All tRNAHis possess an essential extra G–1 guanosine residue at their 5′ end. In eukaryotes after standard processing by RNase P, G–1 is added by a tRNAHis guanylyl transferase. In prokaryotes, G–1 is genome-encoded and retained during maturation. In plant mitochondria, although trnH genes possess a G–1 we find here that both maturation pathways can be used. Indeed, tRNAHis with or without a G–1 are found in a plant mitochondrial tRNA fraction. Furthermore, a recombinant Arabidopsis mitochondrial RNase P can cleave tRNAHis precursors at both positions G+1 and G–1. The G–1 is essential for recognition by plant mitochondrial histidyl-tRNA synthetase. Whether, as shown in prokaryotes and eukaryotes, the presence of uncharged tRNAHis without G–1 has a function or not in plant mitochondrial gene regulation is an open question. We find that when a mutated version of a plant mitochondrial trnH gene containing no encoded extra G is introduced and expressed into isolated potato mitochondria, mature tRNAHis with a G–1 are recovered. This shows that a previously unreported tRNAHis guanylyltransferase activity is present in plant mitochondria.

A metagenomic fosmid expression library established from environmental DNA (eDNA) from the shallow hot vent sediment sample collected from the Levante Bay, Vulcano Island (Aeolian archipelago) was established in Escherichia coli. Using activity-based screening assays, we have assessed 9600 fosmid clones corresponding to approximately 350 Mbp of the cloned eDNA, for the lipases/esterases/lactamases, haloalkane and haloacid dehalogenases, and glycoside hydrolases. Thirty-four positive fosmid clones were selected from the total of 120 positive hits and sequenced to yield ca. 1360 kbp of high-quality assemblies. Fosmid inserts were attributed to the members of ten bacterial phyla, including Proteobacteria, Bacteroidetes, Acidobateria, Firmicutes, Verrucomicrobia, Chloroflexi, Spirochaetes, Thermotogae, Armatimonadetes, and Planctomycetes. Of ca. 200 proteins with high biotechnological potential identified therein, we have characterized in detail three distinct α/β-hydrolases (LIPESV12_9, LIPESV12_24, LIPESV12_26) and one new α-arabinopyranosidase (GLV12_5). All LIPESV12 enzymes revealed distinct substrate specificities tested against 43 structurally diverse esters and 4 p-nitrophenol carboxyl esters. Of 16 different glycosides tested, the GLV12_5 hydrolysed only p-nitrophenol-α-(l)-arabinopyranose with a high specific activity of about 2.7 kU/mg protein. Most of the α/β-hydrolases were thermophilic and revealed a high tolerance to, and high activities in the presence of, numerous heavy metal ions. Among them, the LIPESV12_24 was the best temperature-adapted, retaining its activity after 40 min of incubation at 90 °C. Furthermore, enzymes were active in organic solvents (e.g., >30 % methanol). Both LIPESV12_24 and LIPESV12_26 had the GXSXG pentapeptides and the catalytic triads Ser-Asp-His typical to the representatives of carboxylesterases of EC 3.1.1.1.Electronic supplementary materialThe online version of this article (doi:10.1007/s00253-015-6873-x) contains supplementary material, which is available to authorized users.