Studies On Mangrove Yeast Diversity And Single Cell Protein

Mangrove wetland is a unique ecosystem and is rich in bioresources．In thisarticle,the rOOtS,stems,branches,leaves,barks,fruits,and flowers from 18species of the mangrove plants,their accompanying trees,seawater andsediments in mangrove ecosystems in China were used as sources for isolation ofyeasts．A total of 270 yeast strains were obtained from the samples．The resultsof routine identification and phylogenetic analysis show that they belonged to 22genera and 45 species．Of all the 270 strains,Candida spp．was predominant withthe proportion of44．44%,followed by Kluyveromyces spp．(8．51%),Pichia spp．(7．40%),Kodamaea ohmeri(5．56%),lssatchenkia spp．(4．81%)andDebaryomyces hansenii(4．44%)．We also found that strains N02-2．3 and ST3-1Y3belonged to the undescribed species of Pichia sp．and Trichosporon sp．respectively while strain HN-12 was not related to any known yeast strains．Thismeans that different yeast strains of Candida spp．especially C tropicalis werewidely distributed in the mangrove ecosystems and may play an important rolein the mangrove ecosystems．After determination of the protein contents fromsome representatiVes of the yeast strains isolated from the mangrove ecosystemsin China,we found that Cryptococcus ureus G7a and Pichia anomala 2E00778contained 52．5%(w／w)and 44．8%(w／w)proteins in their cells,respectively．The highly thermosensitive and permeable mutants are the mutants fromwhich intracellular contents including proteins can be released when they are incubated both in the low osmolarity water and at the nonpermissive temperature(usually 37。c)．After mutagenesis by using nitrosoguanidine,a highlythermosensitive and permeable mutant named Z114 was obtained from themarine yeast Cryptococcus aureus G7a．Ofthe total protein．65．3%was releasedfrom the mutant cells suspended in distilled water after they were treated at 37。Covernight．However．only 12．3%of the total protein was released from the mutantcells suspended in 1．0 M sorbitol solution after they were treated at 37。Covernight．We found that intracellular density of the mutant treated at 37。C wasgreatly decreased,and cell volume of the mutant treated at 37。C was increaseddue to the increased protein release．However,no significant changes in theintracellular density and cell volume of the mutant were observed when its cellssuspended in 1．0 M sorbitol solution were treated at 37。C．It was found that no bigchanges in cell growth,protein content,vitamin C content,nucleic acid content,fatty acids,and amino acid compositions ofboth the mutant and its wild type weredetected．Therefore,the highly thermosensitive and permeable mutant still can bea good candidate as single-cell protein．This means that the method used in thisstudy is a simple and efficient way to release protein from the highlythermosensitive and permeable yeast mutant cells with high protein content．The intracellular protein in the highly thermosensitive and permeable mutantcan be easily released when they are incubated both in the low-osmolarity waterand at the non-permissive temperature(usually 37 O．After the mutant wasgrown in the yacon extract for 45 h,the crude protein content in the highlythermosensitive and permeable mutant Z114 was 59．1%and over 61%ofthe totalprotein could be released from the cells treated at 37 C．The mutant cells grown in the yacon extract still contained high level of essential amino acids and othernutrients．This means that the yacon extract could be used as the medium forgrowth of the highly thermosensitive and permeable mutant which contained highcontent of crude protein．...