Definition check – autotrophic bacteria Autotrophic bacteria are those which:

Introduction / Context:
Autotrophy is a core metabolic strategy in which organisms synthesize organic biomass from inorganic carbon (CO₂). In bacteria, this can be coupled to light (photoautotrophy) or to oxidation of reduced inorganic compounds (chemolithoautotrophy). The question asks for the accurate definition of autotrophic bacteria.

Given Data / Assumptions:

• Autotrophs rely on CO₂ as principal carbon source.
• Energy can come from light or chemical oxidation.
• Other listed statements refer to unrelated traits (capsules, pigments, drug susceptibility, oxygen requirement).

Concept / Approach:
The hallmark of autotrophy is CO₂ fixation into organic molecules via pathways such as the Calvin cycle or reverse TCA, powered by photonic or chemical energy. This distinguishes autotrophs from heterotrophs, which must assimilate preformed organic carbon. Many ecologically important bacteria, including nitrifiers and sulfur oxidizers, are autotrophs.

Step-by-Step Solution:
Identify defining feature: CO₂ as carbon source.Include energy source note: light or inorganic chemicals.Select the option that explicitly states CO₂ fixation as “making their own food.”

Verification / Alternative check:
Textbook definitions (microbial physiology) consistently define autotrophs by their carbon source, not by morphology, pigmentation, or antibiotic response.

Why Other Options Are Wrong:

• Glycocalyx formation: relates to surface structures and biofilms, not carbon metabolism.
• Penicillin susceptibility: depends on cell wall traits; not a defining metabolic feature.
• Blue–green pigment: describes some cyanobacteria but is not a defining property of autotrophy.
• Oxygen absence: conflates metabolism with aerotolerance; many autotrophs are aerobic.

Common Pitfalls:
Equating autotrophy with photosynthesis only; chemolithoautotrophs also fix CO₂ without light.

Final Answer:
Make their own food by fixing inorganic carbon (CO₂) using an energy source.