THE 
HEW PHYTOIiOGIST. 
Vol. XIII, Nos. i & 2. Jan. & Feb., 1914. 
[Published February 25th, 1914.] 
A CONTRIBUTION TO THE PHYSIOLOGY OF THE 
PURPLE SULPHUR BACTERIA. 
By Macgregor Skene, B.Sc., 
Lecturer on Vegetable Physiology , Aberdeen University. 
U NDER the name “Sulphur Bacteria” we include a number 
of forms which in appearance and in mode of life stand far 
apart. They have one characteristic in common : all are capable 
of oxidising sulphur or one of its unoxidised compounds, producing 
in some cases sulphur, in others sulphuric acid. Two series may 
be distinguished. To the first belong those forms which are 
morphologically similar to ordinary bacteria, and which do not store 
up sulphur internally. Such are the Thiobacilli which have been 
described by Nathansohn (1902) Beijerinck (1904) and Lieske (1912 a 
and b). They oxidise thiosulphates to sulphur or sulphuric acid, and so 
obtain energy which they expend on the reduction of carbon dioxide, 
by this means gaining the possibility of leading an autotrophic life. 
The second series includes a number of forms which exhibit remark¬ 
able morphological peculiarities. They oxidise hydrogen sulphide 
to sulphuric acid—a process which takes place in two stages: 
sulphur is first formed, and is stored inside the cells in large 
globules, which are then further oxidised. This storage of sulphur 
lends the bacteria a very characteristic appearance. Moreover 
most of the organisms in question are very large, and live united in 
colonies or in filaments. 
Here we can distinguish two sub-classes. The first consists of 
colourless forms. Of these two— Beggiatoa and Thiothrix —have 
been investigated quite recently from the physiological standpoint 
by Keil (1912); both have proved to be autotrophic. Finally we 
