Facultative Psychrophiles Research Articles

Studies on Antibiotics Produced by Psychrophilic Microorganisms

A screening for antibacterial antibiotics was carried out with psychrophilic microorganisms. The most active microorganism, a soil actinomycete, was selected and characterized to be a facultative psychrophile, Streptomyces sp. No. 81. This strain was found to produce antibiotic(s) in the culture fluid only at low temperature cultivation below 20°C but not at moderate temperature. Mycelial growth at low temperature seemed to be indispensable for the antibiotic production. The antibiotic produced by Streptomyces sp. No. 81 was isolated and characterized. It appeared that the antibiotic had the selective toxicity against several Gram-positive bacteria. From the comparative studies with several known antibiotics, the antibiotic appears to be a new compound derived from the new metabolic routes involving temperature-sensitive mechanisms.

THE EFFECTIVENESS OF EDTA AS A FISH PRESERVATIVE

Summary A concentration of 0.005% Na4EDTA markedly inhibited the growth of the facultative psychrophiles P. putrefaciens, P. Fragi and P. fluorescens in half strength nutrient broth at pH 7.0. Achromobacter lipolyticum was the only psychrophilic organism of 20 tested which was found to be insensitive to EDTA. The application of a 1.0% dip of Na4EDTA to haddock fillets for 1 min failed to suppress the increase in bacterial numbers on fillets stored at 3 C when compared to untreated control fillets. Refrigerated storage at 3 C was, however, extended by the dip from 5 to 9–10 days based on odor and taste evaluations. The formation of trimethylamine and volatile basic nitrogen was markedly suppressed in EDTA dipped fillets.

Seasonal selection of estuarine bacteria by water temperature

A series of observations on heterotrophic bacteria planktonic in a temperate estuary, Narragansett Bay, Rhode Island, have been made to determine whether seasonal changes in water temperature are sufficient to select thermal and taxonomic types. Semi-monthly samples obtained for two one-year periods and one half-year period were examined for changes in bacterial populations. More than 2500 isolates were determined as to genus and some six hundred representative isolates were examined simultaneously for their growth-temperature spectra at 20 temperatures 2°C apart. The growth range of natural bacterial populations varied with water temperature, but lagged two months out of phase. This seasonal shift in temperature range for growth gave opposing indications of population changes with only small differences in incubation temperatures. All thermal types detected could be isolated and their population trends observed by reincubating pretempered plates at 0, 18, and 36°C after surface-inoculation. Mesophilic isolates (growth above 10°C and optimum above 30°C) were only obtained on the 36°C plates when the water temperature was above 10°C. A number of these isolates were cold sensitive and labile below 18°C. Obligate psychrophiles (growth below 16–20°C, 9–10°C optimum) were only obtained on 0°C plates when water temperatures were below 10°C. Two additional thermal types were obtained on both the 0°C and 18°C plates. Organisms which grew at 0°C and had a broad optimum growth range between 10°C and 30°C were considered to be facultative psychrophiles while organisms which also grew at 0°C, but had a narrower optimal peak around 18–20°C were considered psychrotolerant. In addition to these main thermal types, a few isolates of several taxonomic groups exhibited a tendency for multiple temperature optima. The seasonal selection of thermal types by water temperature occurred in all taxonomic groupings. There was no apparent suppression or enhancement of any taxonomic group due to temperature.

THE MULTIPLICATION OF COLI‐AEROGENES BACTERIA IN MILK STORED AT 3–5°

SUMMARY: When 108 samples of individual farm milk supplies were held at 3—5° for 72 hr, 35·2% showed increases in coli‐aerogenes organisms of over one‐hundredfold and 10·2% increases of more than one‐thousandfold. The coli‐aerogenes microflora after refrigeration was dominated by Klebsiella cloacae and K. aerogenes I. While some strains of all the coli‐aerogenes types isolated showed growth, though sometimes scanty, on yeast‐dextrose agar in 5 days at 3—5°, the majority of the strains of K. cloacae showed luxuriant growth under these conditions and can be considered as typical facultative psychrophiles of milk.