Structure and Reproduction
Bacteria are unicellular organisms although some of them form chains or groups of cells. Morphologically there are the following three forms:
In their structure and activities they form a rather well-defined group of organisms, although some possess animal characteristics, especially in chemical composition, while others approach more nearly the plants, particularly the blue-green algae, with which they share the characteristic of having scattered nuclear material. Some authors consider them as occupying an intermediate position between the plants and animals (Jordan, 1931). A distinct plant characteristic is the ability of some to synthesize such complex substances as amino acids with only ammonia as a source of nitrogen. It is important to note that none possess chlorophyll, nor are their cell walls composed of cellulose. For convenience, however, they are all placed with the plants; but owing to the absence of chlorophyll in their structure they must be regarded as fungi, and since their common method of multiplication is by simple fission, they are named fission fungi or Schizomycetes.
Structurally, the marine bacteria are represented mostly by motile rods and various types of vibrios or comma-shaped forms, and there are fewer spore-formers in the sea than on land (Waksman, 1934). About 70 per cent of marine bacteria are colored as opposed to 15 per cent of the terrestrial forms.
Characteristically, bacteria are the smallest of all organisms, some measuring only 0.0005 mm in diameter. This extreme minuteness has a profound bearing on the activities of bacteria and also introduces very special problems and difficulties in the technique of collecting and in the estimation of actual numbers and mass.
Characteristic also of bacteria is their rapid rate of reproduction. This is accomplished by vegetative cell division. It may again be emphasized here that in nearly all instances where swarms of organisms—bacteria, diatoms, dinoflagellates—occur in such large numbers that the water is discolored by the accumulation of their bodies, the method of reproduction has been one of binary fission. Assuming an uninterrupted physiological state and optimum growing conditions, the accumulation of individuals can be extremely rapid since the increase is by geometric progression. The rate of division of bacteria may be as frequent as once every twenty or thirty minutes. Hence, biologically, there is a tremendous potentiality to build up an excessively large mass. However, large masses do not accumulate because of natural checks which hold the tendency to mass production within bounds. Among such checks may be mentioned availability of food supply, formation of toxic metabolic products, physical-chemical conditions of the water, nature of substratum, and consumption by other organisms. An understanding of these checks or controlling factors is one of the ends sought in the study of marine bacteriology, for such an understanding provides an explanation
Associated with bacterial reproduction is the faculty of spore formation, whereby the individual bacterium of certain species is enabled to withstand adverse conditions while remaining in a state of quiescence for long periods of time. How significant this faculty is in the marine environment, where physical and chemical conditions are relatively uniform, at least with respect to the open water, is not clear. Viable bacteria have been taken from strata of marine mud where they must have remained buried for thousands of years (p. 920). However, the functions of these buried forms as effective transformers in the water or immediate bottom have apparently ceased, and the likelihood of their revival in the sea bottom is remote. Those not too deeply buried may serve to some extent as food for burrowing detritus-feeding animals.