CHAPTER VI. 



LEUCO-THIOBACTERIA (COLOURLESS SULPHUR 

 BACTERIA). 



Family i. Beggiatoacecs. Genus i. Beggiatoa ; Genus 2. Thiothrix ; 

 Genus 3. Thioploca. 



The Leuco-Thiohacteria. — This group includes all the 

 colourless sulphur bacteria. 



Family i. Beggiatoace^. 



Straight filaments sometimes spiral or rounded. The fila- 

 ments are unicellular, and either homogeneous or divided into 

 sections by the formation of thin transverse bands of hyaline 

 slime at more or less regular intervals. Slime is formed outside 

 the membrane. In Beggiatoa slime formation is scanty ; in 

 Thiothrix the slime hardens and forms a cylindrical sheath 

 with transverse bands ; in Thioploca numerous filaments are 

 enclosed in a well-developed mass of slime. 



The filaments are motile, the degree of motility being 

 determined chiefly by the amount of slime formation. 



Reproduction is by fission, and in one genus (Beggiatoa) 

 also probably by asexual spores. 



Genera — 



1. Beggiatoa. 



2. Thiothrix. 



3. Thioploca. 



Genus I. Beggiatoa (Trevisan), 1842. 



Colourless threads, non-septate, and typically motile. 

 One species {B. alba) shows high degree of pleomorphism. 

 The varieties of form include filaments, large and small cocci, 

 short rods, and ovoid structures. These may be motile or 



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