Biological soil crusts and how they might colonize other worlds: insights from these Brazilian ecosystem engineers

Glutamate dehydrogenase in "Liverworld"-A study in selected species to explore a key enzyme of plant primary metabolism in Marchantiophyta

In plants, glutamate dehydrogenase (GDH) is an ubiquitous enzyme that catalyzes the reversible amination of 2-oxoglutarate in glutamate. It contributes to both the amino acid homeostasis and the management of intracellular ammonium, and it is regarded as a key player at the junction of carbon and nitrogen assimilation pathways. To date, information about the GDH of terrestrial plants refers to a very few species only. We focused on selected species belonging to the division Marchantiophyta, providing the first panoramic overview of biochemical and functional features of GDH in liverworts. Native electrophoretic analyses showed an isoenzymatic profile less complex than what was reported for Arabidposis thaliana and other angiosperms: the presence of a single isoform corresponding to an α-homohexamer, differently prone to thermal inactivation on a species- and organ-basis, was found. Sequence analysis conducted on amino acid sequences confirmed a high similarity of GDH in modern liverworts with the GDH2 protein of A. thaliana, strengthening the hypothesis that the duplication event that gave origin to GDH1-homolog gene from GDH2 occurred after the evolutionary bifurcation that separated bryophytes and tracheophytes. Experiments conducted on Marchantia polymorpha and Calypogeia fissa grown in vitro and compared to A. thaliana demonstrated through in gel activity detection and monodimensional Western Blot that the aminating activity of GDH resulted in strongly enhanced responses to ammonium excess in liverworts as well, even if at a different extent compared to Arabidopsis and other vascular species. The comparative analysis by bi-dimensional Western Blot suggested that the regulation of the enzyme could be, at least partially, untied from the protein post-translational pattern. Finally, immuno-electron microscopy revealed that the GDH enzyme localizes at the subcellular level in both mitochondria and chloroplasts of parenchyma and is specifically associated to the endomembrane system in liverworts.

Seasonal variation in soil algal community structure in different forest plantations in subtropic China

Algae exert great impact on soil formation and biogeochemical cycling. However, there is no full understanding of the response of soil algal community structure to the seasonal fluctuations in temperature and moisture and changes of soil physicochemical properties across different forests. Here, based on 23S rRNA gene sequencing, we analyzed soil algal community structure in four different forest plantations in two seasons and examined soil physiochemical properties. The results showed the significantly seasonal variation in soil algal community structure, with the higher overall diversity in summer than in winter. In addition, there existed significant correlations between soil algae (species composition, relative abundance, diversity index) and physicochemical properties (pH, total phosphorus, organic matter and nitrate nitrogen), suggesting that edaphic characteristics are also largely responsible for the variation in soil algal community. Nevertheless, the seasonal variation in algal community structure was greater than the variation across different forest plantations. This suggest temperature and moisture are more important than soil physicochemical properties in determining soil algal community structure. The findings of the present study enhance our understanding of the algal communities in forest ecosystems and are of great significance for the management and protection of algal ecosystem.

Photoautotrophic black-colored cyanobacterial soil crust biosynthesizes photoprotective compounds and is capable of using blue, green, and red wavelengths of light for its growth

Several cyanobacteria can adjust their light-harvesting machinery in response to existing light signals in a process called chromatic acclimation (CA) which permits the utilization of available light resources for photosynthesis. CA involves alteration in the pigment composition of a major light-harvesting complex called phycobilisome (PBS) and allows some cyanobacteria to utilize green light (GL) to drive photosynthesis. However, cyanobacteria, in contrast with eukaryotic algae and higher plants, can not utilize blue light (BL) for photosynthesis due to their dependency on PBS. Here, we studied a black-colored soil crust that was composed of a single cyanobacterium identified and named Oscillatoria sp. Malviya-1 after phenotypic and phylogenetic analyses. The black-colored crust can absorb light from almost all parts of photosynthetically active radiation (400-700 nm) and ultraviolet radiation (280-400 nm) due to the presence of photosynthetic pigments and microbial sunscreens such as chlorophyll ɑ, carotenoids, phycoerythrin, phycocyanin, allophycocyanin, mycosporine-like amino acids, and scytonemin. Unlike other cyanobacteria, Oscillatoria sp. Malviya-1 can grow using GL, BL, and red light (RL) in addition to white light (WL) which was accompanied by the different colors of the mat under different light conditions. The presence of CA and sunscreens compounds can maximize the fitness of soil crust under a dynamic light environment, UVR, and desiccation. Detailed study of Oscillatoria sp. Malviya-1 will provide information on the mechanism of CA in cyanobacterial soil crust and its unique ability to use both GL and BL.