84 GENERAL SYSTEMATIC BACTERIOLOGY 



Key to the Genera of Mycobacterieae 

 One genus only, Mycobacterium. 



Key to Genera of Spirillaceae 



A. Cells not larger at center, not tapering. 



1. Cells usually short, only a segment of a spiral. One or rarely two or three 



polar flagella Genus 1 . Vibrio 



2. Cells longer, usually with a tuft of polar flagella. 



Genus 2. Spirillum 



B. Cells enlarged at center and tapering. 



Genus 3. Paraspirillum 



Key to the Genera of Nitrobacteriaceae 



A. Cells rod shaped. 



1. Oxidizing ammonia to nitrous acid. Motile. 



Genus 1. Nitrosomonas 



2. Oxidizing nitrous acid to nitric acid. 



Genus 2. Nitrobacter 



B. Cells spherical Genus 3. Nitrosococcus 



Key to the Genera of Chlamydobacteriaceae 



1. Filaments not usually permanently attached. 



a. Filaments straight, or at least not twisted. 



Genus 1. Leptothrix 



b. Filaments twisted Genus 2. Didymohelix 



2. Filaments attached. 



a. Filaments unbranched Genus 3. Crenothrix 



b. Filaments show pseudodichotomous or false branching. 



(1) Swarm cells developed (motile conidia). Usually without a 



deposit of iron oxid in the sheath. 



Genus 4. Sphaerotilus 



(2) Spherical, non-motile conidia. Usually with iron oxide. 



Genus 5. Clonothrix 



Key to the Genera of Actinomycetaceae 



A. No evident aerial threads or conidia formed. Usually parasitic. Often 



anaerobic or microaerophilic. 



1. Threads usually not branched. 



a. Threads disjointing very readily; long mycelial threads uncommon. 



Genus 1. Actinobacillus 



b. Threads longer, not disjointing into short rods. 



Genus 2. Leptotrichia 



2. Threads more or less branched, frequently clubbed in tissues. 



Genus 3. Actinomyces 



B. Aerial threads and conidia evident on culture media. 



Genus 4. Nocardia 



