Amazon Forest Is Located In Which Continent | loss of biodiversity in the (amazon rainforest)

16.3.1.1 Amazon Rainforest

The Amazon Rainforest is globally recognized as one of the greatest and richest tropical forests in terms of area and biodiversity (Malhi et al., 2008). It is also known as a myriad of streams and rivers converging to form the Amazon River, the largest river in the world in terms of water discharge (Gibbs, 1972). It covers almost 25% of South America and it extends into nine countries with about 7.5 million km2, with more than 70% of tropical rainforest species and one-third of the world´s germplasm being restricted to this biome. It is considered one of the last continuous extensions of humid tropical forests of Earth (Fearnside, 2005; Cenciani et al., 2011). In general, the climate is characterized by warm temperatures (ranging from 24 to 27°C all year), high rainfall (around 3200 mm/year) and high relative humidity (from 80% to 94%, throughout the year), being classified as a humid and semihot equatorial biome (FAO, 2015).

The most conspicuous differentiating factor in this biome is the diversity of landscapes modulated by the availability of water, being categorized as dryland forest, swamp and seasonal-swamp forests along the watercourses on the flood plains (Bass et al., 2010; FAO, 2015). This variation on water availability contributes to the emergence of extreme environments and the identification of these zones may reveal hitherto unnoticed aspects of evolutionary processes. Some Amazonian areas have shown soils with high concentration of aluminum (145 mmol/kg), ferrous iron, low chemical fertility and unfavorable physical properties. Those metallic reduced forms become available in the soil as the pH drops below 5, turning them into acidic environments with predominance of podzolic and acrisol soil types, respectively (FAO, 2009). These soils occur mostly along the Negro River (Rio Negro) and the northern upper Amazon Basin, surrounding the microregion of Barcelos (mesoregion of Rio Negro, Amazônia state—AM) and Tapauá (microregion of Caracaraí, Rondônia state—RO) (Diaz-Castro et al., 2003; FAO, 2015).

Other important factors are the astonishingly high levels of UV radiation and high temperatures that microorganisms colonizing the leaf surfaces of plants have to face (Morton et al., 2016; Saleska et al., 2016). The region of Conceição do Araguaia municipality, in the west side of Pará state (S8°15′29″, W49°16′11″), was recorded with the highest levels of UV radiation in Brazil, with extreme values of ca. 6.5 kW h/m2, coupled with low precipitation between June and August (below 20 mm) (Saleska et al., 2016). Additional elements to be considered are exacerbated rate of deforestation (increased by 29%, FAO, 2015), combined with the progression of fire seasons (1244 fire events were alerted just in January, Global Forest Watch, 2018). These factors have contributed to the emergence of areas under the process of desertification, occurring around the cities of Rio Branco (the capital of Acre state—AC), Rondônia state (RO), Pará state (PA) and Mato Grosso state (MT) (Barber et al., 2014; Global Forest Watch, 2018).

The biodiversity is mainly thought of in terms of animals and plants, but the environmental conditions, such as high temperatures, humidity, solar radiation and precipitation, allow the microbiological diversity to flourish. Among them, the phylum Cyanobacteria is notable given its nutritional simplicity and phototrophic metabolism, as well as the possible existence of physiological and morphological mechanisms allowing them to couple with the high solar radiation of Equator over the year. However, studies exploring the diversity of cyanobacteria in the Amazon Rainforest are scarce and most of them were conducted based only on microscopic observations of environmental samples, resulting in pictures, drawings and lists of observed species/morphotypes from specific sites (Vieira et al., 2003, 2005; Aboim et al., 2016). Considering studies dealing with isolation and cultivation, it has been shown that some Amazonian rivers support considerable diversity of homocytous cyanobacteria (Genuário et al., 2017b), with the possibility of discovering new species (Fiore et al., 2005; Genuário et al., 2018). Areas under high UV incidence could potentially be exploited for new cyanobacterial species able to produce pigment molecules like scytonemin that can be used in photoprotection and biomedical research (Rastogi et al., 2015).

The polyphasic approach has been applied for the characterization of isolated cyanobacterial strains in few studies (Fiore et al., 2005; Genuário et al., 2017b, 2018), while culture-independent methodologies have been even less used (Dall’agnol et al., 2012; Pureza et al., 2013). The polyphasic approach was firstly oriented toward the examination of filamentous heterocytous nitrogen-fixing cyanobacterial strains (Fiore et al., 2005) and only lately, the filamentous homocytous forms were also investigated (Genuário et al., 2017b). Likewise, some cyanobacterial strains isolated from several Amazonian habitats have had their whole genome sequenced such as Cyanobium (Lima et al., 2014), Synechococcus (Guimarães et al., 2015), Nostoc (Leão et al., 2016) and Microcystis (Castro et al., 2016). However, these cultured cyanobacteria and the genetic information retrieved from their genomes were not further investigated in vitro neither in silico, which could have uncovered the mechanisms involved in the adaptation of this group of microorganisms to high solar radiation and other extreme conditions.

Among the studies in which cyanobacterial strains were sampled, heterocytous strains were isolated from 14 locations along the mainstream of Solimões and Amazon rivers (Fiore et al., 2005). These strains were morphologically identified as belonging to the genera Nostoc, Cylindrospermum and Fischerella (Fiore et al., 2005). However, considering the 16S rRNA gene phylogeny, these morphotypes did not correspond to the typical phylogenetic lineage of their respective genus, indicating the emergence of new phylogenetic lineages reassembling well-known morphotypes (Fiore et al., 2005). On the other hand, the homocytous strains recently identified by morphology as belonging to the genera Pseudanabaena, Leptolyngbya, Planktothrix and Phormidium had their 16S rRNA sequences clustered with strong support into the typical phylogenetic clusters of the abovementioned genera, showing a more robust congruence between morphological and molecular data (Genuário et al., 2017b). Despite this, in the same study, some strains morphologically identified as members of the genera Leptolyngbya and Phormidium were, indeed, related to the phylogenetic clusters of the recently described genera Pantanalinema, Alkalinema and Cephalothrix, respectively (Genuário et al., 2017b). These results demonstrated that Amazonas and Solimões rivers hold a cultured diversity of cyanobacteria similar to those already recorded from other aquatic environments around the world or in Brazil (Genuário et al., 2017b).

In addition, one novel cyanobacterial strain isolated from Solimões river (Rio Solimões) was recently described based on a polyphasic approach as a new species, Cronbergia amazonensis (Genuário et al., 2018). In addition to the description of this new species, this work also highlighted the existence of three 16S rRNA gene sequences named Cronbergia siamensis SAG 11.82 (type-species and reference sequence for the genus Cronbergia), which fall into two distinct phylogenetic lineages (1) one clustered with the typical Cylindrospermum cluster and (2) another grouped with the novel Amazonian sequence. In conclusion, this investigation has supported the genus Cronbergia as a valid and stable cyanobacterial genus and provided great insights in the Cronbergia dilemma (Genuário et al., 2018) (Figs. 16.3–16.5).

Figure 16.3. Maximum likelihood phylogenetic tree based on the 16S rRNA gene sequences of Unicellular cyanobacterial strains. The 16S rRNA gene sequences retrieved from GenBank were aligned using CLUSTAL W from MEGA version 5 and trimmed (16S rRNA gene matrix with a 1447-bp length). A total of 159 sequences were considered and used to infer the phylogeny based on the ML method. The general time reversible evolutionary model of substitution with gamma distribution and with an estimate of proportion of invariable sites (GTR+G+I) was selected as the best fitting model, applying the model-testing function in MEGA version 5. The robustness of the phylogenetic tree was estimated by bootstrap analysis using 1000 replications. ML, maximum likelihood.

Figure 16.4. Maximum likelihood phylogenetic tree based on the 16S rRNA gene sequences of filamentous non-heterocytous cyanobacterial strains. The 16S rRNA gene sequences retrieved from GenBank were aligned using CLUSTAL W from MEGA version 5 and trimmed (16S rRNA gene matrix with a 1452-bp length). A total of 138 sequences were considered and used to infer the phylogeny based on the ML method. The general time reversible evolutionary model of substitution with gamma distribution and with an estimate of proportion of invariable sites (GTR+G+I) was selected as the best fitting model, applying the model-testing function in MEGA version 5. The robustness of the phylogenetic tree was estimated by bootstrap analysis using 1000 replications. ML, maximum likelihood.

Figure 16.5. NJ phylogenetic tree based on the 16S rRNA gene sequences of Filamentous heterocytous cyanobacterial strains. The 16S rRNA gene sequences retrieved from GenBank were aligned using CLUSTAL W from MEGA version 5 and trimmed (16S rRNA gene matrix with a 1452-bp length). A total of 175 sequences were considered and used to infer the phylogeny based on the NJ method. The Kimura 2-parameter model of substitution with gamma distribution and with an estimate of proportion of invariable sites (K2+G+I) was selected as the best fitting model, applying the model-testing function in MEGA version 5. The robustness of the phylogenetic tree was estimated by bootstrap analysis using 1000 replications. NJ, neighbor-joining.