Highlights d Cities possess a consistent ''core'' set of non-human microbes d Urban microbiomes echo important features of cities and city-life d Antimicrobial resistance genes are widespread in cities d Cities contain many novel bacterial and viral species

Veterans of the 1990-1991 Gulf War have been reported to have an increased incidence of amyotrophic lateral sclerosis (ALS) compared to personnel who were not deployed. An excess of ALS cases was diagnosed in Gulf War veterans younger than 45 years of age. Increased ALS among Gulf War veterans appears to be an outbreak time-limited to the decade following the Gulf War. Seeking to identify biologically plausible environmental exposures, we have focused on inhalation of cyanobacteria and cyanotoxins carried by dust in the Gulf region, particularly Qatar. Cyanobacterial crusts and mats are widespread in the deserts of Qatar, occupying up to 56% of the available area in some microhabitats. These cyanobacterial crusts, which help bind the desert sands, are dormant throughout most of the year, but during brief spring rains actively photosynthesize. When disturbed by vehicular traffic or other military activities, the dried crusts and mats can produce significant dust. Using HPLC/FD, an amino acid analyzer, UPLC/MS, and triple quadrupole LC/MS/MS we find that the dried crusts and mats contain neurotoxic cyanobacterial toxins, including beta-N-methylamino-L-alanine (BMAA) and 2,4 diaminobutyric acid (DAB). If dust containing cyanobacteria is inhaled, significant exposure to BMAA and other cyanotoxins may occur. We suggest that inhalation of BMAA, DAB, and other aerosolized cyanotoxins may constitute a significant risk factor for the development of ALS and other neurodegenerative diseases.

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Climbing stems in the rattan genus Calamus can reach lengths of well over 100 m, are long-lived, and yet their vascular tissue is entirely primary. Such a combination suggests that stem vasculature is efficient and resistant to hydraulic disruption. By means of an optical shuttle and video recording of sequential images we analyzed the stem of a cultivated species. The stem has vascular features that are unusual compared with those in arborescent palms and seemingly inefficient in terms of long-distance water transport. Axial bundles are discontinuous basally because leaf traces, when followed downwards, always end blindly below. Furthermore, there is no regular distal branching of each leaf trace at its level of departure into a leaf, so that neither a continuing axial bundle nor bridges to adjacent axial bundles are produced as in the standard palm construction. Instead, the axial bundles in the stem periphery are connected to leaf traces and to each other by narrow and irregular transverse or oblique commissures that are not the developmental homologues of bridges. As in other palms, metaxylem within a leaf trace is not continuous into the leaf so that the only connection to a leaf is via protoxylem. Within the stem, protoxylem (tracheids) and metaxylem (vessels) are never contiguous, unlike in other palms, which suggests that water can only move from metaxylem to protoxylem, and hence into the leaf, across a hydraulic resistance. We suggest that this minimizes cavitation of vessels and/or may be associated with an unknown mechanism that refills embolized vessels. Also, the metaxylem can be significant in stem water storage in the absence of abundant ground parenchyma.

[1] Although microorganisms play an important role in biological soil crusts and plant rhizospheres in deserts, it is unclear whether temperature and moisture deep within relatively fast moving hyperarid mobile dunes present a suitable habitat for microbes. To inform this question, we report measurements of temperature and humidity from probes initially sunk below the leeward avalanche face of a mobile barchan dune in the Qatar desert, emerging windward after 15 months of deep burial. Despite large diurnal variations on the surface, temperature within this dune of 5.6 m height is predictable, as long as dune advection is properly considered. It evolves on smaller amplitude and longer timescale than the surface, lagging average seasonal atmospheric conditions by about 2 months. We contrast these deep thermal records with measurements of diurnal variations of the temperature profile just below the surface, which we calculate with a thermal model predicting the relative roles of wind-driven convective heat transfer and net radiation flux on the dune. Observations and analyses also suggest why random precipitation on the leeward face produces a more unpredictable moisture patchwork on the windward slope. By rapidly reaching sheltered depths, small quantities of rain falling on that face escape evaporation and endure within the dune until resurfacing upwind. At depths below 10 cm, we show that moisture, rather than temperature, determines the viability of microbes and we provide initial microscopic and respiration-based evidence of their presence below the windward slope.