Phylogenetic Diversity of Culturable Bacteria Isolated from Sediments of Passu Glacier, Pakistan

Abstract

Low temperature is very common among extreme environments on the earth. The culturable microbial diversity in soil sediment of Passu glacier, Karakoram Range, Pakistan, was investigated by 16S rRNA dependent molecular phylogeny. Ten different psychrophilic and psychrotrophic microorganisms were isolated. These microorganisms were categorized on the basis of phylogenetic analysis, physiological diversity, metabolic acti viti es and optimum temperature required for growth. The isolates we re sequenced and the results revea led that Gram-negati ve bacteria were the dominant group, whil e Gram positive rods were also found. All the Gram negative iso lates were Proteobacteria (06 isolates) whil e Firmi cutes (02 isolates) and Actinobacteri a (02 iso lates) we re the dominant Gram positives. They were identified as Acinetobac/er sp., Rhizobium sp. , Bacillus horikoshii, Brevundimonas sp. , Arthrobacter sp. , Acidovorax sp., Rhodococcus sp., and Bacillus psychrodurans. All 16S rRNA sequences were similar to previously determined sequences, with 99% identical val ues. Most of the isolates grew optimally at soc. However, they also exhibited growth at 2S and 30°C, indicating a wide growth temperature range. Effec t of limited conditions on isolates through degradation of long chain hydrocarbon (Hexadecane) was also studied. Strains Acinetobacter sp. PAS-OI , Ar/hrobac/er sp. PAS-OS, Acinetobacter sp. PAS-06, Rhodococcus sp. PAS-09 and Bacillus psychrodurans PAS-IO demonstrated maximum growth, with Rhodococcus sp. PAS-09 being the most efficient one. Effect of salinity on growth of isolates at two different temperatures was also demonstrated. Different NaCI concentrations were used ranging from I % to 8% (w/v). Bacillus horikoshii PAS-03 demonstrated maximum growth at higher concentration of NaCI (4%). Also with increase in temperature sa lt tolerance for many isolates also increased. Physiological and functiona l di versity related to sulfate and nitrate reduction under aerobic conditions revealed that five strains Rhizobium sp. P AS-02, Bacillus horikoshii PAS-03 , Arthrobacter sp. PAS-OS, Rhodococcus sp. PAS-09 and Bacillus psychrodurans PAS-l 0 were strict aerobes. Strains A cine/obacter sp. P AS-I , Brevundimonas sp. PAS-04, Acinetobacter sp. PAS-06, Acidovorax sp. PAS-07 and Acidovorax sp. PAS-08 also illustrated growth in the presence of alternate electron acceptor, like sulfate or nitrate.