Some of the blue-green bacteria are 

 especially significant to the function of 

 the marsh since the heterocystous, 

 filamentous blue-greens are responsible 

 for nitrogen fixation on the marsh 

 surface. In Massachusetts, where algal 

 mats dominate the marsh surface, Calothryx 

 is the important genus. Under the grass, 

 Stigonema is responsible for most of the 

 nitrogen fixation (Van Raalte et al. 

 1976). 



3.3 BACTERIA AND FUNGI 



An abundance of bacteria function in 

 the anoxic muds and play a very important 

 role in the salt marsh. They are respon- 

 sible for processes varying from photosyn- 

 thesis to various aspects of decomposi- 

 tion. Fungi are also active in decomposi- 

 tion though their ecology is much less 

 well understood. Because fungi are aero- 

 bic organisms, their activities are lim- 

 ited to the surface layers of the marsh. 



A number of kinds of bacteria are 

 abundant enough in salt marshes to be 

 visible to the naked eye en masse . For 

 example, the red photosynthetic sulfur 

 bacteria form layers just under the 

 surface where they are protected from 

 oxygen, which poisons them, but where they 

 still get enough light to photosynthesize. 

 Their red pigments are often visible on 

 the surface of sand layers, but they are 

 also present and visible with careful 

 examination in muddy areas. These 

 organisms photosynthesize using H 2 S as a 

 source of hydrogen for reducing power. 

 They produce sulfur as a byproduct. 

 (Green plants use H 2 and produce oxygen.) 

 The sulfur oxidizers are often seen as a 

 white layer on the marsh surface. The 

 sulfur granules resulting from the 

 oxidation of H 2 S are stored within the 

 cells and enable us to see the microbes. 



Beggiatoa is a common genus that 

 derives energy from oxidizing reduced 

 sulfur. Bacteria that reduce sulfate are 

 common in salt marshes and are 

 occasionally noticed because of the smell 

 of the H 2 S they produce. These are not 

 visible except for the general black color 

 of the marsh sediments to which they 

 contribute. Bacteria that oxidize sulfide 

 or use it as a hydrogen source depend on 



the reducers for their source of raw 

 material s. 



P i c h i a spartinae , a yeast, is 

 reported to be an abundant organism in the 

 microflora of Louisiana salt marshes 

 (Meyers et al. 1975). It is extremely 

 common on the surface of, and in fluid- 

 filled cavities within stems of, S. 

 alterni flora . It can survive on Spartina 

 lipids and has an active B-gl ucosidase 

 system (for hydrolysis of sugars derived 

 from cellulose). It probably makes im- 

 portant contributions to marsh decomposi- 

 tion processes once the cellulose has been 

 initially attacked (a process in which 

 other fungi are active). 



Pichia spartinae and another yeast 

 ( Kluyveromyces drosophilarum ) made up 

 over 70% of salt marsh yeasts found by 

 Meyers et al. (1973) in undisturbed 

 Louisiana marshes. Pichia ohmeri became 

 one of the most abundant yeasts in a 

 Louisiana salt marsh as the result of 

 controlled additions of oil (Meyers et al . 

 1973). 



Species of the yeast Candida are 

 significant contributors to oil 

 degradation in east coast salt marshes. 

 Claviceps purpurea , the ergot fungus, 

 infects Spartina seeds throughout the 

 Atlantic and gulf coasts (Eleuterius and 

 Meyers 1974). Ergot, which is responsible 

 for poisoning of rye flour, is widely 

 distributed in salt marshes, but may be of 

 little ecological significance there. 

 Though marsh fungi are important in the 

 formation of detritus from Spartina (J. 

 Hobbie, Marine Biological Laboratory, 

 unpubl. data), they need more study. 



In this report, most of the important 

 microbes in the marsh system are 

 identified by their functions. To a 

 considerable extent this has been done 

 even by microbiologists in the past. It 

 is now known that even some of the 

 apparently compact groups are really 

 microbes of widely differing ancestry. 

 Some of these groups are responsible for 

 denitrif ication, nitrification, nitrogen 

 fixation, and methane production. The 

 largest functional group, "decomposers," 

 is even less unified for it includes most 

 non-photosynthetic and chemosynthetic 

 microbes. 



16 



