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#Firmicutes

3 public questions tagged with this topic.

Microbial Classification

Which bacteria stain Gram-negative despite being Firmicutes?

Veillonella represents anaerobic Gram-negative cocci within class Negativicutes of phylum Firmicutes exhibiting diderm envelope architecture that stains Gram-negative despite firmicute phylogenetic affiliation. Genomic analysis shows presence of outer membrane with lipopolysaccharide atypical for Gram-positives, interpreted as secondary acquisition within Firmicutes. These commensals metabolize lactate to propionate in oral cavity and gut. Exception demonstrates that Gram stain reaction does not always reflect phylogeny, challenging classical determinative criteria, as Veillonella clusters wit

Ref: Campbell Biology Chapter 27 Negativicutes Veillonella Gram-negative Firmicutes; Bergey's Manual Volume 3 Veillonella diderm exception

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Microbial Classification

Low G+C Gram-positive bacteria belong to

Low G+C Gram-positive bacteria belong to phylum Firmicutes recently renamed Bacillota, distinguished by genomic guanine-cytosine content of approximately 30 to 50 percent, lower than actinobacterial counterparts. This composition influences codon usage, thermal stability, and phylogenetic clustering via 16S rRNA secondary structure signatures. Monoderm envelope contains thick peptidoglycan with lysine-type crosslinks and teichoic acids providing structural integrity. Genera include Bacillus, Clostridium, Enterococcus, Lactobacillus, and Staphylococcus, many forming resilient endospores for sur

Ref: Bergey's Manual Volume 3 Firmicutes low GC Gram-positives; Madigan Microbiology Chapter 14 Bacillus Clostridium low GC content

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Microbial Classification

Firmicutes are characterized by

Firmicutes, now reclassified as Bacillota, represent low G+C monoderm bacteria characterized by an exceptionally thick multilayered peptidoglycan network crosslinked with peptide interbridges and anionic teichoic acids. This robust wall retains crystal violet-iodine complex during Gram staining, conferring positive reaction and protection against osmotic stress. It serves as target for lysozyme and beta-lactams. Members include Bacillus, Clostridium, Staphylococcus, and Lactobacillus, exhibiting endospore formation in some genera. Despite occasional Gram-negative staining variants, thick pepti

Ref: Bergey's Manual Systematic Bacteriology Volume 3 Firmicutes thick peptidoglycan; Prescott Microbiology 10th ed., Chapter 15 Gram-positive bacteria

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