When sodium chloride crystallizes in an evaporitic environment, living halobacteria are entrapped within the fluid inclusions which form as the crystals develop. Trapped cells have been observed in natural salts from a marine saltern and from Lake Magadi. Entrapment occurs under both neutral and alkaline conditions. Salt crystals have been grown under controlled conditions from solutions containing pure culture suspensions of halobacteria at densities comparable to those reported from natural evaporitic habitats. Crystals formed in solutions heavily loaded with bacterial cells contained more and larger inclusions than crystals formed from sterile solutions, and thus bacterial entrapment may affect the physical characteristics of the product. Representative strains of each major grouping within the Halobacteriaceae except the genus Halococcus exhibited entrapment and survival within salt crystals. Continued motility has been demonstrated for up to three weeks after entrapment. All strains tested to date retained viability for a minimum of six months. Non-motile and non-viable cells were also entrapped. I N T R O D U C T I O NThe questions raised by the survival of 'red bacteria' in salt brines and on solar salt used for preserving fish, meat and hides have been of both historical and practical interest (BaasBecking, 1931). Harrison & Kennedy (1922) demonstrated that the red discoloration of salted fish was due to the fact that red halobacteria remain viable in crude solar salt for periods of months after the salt has been harvested. Dussault (1958) established that bacterial survival in crude solar salt over periods of 20-60 d was improved by storage in warm, humid conditions, with salt samples even showing some increase in numbers under the most favourable storage conditions. The duration of survival has remained largely unsurveyed, although Bain et al. (1958) were able to recover viable 'pink bacteria' from solar salt samples that had been in storage for four years. The literature has tended to be non-specific about the actual relationship of the attendant bacterial flora to the crystalline salt. Some authors have employed the descriptive term 'contamination', thereby suggesting, perhaps unintentionally, a largely accidental and superficial relationship. The work reported here was undertaken in an effort to increase understanding of this relationship.A key to understanding halobacterial survival in salt is found by examining the mineralogy of the host substance. Naturally deposited crystalline sodium chloride (halite) is a cubic mineral which, like many other minerals such as quartz, contains large numbers of fluid inclusions. The water content of natural rock salts, which is a significant factor in the mechanical behaviour of salt deposits (Urai et al., 1986) is usually in the range of 0-1-1-0% (w/w) (Roedder, 1984). The water content of freshly harvested solar salts is usually in the range of 2-6% (w/w), in some cases up to 15% (w/w) (Lefond, 1969). Fluid inclusions, readily observed under low power magnific...

Samples were taken from the Winsford salt mine in Cheshire, England, which exploits bedded deposits from the Triassic Period (195-225 million years ago, MYA) and from Boulby potash mine in Cleveland, England, which is Permian (225-270 MYA) and is mined for the mineral sylvite (KC1). Halobacteria and obligately halophilic eubacteria were isolated from several different sample types. The halobacteria were characterized by chemotaxonomic methods and most but not all were shown to be very similar but not identical to those halobacterial types that dominate in highly concentrated surface brines. There was a high degree of similarity between the two mine populations, but some strains were particular to each mine.

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A bacterium producing a deep blue pigment was isolated from Narragansett Bay, Rhode Island, and identified as Pseudomonas nigrifaciens. It requires at least 6.4 p.p.t. salinity for growth, 9.6 p.p.t. for pigmentation, and grows from 4 to 30 C, optimally at 15–18 C. An organic nitrogen source is necessary for growth but no specific amino acids or growth factors are required. Two major seawater ions are essential, potassium (10−3 M minimum, 8 × 10−3 M optimum) and magnesium (growth occurring in 1 week on 10−5 M, 10−2 M optimum at 20 h). Growth occurs without addition of sodium or chloride ion. Optimum pigmentation occurs on solid media, but pigmentation does occur in shaken vitamin-free casamino acids medium of 35 p.p.t. salinity. Water-soluble blue pigment appears during log phase and breaks down to a brownish coloration during stationary phase, coinciding with a pH change from 7.4 to 8.3. The blue pigment in sterile filtered culture fluid exhibits redox and pH indicator properties. Redox activity is observed in culture fluid, where standing causes reduction and shaking reoxidation.

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