Effect of preconditioning to the soil environment on the performance of 20 cyanobacterial strains used as inoculum for biocrust restoration

The Microbiology of Biological Soil Crusts

Biological soil crusts are thin, inconspicuous communities along the soil atmosphere ecotone that, until recently, were unrecognized by ecologists and even more so by microbiologists. In its broadest meaning, the term biological soil crust (or biocrust) encompasses a variety of communities that develop on soil surfaces and are powered by photosynthetic primary producers other than higher plants: cyanobacteria, microalgae, and cryptogams like lichens and mosses. Arid land biocrusts are the most studied, but biocrusts also exist in other settings where plant development is constrained. The minimal requirement is that light impinge directly on the soil; this is impeded by the accumulation of plant litter where plants abound. Since scientists started paying attention, much has been learned about their microbial communities, their composition, ecological extent, and biogeochemical roles, about how they alter the physical behavior of soils, and even how they inform an understanding of early life on land. This has opened new avenues for ecological restoration and agriculture.

Climate dictates microbial community composition and diversity in Australian biological soil crusts (biocrusts)

The soil surface of drylands can typically be colonized by cyanobacteria and other microbes, forming biological soil crusts or 'biocrusts'. Biocrusts provide critical benefits to ecosystems and are a common component of the largely arid and semi-arid Australian continent. Yet, their distribution and the parameters that shape their microbial composition have not been investigated. We present here the first detailed description of Australia's biocrust microbiome assessed from 15 sites across the continent using 16S rRNA sequencing. The most abundant bacterial phyla from all sites were Cyanobacteria, Proteobacteria, Actinobacteria, Chloroflexi and Bacteroidetes. Cyanobacterial communities from northern regions were more diverse and unclassified cyanobacteria were a noticeable feature of northern biocrusts. Segregation between northern and southern regions was largely due to the differential abundance of Microcoleus spp., with M. paludosus dominating in the north and M. vaginatus dominating in the south. The geographical shifts in bacterial composition and diversity were correlated to seasonal temperatures and summer rainfall. Our findings provide an initial reference for sampling strategies to maximize access to bacterial genetic diversity. As hubs for essential ecosystem services, further investigation into biocrusts in arid and semi-arid regions may yield discoveries of genetic mechanisms that combat increases in warming due to climate change.

Salty Twins: Salt-Tolerance of Terrestrial Cyanocohniella Strains (Cyanobacteria) and Description of C. rudolphia sp. nov. Point towards a Marine Origin of the Genus and Terrestrial Long Distance Dispersal Patterns

The ability to adapt to wide ranges of environmental conditions coupled with their long evolution has allowed cyanobacteria to colonize almost every habitat on Earth. Modern taxonomy tries to track not only this diversification process but also to assign individual cyanobacteria to specific niches. It was our aim to work out a potential niche concept for the genus Cyanocohniella in terms of salt tolerance. We used a strain based on the description of C. rudolphia sp. nov. isolated from a potash tailing pile (Germany) and for comparison C. crotaloides that was isolated from sandy beaches (The Netherlands). The taxonomic position of C. rudolphia sp. nov. was evaluated by phylogenetic analysis and morphological descriptions of its life cycle. Salt tolerance of C. rudolphia sp. nov. and C. crotaloides was monitored with cultivation assays in liquid medium and on sand under salt concentrations ranging from 0% to 12% (1500 mM) NaCl. Optimum growth conditions were detected for both strains at 4% (500 mM) NaCl based on morpho-anatomical and physiological criteria such as photosynthetic yield by chlorophyll a fluorescence measurements. Taking into consideration that all known strains of this genus colonize salty habitats supports our assumption that the genus might have a marine origin but also expands colonization to salty terrestrial habitats. This aspect is further discussed, including the ecological and biotechnological relevance of the data presented.

Beneficial cyanosphere heterotrophs accelerate establishment of cyanobacterial biocrust

Biological soil crusts (biocrusts) are communities of microbes that inhabit the surface of arid soils and provide essential services to dryland ecosystems. While resistant to extreme environmental conditions, biocrusts are susceptible to anthropogenic disturbances that can deprive ecosystems of these valuable services for decades. Until recently, culture-based efforts to produce inoculum for cyanobacterial biocrust restoration in the Southwestern US focused on producing and inoculating the most abundant primary producers and biocrust pioneers, Microcoleus vaginatus and members of the family Coleofasciculaceae (aka "Microcoleus streenstrupii complex"). The discovery that a unique microbial community characterized by diazotrophs is intimately associated with M. vaginatus, known as the "cyanosphere", suggests a symbiotic division of labor in which nutrients are traded between phototrophs and heterotrophs. To probe the potential use of such cyanosphere members in the restoration of biocrusts, we performed co-inoculations of soil substrates with cyanosphere constituents. This resulted in more rapid cyanobacterial growth over inoculations with the cyanobacterium alone. Additionally, we found that the mere addition of beneficial heterotrophs enhanced the formation of a cohesive biocrust without the need of additional phototrophic biomass within native soils that contain trace amounts of biocrust cyanobacteria. Our findings support the hitherto unknown role of beneficial heterotrophic bacteria in the establishment and growth of biocrusts and allow us to make recommendations concerning biocrust restoration efforts based on the presence of remnant biocrust communities in disturbed areas. Future biocrust restoration efforts should consider cyanobacteria and their beneficial heterotrophic community as inoculants. Importance The advancement of biocrust restoration methodologies for cyanobacterial biocrusts has been largely achieved through trial and error. Successes and failures could not always be traced back to particular factors. The investigation and application of foundational microbial interactions existing within biocrust communities is a crucial step toward informed and repeatable biocrust restoration methodologies.

A Fog-Irrigated Soil Substrate System Unifies and Optimizes Cyanobacterial Biocrust Inoculum Production

Biological soil crusts (biocrusts) are globally important microbial communities inhabiting the top layer of soils. They provide multiple services to dryland ecosystems but are particularly vulnerable to anthropogenic disturbance from which they naturally recover only slowly. Assisted inoculation with cyanobacteria is held as a promising approach to promote biocrust regeneration. Two different methodologies have been developed for this purpose: mass cultivation of biocrust pioneer species (such as the cyanobacteria Microcoleus spp.) on cellulose supports, and polymicrobial cultivation of biocrusts in soils within greenhouse settings. Here, we aimed to test a novel method to grow cyanobacterial biocrust inoculum based on fog irrigation of soil substrates (FISS) that can be used with either culture-based or mixed-community approaches. We found that the FISS system presents clear advantages over previous inoculum production methodologies; overall, FISS eliminates the need for specialized facilities and decreases user effort. Specifically, there were increased microbial yields and simplification of design compared to those of the culture-based and mixed-community approaches, respectively. Its testing also allows us to make recommendations on underexplored aspects of biocrust restoration: (i) field inoculation levels should be equal to or greater than the biomass found in the substrate and (ii) practices regarding evaluation of cyanobacterial biomass should, under certain circumstances, include proxies additional to chlorophyll a IMPORTANCE Biocrust inoculum production for use in dryland rehabilitation is a powerful tool in combating the degradation of dryland ecosystems. However, the facilities and effort required to produce high-quality inoculum are often a barrier to effective large-scale implementation by land managers. By unifying and optimizing the two foremost methods for cyanobacterial biocrust inoculum production, our work improves on the ease and cost with which biocrust restoration technology can be translated to practical widespread implementation.