diff --git a/pkg/obiiter/workers.go b/pkg/obiiter/workers.go
index 257cdae..1ff72d9 100644
--- a/pkg/obiiter/workers.go
+++ b/pkg/obiiter/workers.go
@@ -1,6 +1,8 @@
 package obiiter
 
 import (
+	"runtime"
+
 	log "github.com/sirupsen/logrus"
 
 	"git.metabarcoding.org/obitools/obitools4/obitools4/pkg/obioptions"
@@ -24,42 +26,8 @@ func (iterator IBioSequence) MakeIWorker(worker obiseq.SeqWorker,
 		nworkers = sizes[0]
 	}
 
-	newIter := MakeIBioSequence()
-
-	newIter.Add(nworkers)
-
-	go func() {
-		newIter.WaitAndClose()
-		log.Debugln("End of the batch workers")
-
-	}()
-
 	sw := obiseq.SeqToSliceWorker(worker, breakOnError)
-
-	f := func(iterator IBioSequence) {
-		var err error
-		for iterator.Next() {
-			batch := iterator.Get()
-			batch.slice, err = sw(batch.slice)
-			if err != nil && breakOnError {
-				log.Fatalf("Error on sequence processing : %v", err)
-			}
-			newIter.Push(batch)
-		}
-		newIter.Done()
-	}
-
-	log.Debugln("Start of the batch workers")
-	for i := 0; i < nworkers-1; i++ {
-		go f(iterator.Split())
-	}
-	go f(iterator)
-
-	if iterator.IsPaired() {
-		newIter.MarkAsPaired()
-	}
-
-	return newIter
+	return iterator.MakeISliceWorker(sw, breakOnError, nworkers)
 }
 
 // MakeIConditionalWorker applies a given worker function to each sequence in the iterator that satisfies the given predicate.
@@ -80,42 +48,10 @@ func (iterator IBioSequence) MakeIConditionalWorker(predicate obiseq.SequencePre
 		nworkers = sizes[0]
 	}
 
-	newIter := MakeIBioSequence()
-
-	newIter.Add(nworkers)
-
-	go func() {
-		newIter.WaitAndClose()
-		log.Debugln("End of the batch workers")
-
-	}()
-
 	sw := obiseq.SeqToSliceConditionalWorker(predicate, worker, breakOnError)
 
-	f := func(iterator IBioSequence) {
-		var err error
-		for iterator.Next() {
-			batch := iterator.Get()
-			batch.slice, err = sw(batch.slice)
-			if err != nil && breakOnError {
-				log.Fatalf("Error on sequence processing : %v", err)
-			}
-			newIter.Push(batch)
-		}
-		newIter.Done()
-	}
+	return iterator.MakeISliceWorker(sw, breakOnError, nworkers)
 
-	log.Debugln("Start of the batch workers")
-	for i := 0; i < nworkers-1; i++ {
-		go f(iterator.Split())
-	}
-	go f(iterator)
-
-	if iterator.IsPaired() {
-		newIter.MarkAsPaired()
-	}
-
-	return newIter
 }
 
 // MakeISliceWorker applies a SeqSliceWorker function to each slice in the IBioSequence iterator,
@@ -137,13 +73,6 @@ func (iterator IBioSequence) MakeISliceWorker(worker obiseq.SeqSliceWorker, brea
 
 	newIter := MakeIBioSequence()
 
-	newIter.Add(nworkers)
-
-	go func() {
-		newIter.WaitAndClose()
-		log.Println("End of the batch slice workers")
-	}()
-
 	f := func(iterator IBioSequence) {
 		var err error
 		for iterator.Next() {
@@ -153,16 +82,25 @@ func (iterator IBioSequence) MakeISliceWorker(worker obiseq.SeqSliceWorker, brea
 				log.Fatalf("Error on sequence processing : %v", err)
 			}
 			newIter.Push(batch)
+			runtime.GC()
 		}
 		newIter.Done()
 	}
 
-	log.Printf("Start of the batch slice workers on %d workers\n", nworkers)
-	for i := 0; i < nworkers-1; i++ {
+	log.Debugln("Start of the batch workers")
+	for i := 1; i < nworkers; i++ {
+		newIter.Add(1)
 		go f(iterator.Split())
 	}
+	newIter.Add(1)
 	go f(iterator)
 
+	go func() {
+		newIter.WaitAndClose()
+		log.Debugln("End of the batch workers")
+
+	}()
+
 	if iterator.IsPaired() {
 		newIter.MarkAsPaired()
 	}
diff --git a/pkg/obitools/obiconvert/sequence_writer.go b/pkg/obitools/obiconvert/sequence_writer.go
index 308a6c9..52e2e50 100644
--- a/pkg/obitools/obiconvert/sequence_writer.go
+++ b/pkg/obitools/obiconvert/sequence_writer.go
@@ -1,6 +1,8 @@
 package obiconvert
 
 import (
+	"io/fs"
+	"os"
 	"path/filepath"
 	"strings"
 
@@ -93,6 +95,15 @@ func CLIWriteBioSequences(iterator obiiter.IBioSequence,
 			newIter, err = obiformats.WriteSequencesToFile(iterator, fn, opts...)
 		}
 	} else {
+		log.Info("Output is done on stdout")
+		var s fs.FileInfo
+		s, err = os.Stdout.Stat()
+		if err != nil {
+			return obiiter.NilIBioSequence, err
+		}
+
+		log.Infof("Data is writen to %s", s.Name())
+
 		opts = append(opts, obiformats.OptionsSkipEmptySequence(CLISkipEmpty()))
 		switch CLIOutputFormat() {
 		case "fastq":
diff --git a/pkg/obitools/obipcr/pcr.go b/pkg/obitools/obipcr/pcr.go
index cf5312f..3b36b9d 100644
--- a/pkg/obitools/obipcr/pcr.go
+++ b/pkg/obitools/obipcr/pcr.go
@@ -60,5 +60,5 @@ func CLIPCR(iterator obiiter.IBioSequence) (obiiter.IBioSequence, error) {
 		iterator = iterator.Pipe(frags)
 	}
 
-	return iterator.MakeISliceWorker(worker, false, obioptions.CLIParallelWorkers(), 0), nil
+	return iterator.MakeISliceWorker(worker, false, obioptions.CLIParallelWorkers()), nil
 }
diff --git a/pkg/obitools/obitag/obitag.go b/pkg/obitools/obitag/obitag.go
index 9fdb7c3..48318d3 100644
--- a/pkg/obitools/obitag/obitag.go
+++ b/pkg/obitools/obitag/obitag.go
@@ -293,7 +293,9 @@ func CLIAssignTaxonomy(iterator obiiter.IBioSequence,
 		if err == nil {
 			j++
 		} else {
-			log.Warnf("Taxid %d is not described in the taxonomy. Sequence %s is discared from the reference database", seq.Taxid(), seq.Id())
+			log.Warnf("Taxid %d is not described in the taxonomy."+
+				      " Sequence %s is discared from the reference database", 
+					  seq.Taxid(), seq.Id())
 		}
 	}