Microbial Evolution Under Extreme Conditions by Bakermans Corien

Author:Bakermans, Corien [Bakermans, Corien]
Language: eng
Format: epub
Publisher: De Gruyter
Published: 2015-02-26T05:00:00+00:00

7.4 Phosphorus

Phosphorus (P) plays a central role in life, accounting for ∼ 3% of the dry weight of all organisms due to its presence in nucleic acids, ATP, phospholipids, and other biomolecules. The absence of an atmospheric reservoir of P makes it the ultimate limiting nutrient in many ecosystems. Its inorganic form, is the preferred source of phosphorus for microbial growth. Microbes likely evolved mechanisms to scavenge and store P early in Earth’s history [159]. One mechanism for P storage involves the intracellular production of P storage organelles, acidic calcium and P-rich membrane-bound structures called acidocalcisomes, in which P can be present as short- and long-chain polyphosphate (polyP), inorganic phosphate, or pyrophosphate [160],[161]. Under conditions of P limitation, diverse extremophiles are capable of acidocalcisome dissolution to use polyP for organic compound synthesis [162].

Around two-thirds of ocean surface waters are P-limited [163] and is particularly scarce (low nM) in subtropical gyres such as the Sargasso Sea in the north Atlantic [163]. Scavenging, storage, and substitution mechanisms for combatting P starvation are all utilized by marine microbes. Open ocean Prochlorococcus and Synechococcus possess numerous P transporters and utilize a wide variety of phosphate sources [154], [164][165] [166][167], in contrast to coastal strains that contain fewer P acquisition genes [153], [168]. Thus, as for nitrogen, there is an apparent evolutionary link between gene content for nutrient acquisition and survival in P-limited ecosystems. Moreover, in Prochlorococcus, most nutrient acquisition genes are found in genomic islands that are thought to have arisen by horizontal gene transfer and represent local and recent adaptation [154], [169]. Trichodesmium possesses alkaline phosphatases for stripping groups off of a variety of molecules [170], [171] and can also use organic P sources of phosphonate [172]. In the Sargasso Sea, cyanobacteria reduce cellular P demand by replacing phospholipids in their cellular membranes with nitrogen- and sulfur-containing lipids [173]. Using this mechanism, severely P-limited cyanobacteria are capable of lowering their P demands for lipid synthesis from ∼17 to 1%. Heterotrophic marine bacteria were not found to have this ability. This evolutionary capability may contribute to the dominance of cyanobacteria worldwide in oligotrophic marine regions [173]. However, heterotrophic marine bacteria of the SAR11 clade from the Sargasso Sea have alternative mechanisms for scavenging organic P, including the ability to acquire P from methylphosphonate, producing methane as a byproduct [174]. In contrast to the canonical view that polyP is only utilized as a luxury storage molecule, microbial polyP accumulation and rapid recycling was recently observed in the Sargasso Sea in parallel with other indicators of P stress, including alkaline phosphatase activity and substitution of sulfolipids for phospholipids [175],[176].

Terrestrial P-limited extremophilic communities have also evolved strategies for coping with P limitation. When placed under extreme P limitation, the thermophilic diazotrophic cyanobacterium Synechococcus strain OS- B’, isolated from microbial mats at Octopus Spring, Yellowstone National Park, can utilize organic phosphonates in place of inorganic P [177], [178]. In P-limited Lake Matano in Indonesia, betaine and glycolipids replace phospholipids [179].

While alternative lipids and sources of P can be

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