Abstract
Afifella marina strain ME (KC205142), a purple non-sulfur bacterium was isolated from mangrove habitats of Sabah. The effects of light intensities and photoperiods on proteolytic activity in Afifella marina strain ME (KC205142) were investigated. Secretion of proteolytic enzymes in Afifella marina was preliminarily assessed by skim milk agarose media. Subsequently, light intensities, such as, dark, 1000, 1500, 2000, 2500, 3000, 3500, 4000, 4500 and 5000 lux were used to evaluate the effects on proteolytic activity in Afifella marina strain ME under anaerobic condition. After that, the effect of photoperiods on proteolytic activity was monitored under anaerobic light condition (3000 lux) at 0 h (0L/24D), 6 h (6L/18D), 12 h (12L/12D), 18 h (18L/6D) and 24 h (24L/0D) of photoperiod. The highest proteolytic activity of 74.67 U was recorded at 3000 lux illumination light intensity. The proteolytic activity in bacterium Afifella marina strain ME was positively associated with the dry cell weight. The proteolytic activity of 72.67 U in bacterium Afifella marina strain ME at 18 h (18L/6D) photoperiod is not significantly different (p > 0.05) from proteolytic activity of 74.67 U recorded at continuous light (24L/0D) condition. Light intensity of 3000 lux, culture period of 48 h and a photoperiod of 18 h (18L/ 6D) were the optimum parameters for proteolytic activity in bacterium Afifella marina strain ME.
Highlights
Purple non-sulfur bacteria (PNSB) are anoxygenic photosynthetic bacteria that prefer to live as photoheterotrophs
The proteolytic activity of 72.67 U in bacterium Afifella marina strain ME at 18 h (18L/6D) photoperiod is not significantly different (p > 0.05) from proteolytic activity of 74.67 U recorded at continuous light (24L/0D) condition
Similar observations were reported in other studies where purple non-sulfur bacteria such as Rhodopseudomonas palustris grown in Malate basal medium at 28 ̊C [22] and Rubrivivax gelatinosus KDDS1 grown in Glutamate-malate (GM) medium under anaerobic light conditions at light intensity of 3000 lux and a temperature of 35 ̊C for 48 h [13] exhibited proteolytic activity
Summary
Purple non-sulfur bacteria (PNSB) are anoxygenic photosynthetic bacteria that prefer to live as photoheterotrophs. These groups of bacteria inhabit in a wide range of natural environments such as sediments [1], coastal seawaters [2], brackish water [3], mud from the bottom of tidal pool [3] and lakes [4]. PNSB are known to produce extracellular enzymes such as proteases, lipases, esterase and alkaline phosphatase [12]. Purple non-sulfur bacterium, Rubrivivax gelatinosus grown in GM media under anaerobic light condition for 48 h has been reported to produce significant level of proteolytic activity [13]. The extracellular enzymes contributed to the nutrition of the bacterium by hydrolyzing large molecular organic compounds to smaller oligomers and monomeric components which can directly be absorbed by the cells [14]
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