Search for: All records

ABSTRACT Desert kangaroo rats (Dipodomys deserti) construct burrows that can create micro-niches favorable to increased microbial activity. The aim of this study was to characterize the bacterial communities found in kangaroo rat burrows, in proximal desert surface sand, and in samples from kangaroo rats. We collected samples from burrow ceilings of actively inhabited burrows, from burrows that were no longer in use, and from the proximal surface sand in the Sonoran Desert, Yuma, AZ. Following DNA extraction from samples, 16S rRNA gene sequencing was performed, and functional predictions were made and assessed for each characterized bacterial community. Active burrow samples exhibited greater alpha diversity but similar beta diversity when compared to surface sand (P< 0.05), with no significant differences observed between abandoned and active burrows. Bacterial genera and genes related to nitrogen fixation, nitrification, and urea hydrolysis were found in significantly higher abundance in active burrows compared to the surface sand (P< 0.05). The core microbiome of active burrow samples was different from surface sand, including higher abundances ofAcidimicrobialesandAcidobacteriasubdivision Gp7. Active burrow samples included 30 unique genera. Kangaroo rat anal swabs shared 12, cheek pouches shared 6 unique genera with burrows. These findings suggest that kangaroo rats can shape the microbial composition of their burrow environment through the introduction of food material and waste, facilitating increased species richness and bacterial diversity.IMPORTANCEAnimals can alter soil parameters, including microbial composition through burrowing activities, excretion, and dietary composition. Desert kangaroo rats (Dipodomys deserti) construct burrows within loose desert sand that have microclimatic conditions different from the surrounding desert climate. In this study, we explored the effect of disturbance from kangaroo rat activities on the bacterial composition of sand. We compared the bacterial community compositions of kangaroo rat (D. deserti) samples, their burrows, and the proximal surface sand. The results showed that burrow sand shows higher richness and diversity of bacterial community with higher abundances of bacterial genera and genes associated with nitrogen fixation, nitrification, and urea hydrolysis compared to the surface sand. These findings suggest that kangaroo rats affect the microbial composition of their burrow environment through the introduction of food material and waste. 

Cefotaximase-Munich (CTX-M) extended-spectrum beta-lactamases (ESBLs) are commonly associated with Gram-negative, hospital-acquired infections worldwide. Several beta-lactamase inhibitors, such as clavulanate, are used to inhibit the activity of these enzymes. To understand the mechanism of CTX-M-15 activity, we have determined the crystal structures of CTX-M-15 in complex with two specific classes of beta-lactam compounds, desfuroylceftiofur (DFC) and ampicillin, and an inhibitor, clavulanic acid. The crystal structures revealed that Ser70 and five other residues (Lys73, Tyr105, Glu166, Ser130, and Ser237) participate in catalysis and binding of those compounds. Based on analysis of steady-state kinetics, thermodynamic data, and molecular docking to both wild-type and S70A mutant structures, we determined that CTX-M-15 has a similar affinity for all beta-lactam compounds (ceftiofur, nitrocefin, DFC, and ampicillin), but with lower affinity for clavulanic acid. A catalytic mechanism for tested β-lactams and two-step inhibition mechanism of clavulanic acid were proposed. CTX-M-15 showed a higher activity toward DFC and nitrocefin, but significantly lower activity toward ampicillin and ceftiofur. The interaction between CTX-M-15 and both ampicillin and ceftiofur displayed a higher entropic but lower enthalpic effect, compared with DFC and nitrocefin. DFC, a metabolite of ceftiofur, displayed lower entropy and higher enthalpy than ceftiofur. This finding suggests that compounds containing amine moiety (e.g., ampicillin) and the furfural moiety (e.g., ceftiofur) could hinder the hydrolytic activity of CTX-M-15.