The evolution of Crassulacean acid metabolism (CAM) is thought to be along a C3-CAM continuum including multiple variations of CAM such as CAM cycling and CAM idling. Here, we applied large-scale constraint-based modeling to investigate the metabolism and energetics of plants operating in C3, CAM, CAM cycling, and CAM idling. Our modeling results suggested that CAM cycling and CAM idling could be potential evolutionary intermediates in CAM evolution by establishing a starch/sugar-malate cycle. Our model analysis showed that by varying CO2 exchange during the light period, as a proxy of stomatal conductance, there exists a C3-CAM continuum with gradual metabolic changes, supporting the notion that evolution of CAM from C3 could occur solely through incremental changes in metabolic fluxes. Along the C3-CAM continuum, our model predicted changes in metabolic fluxes not only through the starch/sugar-malate cycle that is involved in CAM photosynthetic CO2 fixation but also other metabolic processes including the mitochondrial electron transport chain and the tricarboxylate acid cycle at night. These predictions could guide engineering efforts in introducing CAM into C3 crops for improved water use efficiency.

While the wide-spectrum antimicrobial properties and stability of silver nanomaterials have been copiously utilized in many medical and consumer products, we found that Methicillin Resistant Staphylococcus aureus (MRSA) is less susceptible to silver in comparison to Methicillin Sensitive Staphylococcus aureus (MSSA). Pre-exposure of MRSA to sub-lethal concentrations of AgNO3 caused 2.5-fold increase in LD50 of silver suggesting an inducible resistance mechanism. Studies involving gene expression profiling and efflux pump blockers showed the induction of P-type efflux pumps (Cop A, Cop Z and Nor B) as the principle mechanism conferring silver resistance in MRSA. Chlorpromazine—an efflux pump blocker increased sensitivity of MRSA to silver. Leveraging on these observations, silver resistance in MRSA was circumvented by enhancing the bioavailability of silver by cationic functioning of silver nanoparticles or by co-delivering silver together with chlorpromazine. Atomic Force Microscopy showed that poly-ethylene imine (PEI) functionalized silver nanoparticles adhere to bacterial cells which was found to increase the bioavailability, membrane rupture and cell death. The strategy of co-delivery of AgNO3 and chlorpromazine using chitosan-functionalized wormhole silica nanoparticles caused 12 log reduction in bacterial count which was 1000 times higher than bacterial reduction by AgNO3 alone. In short, these studies showed that circumventing antimicrobial resistance in pathogenic bacteria is possible by designed silver nanotechnology.

13The evolution of Crassulacean acid metabolism (CAM) is thought to be along a C 3 -CAM 14 continuum including multiple variations of CAM such as CAM cycling and CAM idling. Here, 15we applied large-scale constraint-based modelling to investigate the metabolism and energetics 16 of plants operating in C 3 , CAM, CAM cycling and CAM idling. Our modelling results suggested 17 that CAM cycling and CAM idling could be potential evolutionary intermediates in CAM 18 evolution by establishing a starch/sugar-malate cycle. Our model analysis showed that by 19 varying CO 2 exchange during the light period, as a proxy of stomatal conductance, there exists a 20 C 3 -CAM continuum with gradual metabolic changes, supporting the notion that evolution of 21 CAM from C 3 could occur solely through incremental changes in metabolic fluxes. Along the 22 C 3 -CAM continuum, our model predicted changes in metabolic fluxes not only through the 23 starch/sugar-malate cycle that is involved in CAM photosynthetic CO 2 fixation but also other 24 metabolic processes including the mitochondrial electron transport chain and the tricarboxylate 25 acid cycle at night. These predictions could guide engineering efforts in introducing CAM into 26 C 3 crops for improved water use efficiency. 27 28 Key words 29 CAM cycling, CAM evolution, CAM idling, Crassulacean acid metabolism, metabolic 30 modelling, flux balance analysis 31