**3. Haloarchaea**

Archaea, one of the three Domains of life, make up a significant fraction of the microbial biomass on Earth [47]. It was thought that Archaea microbes were restricted to extreme environments, such as those with elevated temperatures, low or high pH, high salinity, or strict anoxia [48]. However, environmental sampling analysis based on rRNA sequences has revealed that archaea are widespread in "normal" ecosystems, including soils, oceans, marshlands, human colon, human oral cavity and even in human skin. They are particularly numerous in the oceans; thus, archaea in plankton may constitute one of the most abundant groups of organisms on the planet. From a metabolic point of view, they have evolved a variety of energy metabolisms using organic and/or inorganic electron donors and acceptors, playing important roles in the Earth's global geochemical cycles [49].

Salty environments are dominated by organisms commonly named "halophiles" (it comes from the Greek word for "salt-loving"). They are usually classified into three groups according to their NaCl requirements: slight halophiles (2–5% or 0.34–0.85 M), moderate halophiles (5–20% or 0.85–3.4 M) and extreme halophiles (20–30% or 3.4–5.1 M) [50].

Halophilic archaea, also called Haloarchaea, are extreme or moderated halophilic species inhabiting neutral saline environments such as salt lakes, marine salterns, marshes, saltern crystallizer ponds or genuine environments like the Dead Sea [51, 52]. In those natural ecosystems, salt concentrations are around 1.5–4 M, which corresponds to 9–30% of salts (w/v). NaCl is the predominant salt and ionic proportions are like those dissolved salts in seawater.

These halophilic ecosystems harbour a large diversity of microorganisms of all three domains: small eukaryotes such the shrimp *Artemia salina*, primary producers as the green algae *Dunaliell*a [14] (**Figure 2A** and **B**), aerobic heterotrophic bacteria (mainly belonging to the family *Halomonadaceae*), anaerobic fermentative bacteria (families *Halanaerobiaceae* and *Halobacteroidaceae*) and archaeal microorganisms of the families *Halobacteriaceae* and *Haloferacaceae* (commonly named "Haloarchaea"). They are mainly characterised by their red-orange-pink colour, which is due to the pigments they produce to be protected against the high sun radiation (**Figure 3**). Salted ponds for salt crystallisation or other salty ecosystems like de Dead Sea become completely red, mainly in summer, due to microbial blooms, in which haloarchaea of the genera *Haloarcula*, *Haloferax*, *Haloquadratu*m or bacterial species like *Salinibacter ruber* constitute de major populations (**Figures 2C** and **3**).

**29**

**marine birds**

**Figure 2.**

**Figure 3.**

*the world.*

*Haloarchaea May Contribute to the Colour of Avian Plumage in Marine Ecosystems*

**4. Haloarchaea and their relation to avian plumage colour: the case of** 

*(A)* Haloferax volcanii *colonies; (B)* Haloquadratum walsbii *cells (picture from https://microbewiki.kenyon. edu/index.php/Haloquadra) and (C)* Haloferax mediterranei *colonies. Flamingos display haloarchaeal colours, they often frequent hypersaline lakes, and they carry haloarchaea with them on their travels around* 

*(A)* Artemia salina *and (B)* Dunaliella salina*. They constitute the major microbial populations in salted waters in coastal environments, salted lagoons, salty ponds from where NaCl is isolated from human consumption, etc. (C) Aerial overview of the saltern ponds located in Santa Pola city (Southeast of Spain) (http://paisajesturisticosvalencianos.com/paisajes/las-salinas-de-santa-pola-torrevieja/). This kind of ecosystems are warm places frequently inhabited by seaside birds like flamingos (D). The colour of the ponds is* 

Studies in the early nineties of the last century demonstrated that the carotenoids of the feathers were derived from the diet and deposited within tissues selectively [53] being the liver one of the most important organs involved in the conversion of carotenoids uptaken [54]. Some years before, other studies focused on seaside birds as flamingos stated that the major carotenoids in blood and feathers were canthaxanthin and a rare β-carotene derivative (4-keto-α-carotene) [55, 56]. Limitations on

*DOI: http://dx.doi.org/10.5772/intechopen.96414*

*due to microbial blooms, which occur mainly in summer.*

*Haloarchaea May Contribute to the Colour of Avian Plumage in Marine Ecosystems DOI: http://dx.doi.org/10.5772/intechopen.96414*

#### **Figure 2.**

*Birds - Challenges and Opportunities for Business, Conservation and Research*

red pigment also found almost exclusively in turacos [39].

**3. Haloarchaea**

cycles [49].

(20–30% or 3.4–5.1 M) [50].

proportions are like those dissolved salts in seawater.

*ruber* constitute de major populations (**Figures 2C** and **3**).

carotenoids [28, 42]. On the one hand, melanin-based coloration switches from brown to black due to the presence of phaeomelanin or eumelanin, respectively, or the number and distribution of the melanosomes [29, 30]. On the other hand, carotenoids-based colorations vary from yellow to red as previously mentioned. The genetics of coloration in birds remains poorly described. However, it is extensively accepted that its expression is phenotypically plastic with a high sensitivity to variation in environmental conditions. Therefore, the melanin-based colour should be considered the key system to understand the molecular basis of phenotypic variations [43]. Some other pigments are only present in some species. This is the case of psittacofulvins, which are found just in a few species of parrots (*Psittacidae*) or penguins (*Spheniscidae*) [44–46] or turacoverdins, responsible for the bright green coloration of several birds of the family *Musophagidae*, most notably the turaco (*Turac*o sp.; *Musophagidae*). It is chemically related to turacin, a

Archaea, one of the three Domains of life, make up a significant fraction of the microbial biomass on Earth [47]. It was thought that Archaea microbes were restricted to extreme environments, such as those with elevated temperatures, low or high pH, high salinity, or strict anoxia [48]. However, environmental sampling analysis based on rRNA sequences has revealed that archaea are widespread in "normal" ecosystems, including soils, oceans, marshlands, human colon, human oral cavity and even in human skin. They are particularly numerous in the oceans; thus, archaea in plankton may constitute one of the most abundant groups of organisms on the planet. From a metabolic point of view, they have evolved a variety of energy metabolisms using organic and/or inorganic electron donors and acceptors, playing important roles in the Earth's global geochemical

Salty environments are dominated by organisms commonly named "halophiles" (it comes from the Greek word for "salt-loving"). They are usually classified into three groups according to their NaCl requirements: slight halophiles (2–5% or 0.34–0.85 M), moderate halophiles (5–20% or 0.85–3.4 M) and extreme halophiles

Halophilic archaea, also called Haloarchaea, are extreme or moderated halophilic species inhabiting neutral saline environments such as salt lakes, marine salterns, marshes, saltern crystallizer ponds or genuine environments like the Dead Sea [51, 52]. In those natural ecosystems, salt concentrations are around 1.5–4 M, which corresponds to 9–30% of salts (w/v). NaCl is the predominant salt and ionic

These halophilic ecosystems harbour a large diversity of microorganisms of all three domains: small eukaryotes such the shrimp *Artemia salina*, primary producers as the green algae *Dunaliell*a [14] (**Figure 2A** and **B**), aerobic heterotrophic bacteria (mainly belonging to the family *Halomonadaceae*), anaerobic fermentative bacteria (families *Halanaerobiaceae* and *Halobacteroidaceae*) and archaeal microorganisms of the families *Halobacteriaceae* and *Haloferacaceae* (commonly named "Haloarchaea"). They are mainly characterised by their red-orange-pink colour, which is due to the pigments they produce to be protected against the high sun radiation (**Figure 3**). Salted ponds for salt crystallisation or other salty ecosystems like de Dead Sea become completely red, mainly in summer, due to microbial blooms, in which haloarchaea of the genera *Haloarcula*, *Haloferax*, *Haloquadratu*m or bacterial species like *Salinibacter* 

**28**

*(A)* Artemia salina *and (B)* Dunaliella salina*. They constitute the major microbial populations in salted waters in coastal environments, salted lagoons, salty ponds from where NaCl is isolated from human consumption, etc. (C) Aerial overview of the saltern ponds located in Santa Pola city (Southeast of Spain) (http://paisajesturisticosvalencianos.com/paisajes/las-salinas-de-santa-pola-torrevieja/). This kind of ecosystems are warm places frequently inhabited by seaside birds like flamingos (D). The colour of the ponds is due to microbial blooms, which occur mainly in summer.*

#### **Figure 3.**

*(A)* Haloferax volcanii *colonies; (B)* Haloquadratum walsbii *cells (picture from https://microbewiki.kenyon. edu/index.php/Haloquadra) and (C)* Haloferax mediterranei *colonies. Flamingos display haloarchaeal colours, they often frequent hypersaline lakes, and they carry haloarchaea with them on their travels around the world.*
