ATTACHMENT OF MARINE BACTERIA TO ZOOPLANKTON 



by 

 Galen E. Jones 



The abundance of marine bacteria living free in 

 the open sea is low (ZoBell, 191*6) . The reasons 

 for the small numbers of microorganisms in the 

 sea have been considered by various workers as 

 summarized by Orlob (1956). Dilute amounts of 

 organic matter on solid surfaces cause marine 

 bacteria to concentrate on these surfaces (Stark 

 et al., 1938; Heukelekian and Heller, 191*0). 

 In addition, many marine bacteria demonstrate 

 definite attachment propensities (ZoBell, 191*6) . 

 If marine bacteria attach to the surface of liv- 

 ing organisms there is the opportunity for a 

 symbiosis between the bacteria and the phytop- 

 lankton or zooplankton whereby the metabolic 

 products from both groups might benefit each 

 other 5 commensalism whereby one of the members 

 of the association is benefited; or antagonism 

 where one or both members may be inhibited by 

 the products of the other. 



This investigation was conducted to obtain informa- 

 tion concerning the numbers of bacteria attached 

 to plankton as opposed to those living free in 

 the water. 



METHODS 



A -meter-net tow was taken at a depth of 20 m. 

 with a new, clean net at 08°55' N latitude, 

 88°1*7' W longitude. One species of zooplank- 

 ton predominated: the red radiolarian, 

 Castanidium cf . longispinum Haecker. Few 

 other zooplankters existed in this sample. 

 Immediately after the net was pulled aboard, about 

 one g.wet weight of these packed radiolarians 

 was transferred to a prescription bottle contain- 

 ing 1*5 ml. of sea water. Another sample of the 

 radiolarians was transferred to a bottle con- 

 taining 10 ppm. of the surface active agent, 

 Tween 80, In 1*5 ml. of sea water. Tween 80, a 

 relatively nontoxic surface active agent for 

 marine bacteria (Jones, 1957) was used in an 

 effort to remove bacteria from the plankton. 

 It was estimated that the wet weight of the scoop 

 of radiolarians placed in the Tween 80 was about 

 two-thirds of that in the sterile sea water. 

 Both of these samples were diluted l/lOO with 

 sterile sea water. These samples were shaken 

 vigorously for one minute. 



RESULTS 



Inocula were taken from l/lOO dilution as 

 follows: 0.1, 0.5 and 1.0 ml. These were 

 plated by the pour-plate technique into a 

 peptone-yeast extract medium (Oppenheimer 

 and ZoBell, 1952). The plates were Incubated 

 for 11 days at 29-31°C. The results appear 

 in Table 7. 



Little quantitative information can be 

 derived from this particular experiment 

 since the inoculum was not weighed and the 

 amounts of plankton in the bottles were not 

 estimated as equal. If the estimate of two- 

 thirds as many radiolarians in the bottle 

 shaken with 10 ppm. Tween 80 can be assumed 

 correct, the Tween 80 had little effect on 

 dislodging additional bacteria from the zoo- 

 plankters. However, the number of bacteria 

 associated with the radiolarians was certainly 

 considerably higher than exist free in the 

 water as estimated by other bacterial counts 

 recorded in this cruise. It can be assumed 

 from this experiment that there are between 

 50,000 and 100,000 bacteria per gram of wet 

 radiolarians which is about 10-^more bacteria 

 than are generally present in sea water. 



This experiment should be taken only as in- 

 dicative of attachment of bacteria to 

 marine plankton since only one group of 

 organisms, was tested because the actual 

 numbers of bacteria free in the water was 

 not measured at the same place and time. 

 However, the order of magnitude of bacteria 

 found associated with the radiolarian, 

 Castanidium cf . longispinum Haecker , when 

 compared with the bacteria generally found 

 in similar waters strongly suggests intimate 

 association. 



ACKNOWLEDGEMENT 



The author would like to thank Mr. William 

 R. Riedel, Scripps Institution of Oceano- 

 graphy, for his identification of the radio- 

 larian, Castanidium cf . longispinum Haecker. 



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