The correct answer is option (D) (i) 11 and (ii) 8.6.

YATP Concept

Molar growth yield, denoted as YATP, measures grams of biomass produced per mole of ATP generated during microbial growth under energy-limited conditions. The formula is YATP = biomass (g) / ATP moles from 1 mole glucose.

Fermentation Pathways

Streptococcus faecalis uses the Embden-Meyerhof-Parnas (EMP) pathway anaerobically, yielding a net 2 ATP per glucose via homolactic fermentation to lactate. Zymomonas mobilis employs the Entner-Doudoroff (ED) pathway, producing a net 1 ATP per glucose during ethanol fermentation.

Calculations

For S. faecalis: 22 g biomass / 2 mol ATP = 11 g/mol ATP. For Z. mobilis: 8.6 g biomass / 1 mol ATP = 8.6 g/mol ATP.

Option Analysis

  • (A) (i) 11 and (ii) 4.3: Correct for S. faecalis but halves Z. mobilis yield incorrectly, ignoring its 1 ATP.
  • (B) (i) 22 and (ii) 4.3: Wrong for S. faecalis (ignores division by 2 ATP); incorrect for Z. mobilis.
  • (C) (i) 22 and (ii) 8.6: Fails to divide S. faecalis by 2 ATP; correct only for Z. mobilis.
  • (D) (i) 11 and (ii) 8.6: Matches both calculations precisely.

In the world of microbial physiology, understanding YATP molar growth yield under anaerobic fermentative growth conditions is crucial for CSIR NET aspirants tackling questions on Streptococcus faecalis and Zymomonas mobilis. One mole of glucose yields 22 grams of S. faecalis biomass or 8.6 grams of Z. mobilis—revealing key differences in ATP efficiency and biomass production.

Why ATP Yields Differ in Fermentation

S. faecalis follows the EMP pathway, netting 2 ATP per glucose through glycolysis to lactate, enabling higher biomass (22 g). Z. mobilis, via the ED pathway, nets just 1 ATP, directing more carbon to ethanol and yielding less biomass (8.6 g). This ATP disparity directly impacts YATP values.

  • EMP (S. faecalis): Glucose → 2 pyruvate + 2 ATP (net) → lactate.
  • ED (Z. mobilis): Glucose → pyruvate + 1 ATP (net) + NADPH → ethanol + CO₂.

Step-by-Step YATP Solution

Compute YATP = grams biomass / mol ATP/glucose:

S. faecalis: 22 / 2 = 11 g/mol ATP.

Z. mobilis: 8.6 / 1 = 8.6 g/mol ATP.

This confirms option (D), highlighting pathway efficiency in anaerobic fermentation.

Exam Insights for CSIR NET

Such problems test bioenergetics: EMP doubles ATP over ED, boosting yield. Standard YATP hovers ~10-12 g/mol, aligning here despite Z. mobilis’ lower value due to rapid flux. Master this for microbial growth kinetics questions.

Keywords: YATP, Streptococcus faecalis, Zymomonas mobilis, anaerobic fermentative growth, molar growth yield, glucose yield.