MARINE BACTERIA AND FUNGI IN THE GULF OF MEXICO ' 



By Claude E. ZoBell, Scripps Institution of Oceanography, University of California 



Although the marine environment around the 

 West Indies was one of the first to be examined 

 by a bacteriologist (Fischer 1886) and has since 

 been quite extensively studied (Drew 1912; 

 Bavendamm 1932), there are very few published 

 reports on bacteria and fungi in the nearby Gulf 

 of Mexico. The author has been actively inter- 

 ested in the Gulf coast area since 1940, but the 

 semiconfidential nature of the research projects 

 has contraindicated the publication of the results. 

 This paper summarizes personal observations in 

 the region along with published reports that have 

 a direct bearing upon microbiological conditions 

 in the Gulf of Mexico where observations have 

 been confined almost exclusively to regions near 

 shore. The rather extensive but scattered liter- 

 ature on marine microbiology has been reviewed 

 by Issatchenko (1914), Bavendamm (1932), 

 Benecke (1933), ZoBell and Upham (1944), and 

 ZoBell (1946a, 1947). Also noteworthy is the 

 comprehensive article by Williams (1951) on the 

 occurrence, importance, and characteristics of 

 bacteria in the sea. 



Waters of the littoral zone in the Gulf of 

 Mexico are veritable bacterial gardens. At scat- 

 tered stations from Tortugas to Aransas Pass, 

 where water samples have been examined, bacterial 

 populations ranging from thousands to many 

 million per ml. have been observed. Large num- 

 bers of living bacteria have also been found in 

 bottom sediments. The methods employed by 

 various investigators for collecting and analyzing 

 samples of water and marine sediments for num- 

 bers and kinds of bacteria have been summarized 

 by ZoBell (1946a). 



The abundance of bacteria in shallow Gulf 

 waters, which greatly exceeds the abundance of 

 bacteria in the open ocean, is believed to be 

 attributable primarily to the higher content in 

 the former of organic matter and suspended solids, 



I Contribution from the Scripps Institution of Oceanography, New Series 

 No. 661. This paper is a contribution from the American Petroleum Insti- 

 tute Research Project 43A. 



both of which promote the growth of bacteria. 

 The influx of fresh water with its load of organic 

 nutrients from land drainage is also a contributing 

 factor along the littoral zone. Here there is a com- 

 mingling of both fresh-water and marine micro- 

 organisms and numerous transitional stages of 

 both kinds. The observations of Berkeley (1919), 

 Korinek (1926), Lipman (1926), Burke and Baird 

 (1931), ZoBell and Feltham (1933), Burke (1934), 

 and others indicate that ordinarily bacteria from 

 fresh-water or terrestrial sources do not survive 

 very long in sea water, but if the transition to the 

 salt-water environment is gradual, as in brackish 

 water of increasing salinity, a good many fresh- 

 water forms may become acclimated to the 

 marine environment (ZoBell and Michener 1938). 

 The bacterial flora of the Gulf coast region is 

 characterized by exceptional biochemical versa- 

 tility, cultures having been isolated that catalyze 

 the transformation of virtually all types of organic 

 matter and a good many Inorganic substances. 

 In the latter category are autotrophic bacteria of 

 various kinds that oxidize hydrogen sulfide either 

 in darkness or under the influence of sunlight 

 (van Niel 1931, 1944). Autotrophs which oxidize 

 ammonia to nitrite appear to be more common in 

 surface water and sediment than those which 

 oxidize nitrite to nitrate (Carey 1938). Methane 

 oxidizers (Hutton and ZoBell 1949) were found 

 in the topmost portions of mud samples from the 

 Gulf coast region, and sulfate-reducing bacteria 

 which oxidize molecular hydrogen as the sole 

 source of energy were found in numerous samples 

 from considerable depth (Sisler and ZoBell 1950). 

 Besides modifying inorganic substances, auto- 

 trophic bacteria are primary producers of organic 

 matter. While some obtain their energy from 

 sunlight in the manner of other photosynthetic 

 plants, most autotrophic bacteria obtain their 

 energy for the reduction of carbon dioxide from 

 the oxidation of substances such as hydrogen 

 sulfide, hydrogen, methane, ammonia, or nitrite. 



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