Abstract
A variety of microbes can inhabit in extreme conditions. Extreme is a relative term which is viewed compared to what is normal for human beings. These microorganisms are known as oligotrophs. This work aimed to benefit from such organisms isolated from poor soils prevailing in fayoum Governorate. A survey of these organisms (specially) olignitrotrophs and oligocarbotrophs) was made on different soil samples. One hundred and twelve isolates were obtained from eight different soil sites. Ninety eight were obtained from NB/1000 (NB= nutrient broth) and fourteen from NB/10000 dilution. Fixed counts of the different isolates, when inoculated in NB medium with its different dilutions, were almost of constant counts for 30 days incubation at 30°C proved to be facultative not obligate oligotrophs. Eleven isolates produce IAA in amounts averaged 15 µg/ml and the rest were below 15 µg/ml. Five isolates only were capable to produce salyselic acids (S.A.) in appreciable amounts (< 100 µg/ml) and the rest was below 100 µg/ml. fifty four isolates solubilized zink (< 10 mm clear zone), and the rest was below 5 mm halo zone. Nine isolates solubilize phosphate (10mm clear zone) and the rest was below 5mm diameter. Fourty-seven isolates were able to fix nitrogen (olignitrotrophic) in medium deprived completely of N-source. Seventeen isolates were G- and the rest was G+. All isolates were oxidase and catalase positive but cannot ferment lactose. Most isolates were motile (95.5%), spore formers (76.6%) and all were short or long rods. Cellulase enzyme produced by seventeen and chitinase by five isolates only. All isolates examined were facultative oligotrophs as they grew on silica gel NB medium deprived of any source of carbon as well as on complete NB medium.
Highlights
Moderate environments are important to sustain normal microbial life
A variety of microbes survive and grow in such environments, and are known as extremophiles, tolerate specific extreme conditions, but usually require these for survival and growth. Many of these bacteria can be defined as obligate oligotrophs because they are unable to grow in carbon
The oligotrophic bacterial counts were found by Hashimoto et al, [3], when enumerated by a 100-fold dilution of NB, was two to three order of magnitude greater than NB-medium
Summary
Moderate environments are important to sustain normal microbial life. Moderate means environments with pH near neutral, temperature around 28-30°C, appropriate amounts of carbon, nitrogen and other nutrients, available water, aeriation ... etc. A large number of microorganisms live and survive with difficulty in soil because of the non availability and low rate of nutrients supply. A variety of microbes survive and grow in such environments, and are known as extremophiles, tolerate specific extreme conditions, but usually require these for survival and growth Many of these bacteria can be defined as obligate oligotrophs because they are unable to grow in carbon
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