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

Abstract

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 eld 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 before, during, and after a heavy rainfall; we evaluated the changes in active bacterial composition, potential function, photosynthetic activity, and extracellular polysaccharides (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 modi cations in the 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.

Hyperarid soil microbial community response to simulated rainfall

“…The structure of the microbial communities at the phylum level remained stable after hydration ( Figure 3 ). This response is distinct from that observed with biocrusts from a hyperarid region in the Negev Desert, where a drastic collapse of Actinobacteriota occurred ( Angel and Conrad, 2013 ; Baubin et al, 2022 ). Despite community stability at the phylum level, dynamic, but distinct shifts were observed within the actinobacterial community for both the YUN1242 and YUN1609 soil microbiomes.…”

Phototrophic Nitrogen Fixation, a Neglected Biogeochemical Process in Mine Tailings?

“…sinensis. Biocrusts are globally occurring phototroph-driven microbial communities composed primarily of Cyanobacteria, lichens, mosses, algae, and heterotrophic organisms, forming the zone of nutrient accumulation and transformation. , They are pioneers in the colonization and succession of bare grounds, serving as food source for plants, animals, and other organisms in often oligotrophic dryland ecosystems. − High rates of nitrogen fixation were frequently seen in biocrust. − Given the elevated phototrophic nitrogenase activities and enriched abundances of Roseomonas in the rhizosphere of biocrust and M. sinensis, it is fair to propose that Roseomonas spp.…”

A desiccated dual-species subaerial biofilm reprograms its metabolism and affects water dynamics in limestone

“…First, the inhibition of photosynthesis reduced the level of oxidative stress because the photosynthetic machinery is a major source of ROS (Raanan et al, 2016). Second, when responding to an increase in ROS concentration, the desiccated SABs possibly activated various regulators that modulate the transcription of genes involved in ROS scavenging and DNA repair (Baubin et al, 2022). An increase in antioxidant enzyme synthesis is typically a response to dehydration, however, the synthesized enzymes and the extent of the synthesis vary with species (Kranner et al, 2008).…”

“…Thus, the desiccated SABs recover their activities quickly after reaching a critical relative humidity. SABs respond quickly and efficiently to hydration by exploiting this short window of opportunity to secure the nutrients (Baubin et al, 2022). The water was possibly formed, at least partially, by the deliquescence of salts, a process when hygroscopic salts absorb ambient water vapor and form a saturated brine.…”