Desert Biological Soil Crusts Research Articles

Genomic imprints of unparalleled growth.

Chlorella ohadii was isolated from desert biological soil crusts, one of the harshest habitats on Earth, and is emerging as an exciting new green model for studying growth, photosynthesis and metabolism under a wide range of conditions. Here, we compared the genome of C. ohadii, the fastest growing alga on record, to that of other green algae, to reveal the genomic imprints empowering its unparalleled growth rate and resistance to various stressors, including extreme illumination. This included the genome of its close relative, but slower growing and photodamage sensitive, C. sorokiniana UTEX 1663. A larger number of ribosome-encoding genes, high intron abundance, increased codon bias and unique genes potentially involved in metabolic flexibility and resistance to photodamage are all consistent with the faster growth of C. ohadii. Some of these characteristics highlight general trends in Chlorophyta and Chlorella spp. evolution, and others open new broad avenues for mechanistic exploration of their relationship with growth. This work entails a unique case study for the genomic adaptations and costs of exceptionally fast growth and sheds light on the genomic signatures of fast growth in photosynthetic cells. It also provides an important resource for future studies leveraging the unique properties of C. ohadii for photosynthesis and stress response research alongside their utilization for synthetic biology and biotechnology aims.

Mass spectrometry and spectroscopic characterization of a tetrameric photosystem I supercomplex from Leptolyngbya ohadii, a desiccation-tolerant cyanobacterium

Cyanobacteria inhabiting desert biological soil crusts face the harsh conditions of the desert. They evolved a suite of strategies toward desiccation-hydration cycles mixed with high light irradiations, etc. In this study we purified and characterized the structure and function of Photosystem I (PSI) from Leptolyngbya ohadii, a desiccation-tolerant desert cyanobacterium. We discovered that PSI forms tetrameric (PSI-Tet) aggregate. We investigated it by using sucrose density gradient centrifugation, clear native PAGE, high performance liquid chromatography, mass spectrometry (MS), time-resolved fluorescence (TRF) and time-resolved transient absorption (TA) spectroscopy. MS analysis identified the presence of two PsaB and two PsaL proteins in PSI-Tet and uniquely revealed that PsaLs are N-terminally acetylated in contrast to non-modified PsaL in the trimeric PSI from Synechocystis sp. PCC 6803. Chlorophyll (Chl) a fluorescence decay profiles of the PSI-Tet performed at 77 K revealed two emission bands at ∼690 nm and 725 nm with the former appearing only at early delay time. The main fluorescence emission peak, associated with emission from the low energy Chls a, decays within a few nanoseconds. TA studies demonstrated that the 725 nm emission band is associated with low energy Chls a with absorption band clearly resolved at ∼710 nm at 77 K. In summary, our work suggests that the heterogenous composition of PsaBs and PsaL in PSI-Tet is related with the adaptation mechanisms needed to cope with stressful conditions under which this bacterium naturally grows.

Geminicoccus flavidas sp. nov. and Geminicoccus harenae sp. nov., two IAA-producing novel rare bacterial species inhabiting desert biological soil crusts.

Two Gram-staining negative strains (CPCC 101082T and CPCC 101083T) were isolated from biological sandy soil crusts samples collected from Badain Jaran desert, China. Both isolates were heterotrophic phototroph, could produce indole-3-acetic acid. The 16S rRNA gene sequences of these two strains were closely related to the members of the family Geminicoccaceae, showing high similarities with Geminicoccus roseus DSM 18922T (96.9%) and Arboricoccus pini B29T1T (90.1%), respectively. In phylogenetic tree based on 16S rRNA gene sequences, strain CPCC 101082T and CPCC 101083T formed a robust distinct clade with Geminicoccus roseus DSM 18922T within the family Geminicoccaceae, which indicated that these two isolates could be classified into the genus Geminicoccus. The growth of strain CPCC 101082T occurred at 15-42°C and pH 4.0-10.0 (optima at 28-37°C and pH 6.0-8.0). The growth of strain CPCC 101083T occurred at 4-45°C and pH 4.0-10.0 (optima at 25-30°C and pH 6.0-8.0). The major cellular fatty acids of CPCC 101082T and CPCC 101083T contained C18:1 ω7c/C18:1 ω6c, cyclo-C19:0 ω8c, and C16:0. Q-10 was detected as the sole respiratory quinone. Diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, phosphatidylethanolamine, an unidentified phospholipid and an unidentified aminolipid were tested in the polar lipids profile. The genomes of the two isolates were characterized as about 5.9 Mbp in size with the G + C content of nearly 68%. The IAA-producing encoding genes were predicated in both genomes. The values of average nucleotide identity were 80.6, 81.2 and 92.4% based on a pairwise comparison of the genomes of strains CPCC 101082T and CPCC 101083T and Geminicoccus roseus DSM 18922T, respectively. On the basis of the genotypic, chemotaxonomic and phenotypic characteristics, the strains CPCC 101082T (=NBRC 113513T = KCTC 62853T) and CPCC 101083T (=NBRC 113514T = KCTC 62854T) are proposed to represent two novel species of the genus Geminicoccus with the names Geminicoccus flavidas sp. nov. and Geminicoccus harenae sp. nov.

Divergence of Biocrust Active Bacterial Communities in the Negev Desert During a Hydration-Desiccation Cycle.

Rain events in arid environments are highly unpredictable and intersperse extended periods of drought. Therefore, tracking changes in desert soil bacterial communities during rain events, in the field, was seldom attempted. Here, we assessed rain-mediated dynamics of active bacterial communities in the Negev Desert biological soil crust (biocrust). Biocrust samples were collected during, and after a medium rainfall and dry soil was used as a control; we evaluated the changes in active bacterial composition, potential function, potential photosynthetic activity, and extracellular polysaccharide (EPS) production. We hypothesized that rain would activate the biocrust phototrophs (mainly Cyanobacteria), while desiccation would inhibit their activity. In contrast, the biocrust Actinobacteria would decline during rewetting and revive with desiccation. Our results showed that hydration increased chlorophyll content and EPS production. As expected, biocrust rewetting activated Cyanobacteria, which replaced the former dominant Actinobacteria, boosting potential autotrophic functions. However, desiccation of the biocrust did not immediately change the bacterial composition or potential function and was followed by a delayed decrease in chlorophyll and EPS levels. This dramatic shift in the community upon rewetting led to modifications in ecosystem services. We propose that following a rain event, the response of the active bacterial community lagged behind the biocrust water content due to the production of EPS which delayed desiccation and temporarily sustained the biocrust community activity.

Spatial cover and carbon fluxes of urbanized Sonoran Desert biological soil crusts

Biological soil crusts (BSC) are important contributors to nutrient cycling in arid environments such as the Sonoran Desert. BSC at an urban (University Indian Ruins) and at a non-urban site (Santa Rita Experimental Range) were compared to determine if their structure or function was influenced by proximity to an urban environment. The Step Point method was used in the field to determine ground cover; which was found to be similar between sites. However, the spatial distribution of the BSCs was significantly different, such that more BSCs were found under plants at the non-urban site (P < 0.05). Relative gross photosynthesis was measured in the lab by addition of a watering event. Gross photosynthesis was found to be higher in the non-urban BSCs (P < 0.001), indicating lowered productivity in urban BSCs due to effects caused by proximity to urban environments. This study provides evidence that BSCs at urbanized sites are affected functionally, and therefore may be contributing differently to carbon and nitrogen cycling in these ecosystems.

Reference for different sensitivities of greenhouse gases effluxes to warming climate among types of desert biological soil crust

There is much uncertainty about how climate warming will impact greenhouse gases (GHG) budget in dry environments due to the lack of available data for desert biocrust soil. We implemented a 2.5-year field measurement of CO2, CH4 and N2O effluxes in cyanobacteria-dominated, moss-dominated and mixed (cyanobacteria, moss and lichen) biocrust soils using open-top-chambers to simulate climate warming (1.2 °C on average). Desert biocrust soils generally acted as a weak sink of atmospheric CH4 and N2O. Although warming effects on daily CO2, CH4, and N2O effluxes varied depending on sampling date and biocrust soil, there was no significant difference in daily, monthly and seasonal average CO2, CH4 and N2O effluxes between warming and control in most cases for three biocrust soils. However, warming caused a marginal (p = 0.06) decrease (14.2%) in annual accumulative CO2 efflux in moss-dominated biocrust soil due to the drought effects caused by warming indirectly and OTC sheltering of precipitation directly, while there was no significant difference between warming and control for cyanobacteria-dominated and mixed biocrust soils, implying a neutral response of GHG effluxes to climate warming. These results suggest that the GHG budget in arid desert biocrust soil would not be significantly changed in the warmer future when the direct negative effects of drought on CO2 effluxes were excluded. Therefore, a marginal decrease of accumulative CO2 effluxes in response to warming coupled with drought for moss-dominated biocrust soil might offer a weak negative feedback to warming and drier climate change pattern.

Changes in bacterial community composition and soil properties altered the response of soil respiration to rain addition in desert biological soil crusts

Soil water availability is the critical limitation for soil respiration (Rs) and subsequent ecosystem functions in biological soil crusts (BSCs) of arid ecosystems. Thus, uncovering the response mechanism of Rs to different precipitation regimes will improve our knowledge of the potential impacts of global climate change on this fragile ecosystem. To investigate the possible effects of altered precipitation regimes on bacterial community composition, soil properties and soil carbon effluxes, we implemented a 3-year field experiment in a desert shrub in northwestern China with manipulative precipitation treatments consisting of natural precipitation, that increased along a precipitation gradient of 5–40 mm during the growing season. Results showed that microbial biomass carbon and nitrogen (MBC and MBN) were significantly increased with increasing rainfall amount but soil organic carbon, total nitrogen, pH and biological thickness were relatively stable. Water addition significantly altered the bacterial community composition but not its diversity (including richness and evenness) by increasing the relative abundances of Actinobacteria and decreasing those of Bacteroidetes and Cyanobacteria. In addition, MBC was the primary driver that altered bacterial community composition. Soil physiochemical properties resulted in approximately 70% variations in Rs, whereas soil physicochemical properties and bacterial community composition impacted 10% variations in Rs. Our results indicated that bacterial community composition and soil physiochemical properties might be responsible for the responses of Rs to rainfall addition in BSCs of desert regions.

Properties of Modestobacter deserti sp. nov., a Kind of Novel Phosphate-Solubilizing Actinobacteria Inhabited in the Desert Biological Soil Crusts.

Three Gram-stain-positive, aerobic, motile actinobacterial strains designated as CPCC 205119T, CPCC 205215, and CPCC 205251 were isolated from different biological soil crust samples collected from Tengger Desert, China. The 16S rRNA gene sequence comparison of these three strains showed they had almost identical 16S rRNA genes, which were closely related to members of the family Geodermatophilaceae, with the highest similarities of 96.3–97.3% to the species of Modestobacter. In the phylogenetic tree based on 16S rRNA gene sequences, these isolates clustered into a subclade next to the branch containing the species of Modestobacter lapidis and Modestobacter multiseptatus, within the lineage of the genus Modestobacter. The comparative genomic characteristics (values of ANI, dDDH, AAI, and POCP) and the phenotypic properties (morphological, physiological, and chemotaxonomic characteristics) of these isolates readily supported to affiliate them to the genus Modestobacter as a single separate species. For which, we proposed that the isolates CPCC 205119T, CPCC 205215, and CPCC 205251 represent a novel species of the genus Modestobacter as Modestobacter deserti sp. nov. CPCC 205119T (=I12A-02624=NBRC 113528T=KCTC 49201T) is the type strain. The genome of strain CPCC 205119T consisted of one chromosome (4,843,235bp) containing 4,424 coding genes, 48 tRNA genes, five rRNA genes, three other ncRNA genes, and 101 pseudogenes, with G+C content of 74.7%. The whole-genome sequences analysis indicated that this species contained alkaline phosphatase genes (phoA/phoD), phosphate transport-related genes (phoU, phnC, phnD, phnE, phoB, phoH, phoP, phoR, pitH, ppk, pstA, pstB, pstC, and pstS), trehalose-phosphate synthase gene (otsA), trehalose 6-phosphate phosphatase gene (otsB) and other encoding genes for the properties that help the microorganisms to adapt to harsh environmental conditions prevalent in deserts. Strains of this species could solubilize tricalcium phosphate [Ca3(PO4)2] and phytin, assimilate pyrophosphate, thiophosphate, dithiophosphate, phosphoenol pyruvate, 2-deoxy-d-glucose-6-phosphate, and cysteamine-S-phosphate.

Reading and surviving the harsh conditions in desert biological soil crust: the cyanobacterial viewpoint.

Biological soil crusts (BSCs) are found in drylands, cover ∼12% of the Earth's surface in arid and semi-arid lands and their destruction is considered an important promoter of desertification. These crusts are formed by the adhesion of soil particles to polysaccharides excreted mostly by filamentous cyanobacteria, which are the pioneers and main primary producers in BSCs. Desert BSCs survive in one of the harshest environments on Earth, and are exposed to daily fluctuations of extreme conditions. The cyanobacteria inhabiting these habitats must precisely read the changing conditions and predict, for example, the forthcoming desiccation. Moreover, they evolved a comprehensive regulation of multiple adaptation strategies to enhance their stress tolerance. Here, we focus on what distinguishes cyanobacteria able to revive after dehydration from those that cannot. While important progress has been made in our understanding of physiological, biochemical and omics aspects, clarification of the sensing, signal transduction and responses enabling desiccation tolerance are just emerging. We plot the trajectory of current research and open questions ranging from general strategies and regulatory adaptations in the hydration/desiccation cycle, to recent advances in our understanding of photosynthetic adaptation. The acquired knowledge provides new insights to mitigate desertification and improve plant productivity under drought conditions.

Juggling Lightning: How Chlorella ohadii handles extreme energy inputs without damage.

The green alga Chlorella ohadii was isolated from a desert biological soil crust, one of the harshest environments on Earth. When grown under optimal laboratory settings it shows the fastest growth rate ever reported for a photosynthetic eukaryote and a complete resistance to photodamage even under unnaturally high light intensities. Here we examined the energy distribution along the photosynthetic pathway under four light and carbon regimes. This was performed using various methodologies such as membrane inlet mass spectrometer with stable O2 isotopes, variable fluorescence, electrochromic shift and fluorescence assessment of NADPH level, as well as the use of specific inhibitors. We show that the preceding illumination and CO2 level during growth strongly affect the energy dissipation strategies employed by the cell. For example, plastid terminal oxidase (PTOX) plays an important role in energy dissipation, particularly in high light- and low-CO2-grown cells. Of particular note is the reliance on PSII cyclic electron flow as an effective and flexible dissipation mechanism in all conditions tested. The energy management observed here may be unique to C. ohadii, as it is the only known organism to cope with such conditions. However, the strategies demonstrated may provide an insight into the processes necessary for photosynthesis under high-light conditions.

Life under quartz: Hypolithic mosses in the Mojave Desert.

Several species of dryland cyanobacteria are known to occur as hypoliths under semi-translucent rocks. In the Mojave Desert, these organisms find refuge from intense solar radiation under milky quartz where moisture persists for a longer period of time than in adjacent soil surface habitat. Desert mosses, which are extremely desiccation-tolerant, can also occur in these hypolithic spaces, though little is known about this unique moss microhabitat and how species composition compares to that of adjacent soil surface communities. To address this question, we deployed microclimate dataloggers and collected moss samples from under and adjacent to 18 milky quartz rocks (quartz mean center thickness 26 ± 15 mm) in a western high elevation Mojave Desert site. Light transmission through Mojave quartz rocks may be as low as 1.2%, and data from microclimate loggers deployed for five months support the hypothesis that quartz provides thermal buffering and higher relative humidity compared to the soil surface. Of the 53 samples collected from hypolith and surface microhabitats, 68% were Syntrichia caninervis, the dominant bryophyte of the Mojave Desert biological soil crust. Tortula inermis accounted for 28% of the samples and 4% were Bryum argenteum. In a comparison of moss community composition, we found that S. caninervis was more likely to be on the soil surface, though it was abundant in both microhabitats, while T. inermis was more restricted to hypoliths, perhaps due to protection from temperature extremes. In our study site, the differences between hypolithic and surface microhabitats enable niche partitioning between T. inermis and S. caninervis, enhancing alpha diversity. This work points to the need to thoroughly consider microhabitats when assessing bryophyte species diversity and modelling species distributions. This focus is particularly important in extreme environments, where mosses may find refuge from the prevailing macroclimatic conditions in microhabitats such as hypoliths.

MicroNiche: an R package for assessing microbial niche breadth and overlap from amplicon sequencing data.

Niche is a fundamental concept in ecology. It integrates the sum of biotic and abiotic environmental requirements that determines a taxon's distribution. Microbiologists currently lack quantitative approaches to address niche-related hypotheses. We tested four approaches for the quantification of niche breadth and overlap of taxa in amplicon sequencing datasets, with the goal of determining generalists, specialists and environmental-dependent distributions of community members. We applied these indices to in silico training datasets first, and then to real human gut and desert biological soil crust (biocrust) case studies, assessing the agreement of the indices with previous findings. Implementation of each approach successfully identified a priori conditions within in silico training data, and we found that by including a limit of quantification based on species rank, one could identify taxa falsely classified as specialists because of their low, sparse counts. Analysis of the human gut study offered quantitative support for Bacilli, Gammaproteobacteria and Fusobacteria specialists enriched after bariatric surgery. We could quantitatively characterise differential niche distributions of cyanobacterial taxa with respect to precipitation gradients in biocrusts. We conclude that these approaches, made publicly available as an R package (MicroNiche), represent useful tools to assess microbial environment-taxon and taxon-taxon relationships in a quantitative manner.

Dictyosphaerium-like morphotype in terrestrial algae: what is Xerochlorella (Trebouxiophyceae, Chlorophyta)?1.

Several strains of terrestrial algae isolated from biological soil crusts in Germany and Ukraine were identified by morphological methods as the widely distributed species Dictyosphaerium minutum (=Dictyosphaerium chlorelloides). Investigation of the phylogeny showed their position unexpectedly outside of Chlorellaceae (Trebouxiophyceae) and distantly from Chlorella chlorelloides, to which this taxon was attributed after revision of the genus Chlorella based on an integrative approach. SSU rRNA phylogeny determined the position of our strains inside a clade recently described as a new genus of the cryptic alga Xerochlorella olmiae isolated from desert biological soil crusts in the United States. Investigation of the morphology of the authentic strain of X. olmiae showed Dictyosphaerium‐like morphology, as well as some other characters, common for our strains and morphospecies D. minutum. The latter alga was described as terrestrial and subsequently united with the earlier described aquatic representative D. chlorelloides because of their similar morphology. The revision of Chlorella mentioned above provided only one aquatic strain (D. chlorelloides), which determined its position in the genus. But terrestrial strains of the morphospecies were not investigated phylogenetically. Our study showed that the terrestrial D. minutum is not related to the morphologically similar D. chlorelloides (=Chlorella chlorelloides, Chlorellaceae), and instead represented a separate lineage in the Trebouxiophyceae, recently described as genus Xerochlorella. Therefore, revision of Xerochlorella is proposed, including nomenclatural combinations, epitypifications, and emendations of two species: X. minuta and X. dichotoma. New characters of the genus based on investigation of morphology and ultrastructure were determined.

Dynamic expression of intra- and extra-cellular proteome and the influence of epiphytic bacteria for Nostoc flagelliforme in response to rehydration.

Nostoc flagelliforme is well known for its strong ecological adaptability in inhabiting desert biological soil crusts. However, the mechanism of its recovery from quiescent to active state after prolonged dormancy remains poorly characterized. Especially how exoproteome be related to the adaptive strategies and participate in the microalgae-bacteria interaction. In the present work, we analysed the intra- and extra-cellular proteome of N. flagelliforme over a complete rehydration period both in sterilization and in natural condition for the first time. The protein expression profile for N. flagelliforme has more fluctuations during the first 1 h after wetting but been relatively steady after fully hydrated. According to the extracellular proteomic datasets, we found a dynamic secretion of various extracellular hydrolytic enzymes and membrane transport proteins, which were related to peptidoglycan digestion and nutrient exchange respectively. Two-hundred and thirteen differentially expressed proteins induced by sterilization also reflect variation in nutrient exchange and highlight symbiosis between N. flagelliforme and surrounding bacteria. We also identified 112 phosphopeptides and 217 phosphorylation site of 95 protein of hydrated N. flagelliforme. The time course datasets we present here will be a reference for understanding the molecular processes underlying N. flagelliforme resuscitation and its potential role in microbial community diversification and soil desertification control.

Bacterial Communities of Mojave Desert Biological Soil Crusts Are Shaped by Dominant Photoautotrophs and the Presence of Hypolithic Niches

Biocrust communities are often heterogeneous and affected by small-scale physical and environmental factors. The presence of moss in biocrusts, for example, is likely to create a set of physical conditions distinct from those found in biocrusts that lack mosses. Similarly, hypolithic organisms living under and on the belowground surface of translucent and opaque stones (typically quartz) experience a distinct environment relative to surrounding soil surface organisms. To understand the impact of these factors on biocrust bacterial community composition, we performed 16S rRNA sequencing from surface and hypolithic biocrusts with and without the common biocrust moss, Syntrichia caninervis. While alpha diversity indices did not differ significantly between any of the biocrust habitats sampled, we did observe differences in overall community composition. Cyanobacterial abundance and diversity decreased in the presence of moss and in surface samples compared to hypolithic biocrusts, while Proteobacteria showed the opposite pattern. Acidobacteria were significantly more abundant in hypolithic niches, and Patescibacteria were found to be restricted to moss-dominated surface biocrusts. Notably, bacterial community composition was found to shift significantly between surface and hypolithic biocrusts lacking moss (Adonis, R2 = 0.122, p = 0.002) and between surface moss and non-moss biocrusts (R2 = 0.107, p = 0.002). These findings support the idea that even at small spatial scales (e.g., within < 10 cm), desert biocrust bacterial community composition varies based on the habitat structure and cohabitants.

Learning representations of microbe-metabolite interactions.

Integrating multi-omics datasets is critical for microbiome research, but multiple statistical challenges can confound traditional correlation techniques. We solve this problem by using neural networks to estimate the conditional probability that each molecule is present given the presence of each specific microbe. We show with known environmental (desert biological soil crust wetting) and clinical (cystic fibrosis lung) examples, our ability to recover microbe-metabolite relationships, and demonstrate how the method can discover relationships between microbially-produced metabolites and inflammatory bowel disease.

Desert cyanobacteria prepare in advance for dehydration and rewetting: The role of light and temperature sensing.

Cyanobacteria inhabiting desert biological soil crusts must prepare towards dehydration, or their revival after rewetting is severely impaired. The mechanisms involved are unknown but signalling of forthcoming dehydration by dawn illumination was demonstrated. Accurate and reproducible simulation of desert conditions enabled examination of physiological activities and transcript profiles in a model organism, Leptolyngbya ohadii, in response to specific conditions. Exposure to far red light or lack of ground warming during dawn severely reduced revival after rewetting and altered the network of gene expression. The data implicated phytochromes in light and temperature sensing. Many genes were up- or down-regulated before water content decline, while others were strongly affected by the progression of dehydration and desiccation. Transcription continues during the desiccated phase but only barely during early rewetting, although photosynthetic activity was regained. Application of rifampicin with or without a preceding dehydration phase demonstrated that RNA is stabilized/protected during desiccation, possibly by intrinsically disordered proteins. We conclude that increasing light and temperature at dawn activates a network of genes that prepare the cells towards dehydration. Quick resumption of photosynthesis upon rewetting in contrast to the slow change in the transcript profile suggested that in addition to preparing towards dehydration the cells also prepare for forthcoming rewetting, during dehydration. Unravelling the presently unknown function of many responding genes will help to clarify the networks involved.

Resource utilization of microalgae from biological soil crusts: Biodiesel production associated with desertification control

With the continuing consumption of resources and increasingly prominent environmental issues, microalgal resource utilization has received extensive attention. In this study, based on the microalgal investigation in desert biological soil crusts (BSCs) using pyrosequencing technology, the cultivated crust microalgae were further isolated in order to obtain high quality microalgae for resource utilization. The results showed that with crust development and succession, microalgal diversity gradually decreased, including the number of operational taxonomic units (OTUs) and genus, although Microcoleus always was the dominant genera. Pyrosequencing obtained 630 OTUs of cyanobacteria, 25 OTUs of green algae and 9 OTUs of diatom; however, part of cultivated microalgae still could not yet be detected due to the DNA extraction preferences and errors caused by PCR amplification. After isolation, four strains were purified and cultivated, including two filamentous cyanobacteria Microcoleus vaginatus BSC-06 and Scytonema javanicum BSC-39, and two unicellular green algae Chlorella sp. BSC-24 and Monoraphidium dybowskii BSC-81. The two green algae grew fast (>250 mg L-1 d-1), and achieved high lipid productivity up to 75–85 mg L-1 d-1, with lipid content of 28.7–39.0%, thus was considered as promising feedstock for biodiesel production. In addition, the two crust cyanobacteria could be used to construct artificial cyanobacterial soil crusts in desertification control, although their biomass accumulation was not as high as that in the green algae. Ultimately, combining biodiesel production with desertification control would not only improve desert environments, but also provide ideal places for the local microalgal resource exploitation, further promoting desert socioeconomic development.

Flux balance modeling to predict bacterial survival during pulsed-activity events

Abstract. Desert biological soil crusts (BSCs) are cyanobacteria-dominated surface soil microbial communities common to plant interspaces in arid environments. The capability to significantly dampen their metabolism allows them to exist for extended periods in a desiccated dormant state that is highly robust to environmental stresses. However, within minutes of wetting, metabolic functions reboot, maximizing activity during infrequent permissive periods. Microcoleus vaginatus, a primary producer within the crust ecosystem and an early colonizer, initiates crust formation by binding particles in the upper layer of soil via exopolysaccharides, making microbial dominated biological soil crusts highly dependent on the viability of this organism. Previous studies have suggested that biopolymers play a central role in the survival of this organism by powering resuscitation, rapidly forming compatible solutes, and fueling metabolic activity in dark, hydrated conditions. To elucidate the mechanism of this phenomenon and provide a basis for future modeling of BSCs, we developed a manually curated, genome-scale metabolic model of Microcoleus vaginatus (iNJ1153). To validate this model, gas chromatography–mass spectroscopy (GC–MS) and liquid chromatography–mass spectroscopy (LC–MS) were used to characterize the rate of biopolymer accumulation and depletion in in hydrated Microcoleus vaginatus under light and dark conditions. Constraint-based flux balance analysis showed agreement between model predictions and experimental reaction fluxes. A significant amount of consumed carbon and light energy is invested into storage molecules glycogen and polyphosphate, while β-polyhydroxybutyrate may function as a secondary resource. Pseudo-steady-state modeling suggests that glycogen, the primary carbon source with the fastest depletion rate, will be exhausted if M. vaginatus experiences dark wetting events 4 times longer than light wetting events.

The role of non-rainfall water on physiological activation in desert biological soil crusts

Non-rainfall water (NRW, e.g. fog and dew), in addition to rainfall and snowfall, are considered important water inputs to drylands. At the same time, biological soil crusts (BSCs) are important components of drylands. However, little information is available regarding the effect of NRW inputs on BSC activation. In this study, the effects of NRW on physiological activation in three BSC successional stages, including the cyanobacteria crust stage (Crust-C), moss colonization stage (Crust-CM), and moss crust stage (Crust-M), were studied in situ. Results suggest NRW inputs hydrated and activated physiological activity (Fv/Fm, carbon exchange, and nitrogen fixation) in BSCs but led to a negative carbon balance and low rates of nitrogen fixation in BSCs. One effective NRW event could hydrate BSCs for 7 h. Following simulated rainfall, the physiological activities recovered within 3 h, and net carbon gain occurred until 3 h after hydration, whereas NRW-induced physiological recovery processes were slower and exhibited lower activities, leading to a negative carbon balance. There were significant positive correlations between NRW amounts and the recovered values of Fv/Fm in all the three BSC stages (p < .001). The thresholds for Fv/Fm activation decreased with BSC succession, and the annual effective NRW events increased with BSC succession, with values of 29.8, 89.2, and 110.7 in Crust-C, Crust-CM and Crust-M, respectively. The results suggest that moss crust and moss-cyanobacteria crust use NRW to prolong metabolic activity and reduce drought stress more efficiently than cyanobacteria crusts. Therefore, these results suggest that BSCs utilize NRW to sustain life while growth and biomass accumulation require precipitation (rainfall) events over a certain threshold.