Evolution of acidocalcisomes and their role in polyphosphate storage and osmoregulation in eukaryotic microbes

Abstract

Acidocalcisomes are acidic electron-dense organelles, rich in polyphosphate (poly P) complexed with calcium and other cations. While its matrix contains enzymes related to poly P metabolism, the membrane of the acidocalcisomes has a number of pumps (Ca 2+ -ATPase, V-H + -ATPase, H + -PPase), exchangers (Na + /H + , Ca 2+ /H + ), and at least one channel (aquaporin). Acidocalcisomes are present in both prokaryotes and eukaryotes and are an important storage of cations and phosphorus. They also play an important role in osmoregulation and interact with the contractile vacuole complex in a number of eukaryotic microbes. Acidocalcisomes resemble lysosome-related organelles (LRO) from mammalian cells in many of their properties. They share similar morphological characteristics, acidic properties, phosphorus contents and a system for targeting of their membrane proteins through adaptor complex-3 (AP-3). Storage of phosphate and cations may represent the ancestral physiological function of acidocalcisomes, with cation and pH homeostasis and osmoregulatory functions derived following the divergence of prokaryotes and eukaryotes.

Microbial biomass, nutrient availability and nutrient uptake by wheat in two soils with organic amendments

“…On the other hand, microbial P uptake can prevent P fixation by soil colloids (Ayaga et al, 2006;Gichangi et al, 2009;Khan and Joergensen, 2009) or leaching of N. Microbial biomass N and P become availableto plants upon microbial turnover when the easily available C is depleted (Gichangi et al, 2009;Malik et al, 2012). Thus microbes can be considered as slow release fertilisers that store nutrients (mainly N and P) when nutrient concentrations are high and then release them (Ryazanova et al, 2009;Docampo et al, 2010).…”

Importance of Radioactive Labelling to Elucidate Inositol Polyphosphate Signalling

“…One such use was the original identification of inositol pyrophosphates in D. discoideum extracts [3]: the saxHPLC elution region for these high-polarity molecules in this organism is conveniently free from interference from contaminating phosphorylated molecules. This is not the case for extracts from cell types rich in the linear polymer of phosphates [62,63] inorganic polyphosphate (polyP), such as yeast or trypanosomes, where polyP is particularly abundant [64][65][66]. In these organisms, orthophosphate labelling experiments will reveal the continuous presence throughout the chromatogram of radiolabelled polyP peaks that cover the InsP 6 , InsP 7 and InsP 8 signals (A. Saiardi, unpublished observation).…”

Inseparable tandem: evolution chooses ATP and Ca2+to control life, death and cellular signalling

“…ADP system can be explained by the requirement of only one energy limiting step for ATP re-synthesis, rather than two for the pyrophosphatase system, whereas the same amount of free energy is available for both [80]. Thus, pyrophosphatase-driven Ca 2þ -sequestration is used only exceptionally, for example in acidocalcisomes of trypanosome parasites [81].…”