatedly from marine environment and that reproduces in the marine environment. There are currently about 1680 described Marina Fungal species belonging to 693 genera, 223 families, 87 orders, 21 classes and six phyla. However, considering that the total number of Marine Fungi has been estimated to exceed 10 000 taxa, fungal diversity remains largely undescribed. With more than 900 species, the Ascomycota are the dominant Fungal phylum in the sea.

In a paper published in the journal Diversity on 6 April 2020, Anna Poli, Elena Bovio, Lucrezia Ranieri, Giovanna Cristina Varese, and and Valeria Prigione of the Department of Life Sciences and Systems Biology at the University of Torino describe seven ew species of Marine Ascomycote Fungi from the Mediterranean.

The first new species is placed in a new genus, Parathyridariella, which means 'beside Thyridariella', in reference to a previously described species, to which the new genus is closely related, and given the specific name dematiacea, meaning darkly pigmented, in reference to the colour of the colony on culture media  This species was isolated from a Green Seaweed, Flabellia petiolata, found growing at a depth of 14-15 m off the coast of Ghiaie Beach on the island of Elba, and a Seagrass, Posidonia oceanica, growing at a depth of 5-21 m off the coast of Punta Manara in the Province of Genoa, Italy. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 28–34 mm in diameter after 28 days at 24 °C, grown on Oatmeal Agar-sea water reached 40-34 mm in diameter after 28 days at 24°C, and on Potato Dextrose Agar-sea water reached 36-49 mm in diameter after 28 days at 24 °C, and 15.5–22.5 mm in diameter after 28 days at 15°C. The species grew actively on Pine wood and cork. The mycelium varies in colour from dark grey/black to dark green, and is dense with radial grooves and concentric rings, and submerged edges; the reverse is dark green. A brown exudate present above the concentric rings. The hyphae are 2.8–4.8 m wide, septate, hyaline to lightly pigmented. Parathyridariella dematiacea produces numerous Chlamydospores (thick-walled hyphal cells which function like spores), but neither sexual morphs or asexual conidiogenesis (spore production) were seen.

Parathyridariella dematiacea, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); solitary (C) and in chain (D) chlamydospores. Scale bars are 10 μ m (C), (D). Poli et al. (2020).

The second new species is also placed in the genus Parathyridariella, and given the specific name tyrrhenica, in reference to the Tyrrhenian Sea, where it was discovered. This species was isolated from a Brown Seaweed, Padina pavonica, (Peacock's Tail), and a Green Seaweed, Flabellia petiolata, both found growing at a depth of 14-15 m off the coast of Ghiaie Beach on the island of Elba. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 10 mm in diameter after 28 days, at 21° C, grown on Oatmeal Agar-sea water reached 48-50 mm in diameter after 28 days at 24°C, and 26-29 mm in diameter after 28 days at 15°C, and on Potato Dextrose Agar-sea water reached 31–46 mm in diameter after 28 days at 24 °C, and 16–19 mm in diameter after 28 days at 15°C. The species grew actively on Pine wood and cork. The mycelium is funiculose (made up of rope-like strands), yellowish, land ightly ochre at the edges; the reverse is light yellow, lighter at the edges. The hyphae are 5 μm diameter, septate, hyaline to brownish, sometimes wavy or swollen, forming hyphal strands. No reproductive structures were observed.

Parathyridaria tyrrhenica, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); mycelium (C), black and white arrows indicate hyphal strands and wavy hyphae, respectively. Scale bar is 10 μ m. Poli et al. (2020).

The third species described is also placed in the genus Parathyridaria, and given the specific name flabelliae, in reference to the Green Seaweed, Flabellia petiolata, on which it was found growing, at a depth of 14-15 m off the coast of Ghiaie Beach on the island of Elba. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 37–44 mm in diameter after 28 days, at 21° C, grown on Oatmeal Agar-sea water reached 60 mm in diameter after 28 days at 24°C, and 33–35 mm in diameter after 28 days at 15°C, and on Potato Dextrose Agar-sea water reached 53–64 mm in diameter after 28 days at 24 °C, and 23–24 mm in diameter after 28 days at 15°C. The species grew actively on Pine wood and cork. The mycelium is funiculose (made up of rope-like strands), and whitish with submerged edges; the reverse is brown in the middle, lighter at edges. The hyphae are 2.6-5 μ m wide, septate and hyaline. Parathyridariella flabelliae produces numerous Chlamydospores, which are globose or subglobose, from light to dark brown in colour, and either unicellular (4 x 5 μ m diameter) or multicellular (up to four-celled and 8 x 12 μm diameter), but neither sexual morphs or asexual conidiogenesis (spore production) were seen.

Parathyridaria flabelliae, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); unicellular and multicellular chlamydospores (C). Scale bar is 10 μm. Poli et al. (2020).

The fourth  new species described is placed in the genus Neoroussoella, and given the specific name lignicola, which implies it grows on dead wood.  This species was isolated from a Brown Seaweed, Padina pavonica, (Peacock's Tail), and a Seagrass, Posidonia oceanica, both found growing at a depth of 14-15 m off the coast of Ghiaie Beach on the island of Elba. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 28–29 mm in diameter after 28 days, at 21° C, grown on Oatmeal Agar-sea water reached 27-40 mm in diameter after 28 days at 24°C, and 14.5-26 mm in diameter after 28 days at 15°C, and on Potato Dextrose Agar-sea water reached 38–45 mm in diameter after 28 days at 24 °C, and 19–29 mm in diameter after 28 days at 15°C. This species grew efficiently on Pine wood. The mycelium is grey to dark green and floculose, with irregular edges, the reverse is dark grey. A clear exudate is often present. Hyphae are 2–4.4 m wide, septate, hyaline, and assume a toruloid aspect when growing into wood vessels; they form chains of two-celled chlamydospores which, at maturity, protrude from the vessels. The chlamydospores are 7.4 x 5.2 μ m, from light to dark brown, and globose or subglobose. Neither sexual morphs or asexual conidiogenesis (spore production) was seen.

Neoroussoella lignicola, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); two-celled chlamydospores inside wood vessels (C). Scale bar is 10 μm. Poli et al. (2020).

The fifth new species described is placed in the genus Roussoella, and given the specific namemargidorensis, meaning 'from Margidore'; the species was isolated from  a Brown Seaweed, Padina pavonica, (Peacock's Tail), found growing at a depth of 14-15 m off the coast of Margidore on the island of Elba. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 33-34 mm in diameter after 28 days, at 21° C, grown on Oatmeal Agar-sea water reached 45 mm in diameter after 28 days at 24°C, and 27 mm in diameter after 28 days at 15°C, and on Potato Dextrose Agar-sea water reached 45 mm in diameter after 28 days at 24 °C, and 23 mm in diameter after 28 days at 15°C. This species grew actively on Pine wood. The mycelium is whitish, lighter to the edge, and umbonate (having a rounded knob or protuberance) in the middle, the reverse is ochre. Hyphae are approximately 2 μm wide, septate and brownish. Neither sexual morphs or asexual conidiogenesis (spore production) was seen.

Roussoella margidorensis, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); chlamydospores (C). Scale bar is 10 μ m. Poli et al. (2020).

The sixth new species described is also placed in the genus Roussoella, and given the specific name mediterranea, in reference to the Mediterranean Sea. The species was isolated from  a Brown Seaweed, Padina pavonica, (Peacock's Tail), found growing at a depth of 14-15 m off the coast of Margidore on the island of Elba. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 55 mm in diameter after 28 days, at 21° C, grown on Oatmeal Agar-sea water reached 67–72 mm in diameter after 28 days at 24°C, and 33–38 mm in diameter after 28 days at 15°C, and on Potato Dextrose Agar-sea water reached 69–76 mm in diameter after 28 days at 24 °C, and 32.5–39 mm in diameter after 28 days at 15°C. This species grew actively on Pine wood, and poorly on cork. The mycelium is light grey, and floccose, with an umbonate area in the middle, the reverse is brown with lighter edges. A dark exudate present. Hyphae are 2.4 μm wide, septate and dematiaceous. Branched chains of light to dark brown chlamydospores often present, these are 4.5 x 5.7 μm, and from unicellular to 4-celled. Neither sexual morphs or asexual conidiogenesis (spore production) was seen.

Roussoella mediterranea, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); unicellular and multicellular chlamydosporesn indicated by a black arrow (C). Scale bar is 10 μ m. Poli et al. (2020).

The final species is also placed in the genus Roussoella, and given the specific name padinae, in reference to the Brown Seaweed, Padina pavonica, (Peacock's Tail), upon which it was found growing, at a depth of 14-15 m off the coast of Margidore on the island of Elba. Colonies of this Fungus grown on Malt Extract Agar-sea water media reached 53 mm in diameter after 28 days, at 21° C, grown on Oatmeal Agar-sea water reached 57.5–65 mm in diameter after 28 days at 24°C, and 30–35 mm in diameter after 28 days at 15°C, and on Potato Dextrose Agar-sea water reached 60–69 mm in diameter after 28 days at 24 °C, and 30–34 mm in diameter after 28 days at 15°C. This species grew poorly on Pine wood, and efficiantly on cork. The mycelium is from grey to dark green, floccose in the middle, with radial grooves, and fimbriate edges; the reverse is brown. Hyphae are 3 μm wide, septate, brownish and assume a toluroid aspect when growing into wood vessels, and form chains of two-celled chlamydospores which, at maturity, protrude from the vessels. These chlamydospores are 5–7 x 4 μm, from light to dark brown in colour, subglobose, ellipsoidal or cylindrical. Neither sexual morphs or asexual conidiogenesis (spore production) was seen.

 Roussoella padinae, 28-days-old colony at 21°C on Malt Extract Agar-sea water media (A) and reverse (B); toruloid hyphae (C) and two-celled chlamydospores (D) inside wood vessels. Scale bars are 10 μm. Poli et al. (2020).

The description of these new taxa was particularly challenging because neither asexual nor sexual reproductive structures developed in axenic conditions. Therefore, Poli et al. were unable to describe the range of anatomical variations and diagnostic features among these newly recognized phylogenetic lineages. Indeed, strictly vegetative growth without sporulation is a common feature of many marine Fungal strains. Possibly, these organisms rely on hyphal fragmentation for their dispersal, or alternatively, the di erentiation of reproductive structures may be obligatorily dependent on the peculiar environmental conditions under which they live (e.g., wet-dry cycles, high salinity, low temperature, high pressure, etc.). During the study of these fungi, Poli et al. tried to mimic the saline environment by using di erent culture media supplemented with natural sea water or sea salts. Although these culture methods were applied to induce sporulation, they observed that only media supplemented with sea water supported a measurable growth of vegetative mycelium. A method tried previously with other Marine Fungi, to induce sporulation by placing wood and cork specimens on the colony surface with their subsequent transfer into sea water, was only partially successful: out of seven species, three (Parathyridariella dematiacea, Parathyridariella flabelliae, Roussoella mediterranea) developed chlamydospores in the mycelium above the wood surface, two (Neoroussoella lignicola, Roussoella padinae) gave rise to resting spores inside wood vessels. Most of the strains preferred to colonise wood rather than cork. These structures were interpreted as 'chlamydospores' instead of 'conidia' for the following reasons: (i) They were characterized by a very thick cell wall, a typical feature of resting spores; (ii) conidiogenous cells were never observed. Additional e orts to force the development of reproductive structures by using Syntetic Nutrient Agar-sea water and Pine needles, were also unsuccessful.

Both Roussoella padinae and Neoroussoella lignicola displayed a similar lignicolous behavior, growing and producing chlamydospores inside wooden vessels, although of di erent size and shape. The ability to form hyphae and to grow inside the wood vessels has been reported for a number of dark septate endophyte Fungi in terrestrial environments, and, recently, for Posidoniomyces atricolor, marine endophyte that lives in association with the roots of the Seagrass, Posidonia oceanica. By definition, endophytes live inside living plant tissues. To induce sporulation, sterilized specimens of dead wood were employed, therefore Roussoella padinae and Neoroussoella lignicola were inferred to be 'lignicolous Fungi' rather than 'endophytes'. The observation of this growth characteristic in two di erent genera, may find its reason in an evolutionary adaptation to marine life in association with lignocellulosic matrices. Therefore, Poli et al. hypothesise their ecological role as saprobes involved in degrading organic matter.

Most of the Roussoellaceae (the family that includes the genera Roussoella and Neoroussoella) and Thyridariaceae (the family that includes the genus Parathyridariella) described to date are associated with terrestrial plants, especially Bamboo and Palm species. In fact, only two species, Roussoella mangrovei and Roussoella nitidula have previously been retrieved from the marine environment. However, Poli et al. infer that these families may be well represented in the sea, thus improving our knowledge on the largely unexplored Fungal marine biodiversity.

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