Indonesia has many fermented beverages, and yeast become one of the agents in fermented process. Yeasts has a role to transform carbohydrate complex into simple compounds with release secondary metabolism to environment like amylase enzyme. This study aims to get the isolate of yeast that can potentially produce amylase enzyme. This research conducted in October 2018 until March 2019 in Microbiology Laboratory of Universitas Negeri Jakarta. The screening test of potential isolate producing amylase enzyme was performed on yeast isolate from eight source of indigenous fermented beverages that can grow in YMA medium with pH 2. Screening was carried out on YPSA medium with diffusion agar method. From 50 Isolates, 16 isolates with the codes IB4, IB15, IB20, IB21, IB26, IB36, IL78, IL80, IL81, IL86, IL88, IL97, IL113, IL136, IL146, and IL150, were able to form clear zone after 1-day incubation in room temperature. The highest amylolytic index was produced by IL86 (1,019 mm). Forming the clear zone is proof that yeast can transform starch become simpler sugar like maltose as iodine-starch reaction is resulting amylose helix and iodine become I3 − that filled main core helix. In addition to this, iodine forms complexes with starch molecules showed a dark purple colour.

Background: Apples often experience postharvest damage due to being attacked by mold organisms. Several groups of molds such as Aspergillus sp., Penicilium expansum, Botrytis cinerea, and Venturia sp. can cause a serious postharvest disease exhibited as watery regions where areas of blue-green tufts of spores develop. Current methods using fungicides to control pathogenic fungi can cause resistance if applied in long term. An alternative procedure using yeast as a biological agent has been found. Objective: The aim of this study is to screen potential yeast which has ability to inhibit the growth of Aspergillus brasielensis (isolate A1) and Aspergillus flavus section flavi (isolate A17) isolated from apple fruits. Methods: Antagonism test using YMA dual culture medium using in vitro assays and ITS rDNA identification were performed. Results: The result showed that 3 out of 19 yeast isolated from Cerbera manghas L, T1, T3 and T4, demonstrated the potential ability as biocontrol agent. ITS rDNA identification demonstrated that T1 has similarity to Rhodotorula mucilaginosa while T3 and T4 were identified as Aureobasidium sp. nov.. The 3 isolates exhibited the ability to reduce the growth of A. brasiliensis sensu lato better than dithane 0.3% with a disease incidence (DI) of 100% and a disease severity (DS) value of 45%. Only isolate T1 and T3 were able to reduce decay symptoms in apples inoculated with A. flavus sensu lato (with DO and DS were 100% and 25%, respectively) compared to dithane pesticides 0.3%. Conclusion: This study indicated that competition between nutrients occurs between pathogenic molds and under-yeast in vitro and in vivo conditions. However, further studies in the future might be able to elucidate the 'killer' activity and interaction with the pathogen cells and the bio-product production using Rhodotorula mucilaginosa and Aureoubasidium namibiae strains to control postharvest diseases.

The aim of this research is to find the isolates of yeast that have the ability to produce enzyme amylase. The strains that can produce the amylase enzyme are characterized by a clear zone around colonies after addition of iodine solution in medium containing 1% starch soluble. Activity of amylase enzyme can be determined by measuring using spectrophotometer at λ 540 nm. The isolation result obtained 75 representative yeast isolates with colony color white butyrous 16%, white mucoid 29.3%, yellowish white 18.7%, cream 20%, peach mucoid 9.3%, and orange mucoid 6,7%. Screening results showed that 8 isolates were able to produce an amylase enzyme with code isolates K33, K34, K36, K37, K48, K107, and K128. A total of two potential yeast isolates in yielding amylase with K34 and K39 isolate codes had amylolytic index 2.89 and 2.27. The highest enzyme activity was produced by K48 (0.88 U/mL).

Pyrene degradation and biosurfactant activity by a new strain identified as Gordonia cholesterolivorans AMP 10 were studied. The strain grew well and produced effective biosurfactants in the presence of glucose, sucrose, and crude oil. The biosurfactants production was detected by the decreased surface tension of the medium and emulsification activity. Analysis of microbial growth parameters showed that AMP10 grew best at 50 µg mL -1 pyrene concentration, leading to 96 % degradation of pyrene within 7 days. The result of nested PCR analysis revealed that this isolate possessed the nahAc gene which encodes dioxygenase enzyme for initial degradation of Polycyclic Aromatic Hydrocarbon (PAH). Observation of both tensio-active and emulsifying activities indicated that biosurfactants which produced by AMP 10 when grown on glucose could lower the surface tension of medium from 71.3 mN/m to 24.7 mN/m and formed a stable emulsion in used lubricant oil with an emulsification index (E24) of 74%. According to the results, it is suggested that the bacterial isolates G. cholesterolivorans AMP10 are suitable candidates for bioremediation of PAH-contaminated environments.

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