Nutritional Strategies and Nutrient Acquisition

• Nutritional Strategies (Types)– Required Resources– Nutritional Types

• Nutrition Acquisition– Passive transport– Active transport– “Scavenging”

Resources for All Life:• Energy: cells need to do the work of membrane transport,

biosynthesis, and mechanical processes.

• Electrons: anabolic reactions (biosynthesis) require reducing power (adding e-).

• Major Elements (macronutrients): Carbon, Nitrogen, Phosphorous in varying proportions (e.g. C:N:P ratio of eukaryote algae ≈ 106:16:1; bacteria ≈ 100:25:1; fungi ≈ 400:20:1). These, along with O, H and S, are all supplied in organic or inorganic form. In lesser amounts are Fe, Mg, Ca, K, and Na, which are mostly supplied as inorganic forms.

• Trace Elements (micronutrients): Mn, Zn, Co, Cu, Mo, & Ni.

• Growth Factors: essential amino acids, vitamins, and nucleoside bases are needed for growth but cannot be made by many organisms; some are sources of macro- and micro- nutrients

Major Nutritional Types: (see Table 5.2)

Energy → Electrons → Carbon

• Photolithoautotrophy

• Photoorganoheterotrophy

• Chemolithoautotrophy

• Chemoorganoheterotrophy

• Both follow a concentration gradient, high to low; therefore reversible.

• Passively through membrane lipids or porins; rate increase linear.

• Facilitated by selective transporters; rate increase with [S] then plateaus at “saturation”.

Transport Types:Passive Diffusion

Facilitated Diffusion

Transport Types:Primary Active Transport

ATP-Binding Cassette Transporter (ABC transporter)

• Against concentration gradient requires energy.

• “Primary” transporters directly use ATP for energy.

• May require solute binding proteins to scavenge solute.

Transport Types:

Secondary Active Transport

• Solute transport against a concentration gradient.

• Secondary transporter couples solute with a flow of protons or other ions along strong concentration gradients; energy source.

• Mechanism may be antiport or symport.

Transport Types:Group Translocation

• Solute can transport against concentration gradient.

• Solute is modified during transport and energy released.

• Often a high energy P-group gets translocated in a cascading sequence toward a lower energy state.

• e.g. phosphoenolpyruvate (PEP): sugar phosphotransferase system (PTS).

• PST is involved in chemotaxis.

“Send out the scavengers!”Siderophores

• Iron bioavailability is low; “rust never sleeps”.

• Bacteria release these scavenger molecules to facilitate iron transport.

• Multiple siderophores complex an iron molecule.

• Siderophores can be species specific.