Microbes in hot desert soil partake in core ecosystem processes e.g., biogeochemical cycling of carbon.
Nevertheless, there is still a fundamental lack of insights regarding short-term (i.e., over a 24-hour
[diel] cycle) microbial responses to highly fluctuating microenvironmental parameters like temperature
and humidity. To address this, we employed T-RFLP fingerprinting and 454 pyrosequencing of 16S
rRNA-derived cDNA to characterize potentially active bacteria in Namib Desert soil over multiple diel
cycles. Strikingly, we found that significant shifts in active bacterial groups could occur over a single
24-hour period. For instance, members of the predominant Actinobacteria phyla exhibited a significant
reduction in relative activity from morning to night, whereas many Proteobacterial groups displayed
an opposite trend. Contrary to our leading hypothesis, environmental parameters could only account
for 10.5% of the recorded total variation. Potential biotic associations shown through co-occurrence
networks indicated that non-random inter- and intra-phyla associations were ‘time-of-day-dependent’
which may constitute a key feature of this system. Notably, many cyanobacterial groups were
positioned outside and/or between highly interconnected bacterial associations (modules); possibly
acting as inter-module ‘hubs’ orchestrating interactions between important functional consortia.
Overall, these results provide empirical evidence that bacterial communities in hot desert soils exhibit
complex and diel-dependent inter-community associations.